Guidance on the application of the CLP Criteria : guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures. Part 2, Physical hazards.
Date: 2025-01-08
Institutions: European Chemicals Agency
Subjects: chemical industry, chemical product, chemicals legislation, classification, dangerous substance, environmental protection, labelling, packaging, public health, risk management, user guide

Guidance on the Application of the CLP Criteria, Part 2 

Version X.x – XXX 20XX 

1 

G U I D A N C E  

Guidance on the Application of the CLP 
Criteria 

Part 2: Physical Hazards  

Guidance to Regulation (EC) No 1272/2008 on classification, labelling 
and packaging (CLP) of substances and mixtures 

Version 4.0 
Nov 2024 

 
 
 
 
 
 
 
 
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Guidance on the Application of the CLP Criteria, Part 2 

Version 4.0 – Nov 2024 

LEGAL NOTICE 

This document aims to assist users in complying with their obligations under the CLP Regulation. 
However,  users  are  reminded  that  the  text  of  the  CLP  Regulation  is  the  only  authentic  legal 
reference and that the information in this document does not constitute legal advice. Usage of 
the  information  remains  under  the  sole  responsibility  of  the  user.  The  European  Chemicals 
Agency does not accept any liability with regard to the use that may be made of the information 
contained in this document. 

Guidance on the Application of CLP Criteria 

Reference: 
Cat.Number:  
ISBN:  
DOI:   
Publ.date:  
Language:    

ECHA-24-G-07-EN 
ED-01-24-013-EN-N 
978-92-9468-409-7 
10.2823/9211338 
Nov 2024 
EN 

© European Chemicals Agency, 2024 

If you have questions or comments in relation to this document, please send them (quote the 
reference and issue date) using the information request form. The information request form can 
be accessed via the Contact ECHA page at: https://echa.europa.eu/contact 

European Chemicals Agency 

Mailing address: P.O. Box 400, FI-00121 Helsinki, Finland 
Visiting address: Telakkakatu 6, Helsinki 00150, Finland 

 
 
 
 
 
 
 
 
 
 
Guidance on the Application of the CLP Criteria, Part 2 

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3 

DOCUMENT HISTORY 

Version 

Comment 

Version 1.0  First edition 

n.a. 

Please note that change between the version published in August 
2009 and that of April 2011 are not recorded in this document 
history.  

Date 

August 2009 

April 2011 

Version 2.0  Revision of the CLP Guidance addressing content in relation to 
the  Part  2:  Physical  hazards  following  the  2nd  and  the  4th 
Adaptation  to  Technical  Progress  to  the  CLP  Regulation 
(Commission  Regulation  (EU)  No  286/2011  of  10  March  2011 
and Commission Regulation (EU) No 487/2013 of 8 May 2013). 

November 
2013 

The revision includes: 

•  Numbering of chapters within CLP Guidance, Part 2 was 
synchronised  with  corresponding  chapter  numbering  of 
CLP, Annex I. 

•  Changes in the legal text due the 2nd and 4th ATPs. 

•  Changes  in  the  legal  text  due  to  the  4th  ATP  were 
highlighted in orange within all relevant green boxes. All 
changes are preceded by a note highlighting the changes. 
(To note: a corrigendum will change the colour of relative 
legal text boxes from orange to green when the 4th ATP 
applies). 

In addition, the revisions to Part 2: Physical hazards include the 
following: 

•  Chapters  ‘Pyrophoric  liquids  and  solids’  and  ‘Oxidising 
liquids  and  solids’  were  divided  into  four  chapters: 
‘Pyrophoric liquids’, ‘Pyrophoric solids’, ‘Oxidising liquids’ 
and ‘Oxidising solids’ respectively. 

•  Based  on  the  4th  ATP  the  CLP  Guidance  Chapter  2.2 
Flammable gases was extended to take into account the 
scope of CLP, Annex I, section 2.2 to include chemically 
unstable gases.  

•  Further, the 4th ATP amended the criteria in CLP Annex I, 
Section 2.3 Flammable aerosols and renamed it into 2.3 
Aerosols.  Hence,  the  CLP  Guidance  was  amended 
accordingly.  

•  All  chapters  were  rechecked  and  redundant  and/or 
outdated  information  were  deleted,  reorganised  and/or 
revised.  For  example,  ‘Introduction’  chapters  were 
significantly  shortened,  however  several  “examples” 
sections  (i.e.  ‘Example  for  classification…’)  were  further 
elaborated. 

•  Where  missing,  a  new  sub-chapter  ‘Relation  to  other 

physical hazards’ was added. 

 
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•  Sub-chapter  2.0.4  ‘Physical  state’  was  extended  with 
additional information about substance/mixture form and 
some examples.  

• 

• 

In  sub-chapter  2.1.5.2  ‘Additional  labelling  provisions’ 
within  chapter  2.1  ‘Explosives’  further  guidance  about 
hazard communication was provided. 

In  sub-chapter  2.5.6.1  a  new  recommendation  for  shot 
hazard codes to identify the classification of gasses under 
pressure was added.  

•  Footnotes  with  references  to  endorsed  or  on-going 
revisions  of  the  GHS  which  have  not  yet  been 
implemented  into  the  CLP  via  a  respective  ATP  were 
included  in  relevant  sub-chapters  of  this  guidance  for 
information only. 

Version 2.1  Corrigendum to take account of the end of the transition period 
of the 4th ATP (as foreseen in version 4.0 above): 

June 2015 

•  change the colour of relative legal text boxes from orange 

• 

to green;  
in  Part  2,  to  delete  section  2.2.1  Flammable  gases  and 
section  2.3.1  Flammable  Aerosols  (outdated  text)  and 
renumber  sections  2.2.2  Flammable  gases  (including 
chemically  unstable  gases)  and  2.3.2  Aerosols 
accordingly; 

In addition, minor editorial errors were corrected and minor 
reformatting was made. 

Version 3.0  Partial  revision  of  the  Guidance  to  update  the  content  mainly 
following  the  8th  Adaptation  to  Technical  Progress  to  the  CLP 
Regulation  (Commission  Regulation  (EU)  No  286/2011). 
Revision of few specific additional topics. 

July 2017 

The update includes the following: 

(i) Throughout the document: 

•  Revision of legal references and legal text quotations. 

•  Renumbering of some sections. 

•  Deletion  of  sections  regarding  the  reclassification  of 
substances  and  mixtures  previously  classified 
in 
accordance with the DSD or DPD. 

(ii) Revision of the following sections of Part 2: 

•  2.1  (Explosives):  replacement  of  new  figure  2.1.3; 
update  of  label  elements;  addition  new  note  2  to  table 
2.1.2 on requirement for SDSs. 

•  2.3  (Aerosols):  update  of  text  on  classification  criteria; 
update of decision logic 2.3.1-a; update of section 2.3.6 
on the relation to transport classification. 

 
 
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•  2.14 (Oxidising solids): addition of criteria using test 0.3; 

update of labelling elements. 

(iii) Minor changes to the following sections in Part 2: 

•  2.8 (Self-reactive): update of label elements. 

•  2.12  (Emitting  flammable  gases):  update  of  label 

elements. 

•  2.15 

(Organic  peroxides):  update  of  decision 

logic.2.15.1; update of label elements. 

Version 4.0  Substantial update of all hazard classes (sections 2.1 – 2.16) to 

Nov 2024 

account for: 

•  CLP ATP 12 
•  Updates to test guidelines 
•  Developments in science 
•  Clarifications  on  comparability  between  EU  and  UN 

methods 

•  Removal of references to DSD 

Addition of section 2.17 on desensitised explosives. 

CLP Guidance Part 2 re-presented as separate document. 

NOTEs to the reader:  

In this document, text cited from Regulation (EC) No 1272/2008 is indicated in green boxes in 
italic font. 

  This symbol highlights text to be noted. 

 
 
 
 
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Table of Contents 

PART 2: PHYSICAL HAZARDS .............................................................. 18 

2.0. 

INTRODUCTION ................................................................................... 18 
2.0.1  General remarks about the prerequisites for classification and testing ................... 18 
2.0.2  Safety ........................................................................................................... 18 
2.0.3  General conditions for testing .......................................................................... 18 
2.0.4 
Physical state ................................................................................................. 19 
2.0.5  Quality .......................................................................................................... 20 

2.1.4.1. 
2.1.4.2. 
2.1.4.3. 
2.1.4.4. 
2.1.4.5. 

2.1.  EXPLOSIVES ....................................................................................... 21 
2.1.1. 
Introduction ................................................................................................... 21 
2.1.2.  Definitions and general considerations for classification of explosives .................... 21 
2.1.3.  Relation to other physical hazards .................................................................... 22 
2.1.4.  Classification of substances, mixtures or articles as explosives ............................. 23 
Identification of hazard information .......................................................... 23 
Screening procedures and waiving of testing .............................................. 23 
Classification criteria ............................................................................... 25 
Testing and evaluation of hazard information ............................................. 26 
Classification procedure and decision logics................................................ 26 
2.1.4.5.1.  Acceptance procedure ......................................................................... 27 
2.1.4.5.2.  Assignment procedure to a division ....................................................... 30 
2.1.5.  Hazard communication for explosives................................................................ 36 
Pictograms, signal words, hazard statements and precautionary statements .. 36 
Additional labelling provisions .................................................................. 37 
2.1.5.2.1.  Packaging dependence ........................................................................ 37 
2.1.5.2.2.  Supplemental hazard information ......................................................... 38 
Further communication requirements ........................................................ 39 
2.1.6.  Relation to transport classification .................................................................... 39 
2.1.7.  Example of classification for explosives ............................................................. 39 
Example of substances and mixtures fulfilling the classification criteria .......... 39 
Example of substances and mixtures not fulfilling the classification criteria .... 41 

2.1.7.1. 
2.1.7.2. 

2.1.5.1. 
2.1.5.2. 

2.1.5.3. 

2.2.  FLAMMABLE GASES .............................................................................. 45 
2.2.1. 
Introduction ................................................................................................... 45 
2.2.2.  Definitions and general considerations for classification of flammable gases ........... 45 
2.2.3.  Relation to other physical hazards .................................................................... 45 
2.2.4.  Classification of substances, mixtures or articles as flammable gases .................... 46 
Identification of hazard information .......................................................... 46 
2.2.4.1. 
Screening procedures and waiving of testing .............................................. 46 
2.2.4.2. 
Classification criteria ............................................................................... 47 
2.2.4.3. 
2.2.4.4. 
Testing and evaluation of hazard information ............................................. 48 
2.2.4.5.  Decision logics ....................................................................................... 50 
2.2.5.  Hazard communication for flammable gases ...................................................... 54 
Pictograms, signal words, hazard statements and precautionary statements .. 54 
2.2.6.  Relation to transport classification .................................................................... 56 
2.2.7.  Example of classification for flammable gases .................................................... 56 
2.2.8.  References .................................................................................................... 58 

2.2.5.1. 

2.3.  AEROSOLS .......................................................................................... 58 
Introduction ................................................................................................... 58 

2.3.1. 

 
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2.3.2.  Definitions and general considerations for classification of aerosols ....................... 58 
2.3.3.  Relation to other physical hazards .................................................................... 58 
2.3.4.  Classification of aerosols ................................................................................. 59 
Classification criteria ............................................................................... 59 
2.3.4.1. 
2.3.4.2. 
Testing and evaluation of hazard information ............................................. 60 
2.3.4.3.  Decision logics ....................................................................................... 61 
2.3.4.3.1.  Decision logics for aerosols .................................................................. 62 
2.3.4.3.2.  Decision logics for spray aerosols.......................................................... 63 
2.3.4.3.3.  Decision logics for foam aerosols .......................................................... 64 
2.3.5.  Hazard communication for aerosols .................................................................. 64 
Pictograms, signal words, hazard statements and precautionary statements .. 64 
Additional labelling provisions .................................................................. 65 
2.3.6.  Relation to transport classification .................................................................... 65 
2.3.7.  Example of classification for aerosols ................................................................ 65 
Example of substances and mixtures fulfilling the classification criteria .......... 65 
Examples of aerosols not fulfilling the classification criteria .......................... 66 

2.3.7.1. 
2.3.7.2. 

2.3.5.1. 
2.3.5.2. 

2.4.  OXIDISING GASES ............................................................................... 66 
2.4.1. 
Introduction ................................................................................................... 66 
2.4.2.  Definitions and general considerations for the classification of oxidising gases ........ 66 
2.4.3.  Relation to other physical hazards .................................................................... 67 
2.4.4.  Classification of substances and mixtures as oxidising gases ................................ 67 
2.4.4.1. 
Identification of hazard information .......................................................... 67 
2.4.4.2. 
Screening procedures and waiving of testing .............................................. 67 
2.4.4.3. 
Classification criteria ............................................................................... 67 
Testing and evaluation of hazard information ............................................. 67 
2.4.4.4. 
2.4.4.5.  Decision logic ......................................................................................... 68 
2.4.5.  Hazard communication for oxidising gases ......................................................... 68 
Pictograms, signal words, hazard statements and precautionary statements .. 68 
2.4.6.  Relation to transport classification .................................................................... 69 
2.4.7.  Example of classification for oxidising gases....................................................... 69 
Example of substances and mixtures not fulfilling the classification criteria .... 69 

2.4.5.1. 

2.4.7.1. 

2.5.  GASES UNDER PRESSURE ..................................................................... 70 
2.5.1. 
Introduction ................................................................................................... 70 
2.5.2.  Definitions and general considerations for classification of gases under pressure .... 70 
2.5.2.1.  Definition of ‘gas’ .................................................................................... 70 
2.5.2.2.  Definition of gases under pressure ............................................................ 71 
2.5.3.  Relation to other physical hazards .................................................................... 71 
2.5.4.  Classification of substances and mixtures as gases under pressure ....................... 71 
Identification of hazard information .......................................................... 71 
2.5.4.1. 
Classification criteria ............................................................................... 71 
2.5.4.2. 
2.5.4.3. 
Testing and evaluation of hazard information ............................................. 72 
2.5.4.4.  Decision logic ......................................................................................... 72 
2.5.5.  Hazard communication for gases under pressure ................................................ 74 
Pictograms, signal words, hazard statements and precautionary statements .. 74 
2.5.6.  Relation to transport classification .................................................................... 74 
2.5.7.  Example of classification for gases under pressure .............................................. 75 
Example of substances and mixtures fulfilling the classification criteria .......... 75 
2.5.7.1.1.  Example mixture: 9 % (O2) + 16 % (N2O) + 75 % (N2) .......................... 75 

2.5.5.1. 

2.5.7.1. 

2.6.  FLAMMABLE LIQUIDS ............................................................................ 76 

 
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2.6.4.1. 
2.6.4.2. 

2.6.4.3. 
2.6.4.4. 

2.6.1. 
Introduction ................................................................................................... 76 
2.6.2.  Definitions and general considerations for classification of flammable liquids .......... 76 
2.6.3.  Relation to other physical hazards .................................................................... 76 
2.6.4.  Classification of substances and mixtures as flammable liquids ............................ 76 
Identification of hazard information .......................................................... 76 
Screening procedures and waiving of testing .............................................. 76 
2.6.4.2.1.  Boiling point ....................................................................................... 76 
2.6.4.2.2.  Flash point ......................................................................................... 76 
Classification criteria ............................................................................... 77 
Testing and evaluation of hazard information ............................................. 77 
2.6.4.4.1.  Testing .............................................................................................. 77 
2.6.4.4.2.  Evaluation of hazard information .......................................................... 78 
2.6.4.5.  Decision logic ......................................................................................... 78 
2.6.5.  Hazard communication for flammable liquids ..................................................... 80 
Pictograms, signal words, hazard statements and precautionary statements .. 80 
Additional labelling provisions for flammable liquids .................................... 80 
2.6.6.  Relation to transport classification .................................................................... 81 
2.6.7.  Example of classification for flammable liquids ................................................... 81 
Example of substances and mixtures fulfilling the classification criteria .......... 81 
2.6.7.1.1.  Example 1 ......................................................................................... 81 
2.6.7.1.2.  Example 2 ......................................................................................... 82 
Example of substances and mixtures not fulfilling the classification criteria .... 82 
2.6.7.2.1.  Example 3 ......................................................................................... 82 
2.6.8.  References .................................................................................................... 83 

2.6.5.1. 
2.6.5.2. 

2.6.7.2. 

2.6.7.1. 

2.7.  FLAMMABLE SOLIDS ............................................................................. 83 
2.7.1. 
Introduction ................................................................................................... 83 
2.7.2.  Definitions and general considerations for classification of flammable solids ........... 83 
2.7.3.  Relation to other physical hazards .................................................................... 83 
2.7.4.  Classification of substances and mixtures as flammable solids .............................. 84 
2.7.4.1. 
Identification of hazard information .......................................................... 84 
2.7.4.2. 
Screening procedures and waiving of testing .............................................. 84 
2.7.4.3. 
Classification criteria ............................................................................... 84 
Testing and evaluation of hazard information ............................................. 85 
2.7.4.4. 
2.7.4.5.  Decision logic ......................................................................................... 85 
2.7.5.  Hazard communication for flammable solids ...................................................... 87 
Pictograms, signal words, hazard statements and precautionary statements .. 87 
2.7.6.  Relation to transport classification .................................................................... 87 
2.7.7.  Example of classification for flammable solids .................................................... 88 
Example of substances and mixtures fulfilling the classification criteria .......... 88 
Example of substances and mixtures not fulfilling the classification criteria .... 88 
2.7.8.  References .................................................................................................... 88 

2.7.7.1. 
2.7.7.2. 

2.7.5.1. 

2.8.  SELF-REACTIVE SUBSTANCES AND MIXTURES .......................................... 88 
Introduction ................................................................................................... 88 

2.8.1. 
2.8.2.  Definitions and general considerations for classification of self-reactive substances 

and mixtures ................................................................................................. 89 
2.8.3.  Relation to other physical hazards .................................................................... 89 
2.8.4.  Classification of substances and mixtures as self-reactive substances and mixtures 89 
Identification of hazard information .......................................................... 89 
Screening procedures and waiving of testing .............................................. 90 
Classification criteria ............................................................................... 90 

2.8.4.1. 
2.8.4.2. 
2.8.4.3. 

 
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2.8.4.4. 

Testing and evaluation of hazard information ............................................. 92 
2.8.4.4.1.  Thermal stability and temperature control ............................................. 92 
2.8.4.4.2.  Additional consideration and testing ...................................................... 93 
2.8.4.4.3.  Additional classification considerations .................................................. 94 
2.8.4.5.  Decision logic ......................................................................................... 94 
2.8.5.  Hazard communication for self-reactive substances and mixtures ......................... 97 
Pictograms, signal words, hazard statements and precautionary statements .. 97 
2.8.6.  Relation to transport classification .................................................................... 98 
2.8.7.  Example of classification for self-reactive substances and mixtures ....................... 98 
Example of substances and mixtures fulfilling the classification criteria .......... 98 

2.8.7.1. 

2.8.5.1. 

2.9.  PYROPHORIC LIQUIDS ......................................................................... 102 
2.9.1. 
Introduction ................................................................................................. 102 
2.9.2.  Definitions and general considerations for classification of pyrophoric liquids ....... 102 
2.9.3.  Relation to other physical hazards .................................................................. 102 
2.9.4.  Classification of substances and mixtures as pyrophoric liquids .......................... 102 
Identification of hazard information ........................................................ 102 
2.9.4.1. 
Screening procedures and waiving of testing ............................................ 103 
2.9.4.2. 
Classification criteria ............................................................................. 103 
2.9.4.3. 
2.9.4.4. 
Testing and evaluation of hazard information ........................................... 103 
2.9.4.5.  Decision logic ....................................................................................... 104 
2.9.5.  Hazard communication for pyrophoric liquids ................................................... 105 
Pictograms, signal words, hazard statements and precautionary statements 105 
2.9.6.  Relation to transport classification .................................................................. 105 
2.9.7.  Examples of classification for pyrophoric liquids ................................................ 106 
Examples of substances and mixtures fulfilling the classification criteria ...... 106 
2.9.7.1.1.  Example 1 ....................................................................................... 106 
2.9.7.1.2.  Example 2 ....................................................................................... 106 
Example of substances and mixtures not fulfilling the classification criteria .. 106 
2.9.7.2.1.  Example 3 ....................................................................................... 106 
2.9.8.  References .................................................................................................. 107 

2.9.7.1. 

2.9.5.1. 

2.9.7.2. 

2.10.  PYROPHORIC SOLIDS .......................................................................... 107 
2.10.1.  Introduction ................................................................................................. 107 
2.10.2.  Definitions and general considerations for classification of pyrophoric solids ......... 107 
2.10.3.  Relation to other physical hazards .................................................................. 107 
2.10.4.  Classification of substances and mixtures as pyrophoric solids ........................... 108 
2.10.4.1.  Identification of hazard information ........................................................ 108 
2.10.4.2.  Screening procedures and waiving of testing ............................................ 108 
2.10.4.3.  Classification criteria ............................................................................. 108 
2.10.4.4.  Testing and evaluation of hazard information ........................................... 109 
2.10.4.5.  Decision logic ....................................................................................... 109 
2.10.5.  Hazard communication for pyrophoric solids .................................................... 110 
2.10.5.1.  Pictograms, signal words, hazard statements and precautionary statements 110 
2.10.6.  Relation to transport classification .................................................................. 111 
2.10.7.  Examples of classification for pyrophoric solids ................................................. 111 
2.10.7.1.  Examples of substances and mixtures fulfilling the classification criteria ...... 111 
2.10.7.1.1. Example 1 ....................................................................................... 111 
2.10.7.1.2. Example 2 ....................................................................................... 111 
2.10.7.2.  Example of substances and mixtures not fulfilling the classification criteria .. 111 
2.10.7.2.1. Example 3 ....................................................................................... 111 

 
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2.10.7.2.2. Example 4 ....................................................................................... 112 
2.10.8.  References .................................................................................................. 112 

2.11.  SELF-HEATING SUBSTANCES AND MIXTURES .......................................... 112 
2.11.1.  Introduction ................................................................................................. 112 
2.11.2.  Definitions and general considerations for classification of self-heating substances 

and mixtures ............................................................................................... 112 
2.11.3.  Relation to other physical hazards .................................................................. 113 
2.11.4.  Classification of substances and mixtures as self-heating................................... 113 
2.11.4.1.  Identification of hazard information ........................................................ 113 
2.11.4.2.  Screening procedures and waiving of testing ............................................ 113 
2.11.4.3.  Classification criteria ............................................................................. 114 
2.11.4.4.  Testing and evaluation of hazard information ........................................... 115 
2.11.4.4.1. General remarks ............................................................................... 115 
2.11.4.4.2. Sample preparation .......................................................................... 115 
2.11.4.4.3. Test conduction, criteria and evaluation ............................................... 115 
2.11.4.5.  Decision logic ....................................................................................... 116 
2.11.4.6.  Exemption ........................................................................................... 117 
2.11.5.  Hazard communication for self-heating substances or mixtures .......................... 119 
2.11.5.1.  Pictograms, signal words, hazard statements and precautionary statements 119 
2.11.6.  Relation to transport classification .................................................................. 120 
2.11.7.  Examples of classification for self-heating substances or mixtures ...................... 120 
2.11.7.1.  Example of substances and mixtures fulfilling the classification criteria ........ 120 
2.11.7.2.  Example of substances and mixtures not fulfilling the classification criteria .. 122 
2.11.8.  References .................................................................................................. 122 

2.12.  SUBSTANCES  OR  MIXTURES  WHICH,  IN  CONTACT  WITH  WATER,  EMIT 

FLAMMABLE GASES ............................................................................. 123 
2.12.1.  Introduction ................................................................................................. 123 
2.12.2.  Definitions and general considerations for classification of substances or mixtures 

which, in contact with water, emits flammable gases ........................................ 123 
2.12.3.  Relation to other physical hazards .................................................................. 123 
2.12.4.  Classification  of  substances  and  mixtures  which,  in  contact  with  water,  emits 

flammable gases .......................................................................................... 124 
2.12.4.1.  Identification of hazard information ........................................................ 124 
2.12.4.2.  Screening procedures and waiving of testing ............................................ 125 
2.12.4.3.  Classification criteria ............................................................................. 125 
2.12.4.4.  Testing and evaluation of hazard information ........................................... 126 
2.12.4.4.1. Testing procedure ............................................................................. 126 
2.12.4.4.2. Evaluation of hazard information ........................................................ 127 
2.12.4.5.  Decision logic ....................................................................................... 127 

2.12.5.  Hazard  communication  for  substances  or  mixtures  which,  in  contact  with  water, 

emits flammable gases .................................................................................. 129 
2.12.5.1.  Pictograms, signal words, hazard statements and precautionary statements 129 
2.12.5.2.  Additional labelling provisions ................................................................ 129 
2.12.6.  Relation to transport classification .................................................................. 130 
2.12.7.  Example of classification for substances or mixtures which, in contact with water, 

emits flammable gases .................................................................................. 130 
2.12.7.1.  Example of substances and mixtures fulfilling the classification criteria ........ 130 
2.12.7.1.1. Example 1 ....................................................................................... 130 
2.12.7.2.  Example of substances and mixtures not fulfilling the classification criteria .. 131 
2.12.7.2.1. Example 2 ....................................................................................... 131 

 
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2.12.8.  References .................................................................................................. 131 

2.13.  OXIDISING LIQUIDS ........................................................................... 132 
2.13.1.  Introduction ................................................................................................. 132 
2.13.2.  Definitions and general considerations for classification of oxidising liquids .......... 132 
2.13.3.  Relation to other physical hazards .................................................................. 132 
2.13.4.  Classification of substances and mixtures as oxidising liquids ............................. 133 
2.13.4.1.  Identification of hazard information ........................................................ 133 
2.13.4.2.  Screening procedures and waiving of testing ............................................ 133 
2.13.4.3.  Classification criteria ............................................................................. 134 
2.13.4.4.  Testing and evaluation of hazard information ........................................... 135 
2.13.4.5.  Decision logic ....................................................................................... 135 
2.13.4.6.  Hazard communication for oxidising liquids .............................................. 136 
2.13.4.6.1. Pictograms, signal words, hazard statements and precautionary statements

  136 

2.13.5.  Relation to transport classification .................................................................. 137 
2.13.6.  Example of classification for oxidising liquids.................................................... 137 
2.13.6.1.  Example of substances and mixtures fulfilling the classification criteria ........ 137 
2.13.6.2.  Example of substances and mixtures not fulfilling the classification criteria .. 138 
2.13.7.  Reference .................................................................................................... 138 

2.14.  OXIDISING SOLIDS ............................................................................. 138 
2.14.1.  Introduction ................................................................................................. 138 
2.14.2.  Definitions and general considerations for classification of oxidising solids ........... 139 
2.14.3.  Relation to other physical hazards .................................................................. 139 
2.14.4.  Classification of substances and mixtures as oxidising solids .............................. 140 
2.14.4.1.  Identification of hazard information ........................................................ 140 
2.14.4.2.  Screening procedures and waiving of testing ............................................ 140 
2.14.4.3.  Classification criteria ............................................................................. 141 
2.14.4.4.  Testing and evaluation of hazard information ........................................... 142 
2.14.4.5.  Decision logic ....................................................................................... 142 
2.14.5.  Hazard communication for oxidising solids ....................................................... 144 
2.14.5.1.  Pictograms, signal words, hazard statements and precautionary statements 144 
2.14.6.  Relation to transport classification .................................................................. 144 
2.14.7.  Example of classification for oxidising solids ..................................................... 145 
2.14.7.1.  Example of substances and mixtures fulfilling the classification criteria ........ 145 
2.14.7.2.  Example of substances and mixtures not fulfilling the classification criteria .. 145 
2.14.8.  Reference .................................................................................................... 145 

2.15.  ORGANIC PEROXIDES .......................................................................... 145 
2.15.1.  Introduction ................................................................................................. 145 
2.15.2.  Definitions and general considerations for classification of organic peroxides........ 146 
2.15.3.  Relation to other physical hazards .................................................................. 146 
2.15.4.  Classification of substances and mixtures as organic peroxides .......................... 146 
2.15.4.1.  Identification of hazard information ........................................................ 146 
2.15.4.2.  Classification criteria ............................................................................. 147 
2.15.4.3.  Testing and evaluation of hazard information ........................................... 148 
2.15.4.3.1. Thermal stability tests and temperature control .................................... 148 
2.15.4.3.2. Additional considerations and testing .................................................. 149 
2.15.4.3.3. Additional classification considerations ................................................ 150 
2.15.4.4.  Decision logic ....................................................................................... 150 
2.15.5.  Hazard communication for organic peroxides ................................................... 152 

 
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2.15.5.1.  Pictograms, signal words, hazard statements and precautionary statements 152 
2.15.5.2.  Additional labelling provisions ................................................................ 153 
2.15.6.  Relation to transport classification .................................................................. 153 
2.15.7.  Example of classification for organic peroxides ................................................. 153 
2.15.7.1.  Example of substances and mixtures fulfilling the classification criteria ........ 153 
2.15.7.2.  Additional remarks ................................................................................ 156 

2.16.  CORROSIVE TO METALS ....................................................................... 156 
2.16.1.  Introduction ................................................................................................. 156 
2.16.2.  Definitions and general considerations for classification of corrosive to metals ..... 157 
2.16.3.  Relation to other physical hazards .................................................................. 157 
2.16.4.  Classification of substances and mixtures as corrosive to metals ........................ 157 
2.16.4.1.  Identification of hazard information ........................................................ 157 
2.16.4.2.  Screening procedures and waiving of testing ............................................ 158 
2.16.4.3.  Classification criteria ............................................................................. 159 
2.16.4.4.  Testing and evaluation of hazard information ........................................... 159 
2.16.4.4.1. General considerations ...................................................................... 159 
2.16.4.4.2. Additional notes on best practice for testing ......................................... 160 
2.16.4.5.  Decision logic ....................................................................................... 162 
2.16.5.  Hazard communication for corrosive to metals ................................................. 163 
2.16.5.1.  Pictograms, signal words, hazard statements and precautionary statements 163 
2.16.6.  Relation to transport classification .................................................................. 164 
2.16.7.  Example of classification for corrosive to metals ............................................... 164 
2.16.7.1.  Example of metal specimen plates after exposure to a corrosive mixture ..... 165 
2.16.8.  References .................................................................................................. 165 

2.17.  DESENSITISED EXPLOSIVES ................................................................. 166 
2.17.1.  Introduction ................................................................................................. 166 
2.17.2.  Definitions and general considerations for desensitised explosives ...................... 166 
2.17.3.  Relation to other physical hazards .................................................................. 167 
2.17.4.  Classification of substances and mixtures as desensitised explosives................... 167 
2.17.4.1.  Identification of hazard information ........................................................ 168 
2.17.4.2.  Screening procedures and waiving of testing ............................................ 168 
2.17.4.3.  Classification criteria ............................................................................. 168 
2.17.4.4.  Testing and evaluation of hazard information ........................................... 169 
2.17.4.5.  Decision logic ....................................................................................... 169 
2.17.5.  Hazard communication for desensitised explosives ........................................... 171 
2.17.5.1.  Pictograms, signal words, hazard statements and precautionary statements 171 
2.17.6.  Relation to transport classification .................................................................. 171 
2.17.7.  Examples of classification for desensitised explosives ........................................ 172 

ANNEX I: RELATION BETWEEN TRANSPORT AND CLP CLASSIFICATION REGARDING 

PHYSICAL HAZARDS ............................................................................ 173 

 
 
 
 
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Table of Tables 

Table 2.1 Criteria for aerosols (Table 2.3.1 of the GHS) ............................................ 60 
Table 2.2 Examples of hazards, depending on the property of the emitted gas, when 

substances and mixtures are in contact with water ..................................... 123 

Table  2.3  Minimum  mass  loss  of  specimens  after  different  exposure  times 
(corresponding  to  the  criterion  of  6.25  mm/year,  correspond  to  Table 
37.4.1.1 of UN-MTC) ............................................................................... 160 

Table  2.4  Minimum  intrusion  depths  after  exposure  times  (corresponding  to  the 
criterion  of  localised  corrosion  of  6.25  mm/year,  correspond  to  Table 
37.4.1.2 of UN-MTC) ............................................................................... 160 

Table 2.5 Examples of classified and non classified substances and mixtures in Class 

2.16 ..................................................................................................... 164 

Table I.1  Relation  between  transport  and  CLP  classifications  regarding  physical 

hazards ................................................................................................. 173 

Table of Figures 

Figure 2.1 Decision logic for oxidising gases (Decision logic 2.4 of GHS)............................. 68 
Figure 2.2 Decision logic for gases under pressure (Decision logic 2.5 of GHS) .................... 73 
Figure 2.3 Amended GHS decision logic for flammable liquids to include derogations 

for gas oil, diesel, light heating, sustained combustibility and for phrases 
EUH018, EUH209 and EUH209A (see 2.6.5.2 for more information on 
phrases) ................................................................................................... 79 
Figure 2.4 Decision logic for flammable solids (Decision logic 2.7 of GHS) .......................... 86 
Figure 2.5 Decision logic for self-reactive substance example: NP, technically pure ............. 101 
Figure 2.6  Decision logic for pyrophoric liquids (Decision logic 2.9 of GHS) ...................... 104 
Figure 2.7  Decision logic for pyrophoric solids (Decision logic 2.10 of GHS) ...................... 110 
Figure 2.8 Extrapolation towards large volumes .............................................................. 118 
Figure 2.9 Results of UN N.4 Test according to the UN-MTC .............................................. 120 
Figure 2.10 Results of UN N.4 Test according to the UN-MTC ............................................ 121 
Figure 2.11 Volume dependency of the critical temperature for charcoal ............................ 122 
Figure 2.12 Decision logic for substances and mixtures which, in contact with water, 

emit flammable gases (Decision logic 2.12 of GHS) ........................................ 128 
Figure 2.13 Decision logic for oxidising liquids (Decision logic 2.13 of GHS) ........................ 136 
Figure 2.14 Decision logic for oxidising solids (Decision logic 2.14 of GHS) ......................... 143 
Figure 2.15 Potential pH (also called Pourbaix) diagram for iron in water at 25 °C, 

indicating stable form of the Fe element and implicitly, corrosion domains ........ 157 

Figure 2.16 Example of testing equipment available on the market to perform UN Test 

C.1  162 

Figure 2.17 Decision logic for substances and mixtures corrosive to metals (Decision 

logic 2.16 of GHS) ..................................................................................... 163 

Figure 2.18 Example of corroded metal plates after testing according to UN Test C.1 

for a classified mixture ............................................................................... 165 

. 

 
 
 
 
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LIST OF ABBREVIATIONS 

Explanation  

Standard 
term / 
Abbreviati
on  

ADD 

Directive 75/324/EEC on aerosol dispensers1 

ADN 

ADR 

European Agreement concerning the International Carriage of Dangerous Goods 
by Inland Waterways (Accord européen relatif au transport international des 
marchandises dangereuses par voie de navigation intérieure)2 

European Agreement concerning the International Carriage of Dangerous Goods 
by Road (Accord européen relatif au transport international des marchandises 
dangereuses par route)3 

ANE 

Ammonium Nitrate Emulsion 

ANFO 

Ammonium Nitrate/Fuel Oil 

ASTM 

American Society for the Testing of Materials 

ATP 

Adaptation to Technical Progress (ATP) to the CLP Regulation 

BAM 

Bundesanstalt für Materialforschung und -prüfung (Federal Institute for Materials 
Research and Testing) 

BP 

Boiling point 

CLP 

Regulation (EC) No 1272/2008 on classification, labelling and packaging of 
substances and mixtures4 

1  Directive  (75/324/EEC)  of  the  Council  on  the  approximation  of  the  laws  of  the  Member  States  relating  to  aerosol 
dispensers  [OJ  L  147,  9.6.1975,  p.40].  Directive  as  last  amended  by  Commission  Directive  2013/10/EU  [  OJ  L  77, 
20.03.2013, p.20]. 

2  European  Agreement  concerning  the  International  Carriage  of  Dangerous  Goods  by  Inland  Waterways,  concluded  at 
Geneva on 26 May 2000, as amended. 

3 European Agreement concerning the International Carriage of Dangerous Goods by Road, concluded at Geneva on 30 
September 1957, as amended. 

4 Regulation (EC) No 1272/2008 of the European Parliament and Council of 16 December 2008 on classification, labelling 
and  packaging  of  substances  and  mixtures,  amending  and  repealing  Directives  67/548/EEC  and  1999/45/EC  and 
amending Regulation (EC) No 1907/2006 [OJ L 353, 31.12.2008, p. 1]. 

 
 
 
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CSA 

Chemical Safety Assessment 

DDT 

Deflagration to Detonation Transition 

DIN 

Deutsches Institut für Normung (German Institute for Standardisation)  

DPD 

DSD 

Directive 1999/45/EC on the classification and labelling of Dangerous 
Preparations5 

Directive 67/548/EEC on the classification and labelling of Dangerous 
Substances6 

ECHA 

European Chemicals Agency, Helsinki (https://echa.europa.eu/) 

EIGA 

European Industrial Gases Association 

EIS 

Extremely Insensitive Substance 

EN 

A European Standard 

EN ISO 

European Union International Organization for Standardisation 

EU 

European Union 

EUH 

The hazard statements carried through from DSD and DPD, which are not yet 
included in the GHS are codified as ‘EUH’ 

GHS 

Globally Harmonised System of Classification and Labelling of Chemicals7 

GLP 

Good Laboratory Practice 

5 Directive 1999/45/EC of the European Parliament and of the Council of 31 May 1999 concerning the approximation of 
the  laws,  regulations  and  administrative  provisions  of  the  Member  States  relating  to  the  classification,  packaging  and 
labelling of dangerous preparations [OJ L 200, 30.7.1999, p. 1]. 

6 Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and administrative provisions 
relating to the classification, packaging and labelling of dangerous substances [OJ 196, 16.8.1967, p. 1]. 

7 Globally Harmonised System of Classification and Labelling of Chemicals (GHS), Fifth revised edition, United Nations, 
New York and Geneva, 2013. 

 
 
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IBC 

Intermediate Bulk Container 

ICAO TI 

International Civil Aviation Organization (Technical Instructions for the Safe 
Transport of Dangerous Goods by Air) 

IEC 

International Electrotechnical Commission (http://www.iec.ch/) 

IMDG 
Code 

International Maritime Dangerous Goods Code 

IMO 

International maritime Organisation 

IR&CSA 

Guidance on Information Requirements and Chemical Safety Assessment, ECHA 
(http://guidance.echa.europa.eu/docs/guidance_document/information_require
ments_en.htm) 

ISO 

International Organisation for Standardization 

ITDG 

Directive 2008/68 on the Inland Transport of Dangerous Goods8 

LEL 

Lower Explosion Limit 

LFL 

Lower Flammability Limit 

n.a. 

Not available  

REACH 

Regulation (EC) No 1907/2006 of the European Parliament and of the Council 
concerning the Registration, Evaluation, Authorisation and Restriction of 
Chemicals9 

8 Directive 2008/68/EC of the European Parliament and of the Council of 24 September 2008 on the inland transport of 
dangerous goods, implementing the European Agreement concerning the International Carriage of Dangerous Goods by 
Road (ADR), the Regulations concerning the International Carriage of Dangerous Goods by Rail (RID) and the European 
Agreement concerning the International Carriage of Dangerous Goods by Inland Waterways (ADN) [OJ L 260, 30.9.2008, 
p. 13]. 

9  Regulation  (EC)  No 1907/2006 of  the  European  Parliament  and  of  the  Council  of  18 December 2006  concerning  the 
Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European Chemicals Agency, 
amending Directive 1999/45/EC and repealing Council Regulation (EEC) No 793/93 and Commission Regulation (EC) No 
1488/94  as  well  as  Council  Directive  76/769/EEC  and  omission  of  Directives  91/155/EEC,  93/67/EEC,  93/105/EC  and 
2000/21/EC. [OJ L 396, 30.12.2006 p.1.] [Corrigendum: OJ L 136, 29.5.2007 p.3]. 

 
 
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RID 

Règlement concernant le transport international ferroviaire de marchandises 
dangereuses (Regulations concerning the International Carriage of Dangerous 
Goods by Rail)10 

RTD 

Resistance To Detonation 

SADT 

Self-Accelerating Decomposition Temperature 

SDS 

Safety Data Sheet 

UEL 

Upper Explosion Limit 

UN 

United Nations 

UN RTDG 
Model 
Regulation
s 

UN Recommendations on the Transport of Dangerous Goods - Model 
Regulations. It covers all modal transport regulations (ADR, RID, ADN, IMDG 
and ITDG). It is regularly updated and amended every two years.  

More information and the latest revision are available at: 
http://www.unece.org/trans/danger/publi/unrec/rev13/13nature_e.html  

UN-MTC 

The UN Manual of Tests and Criteria contains criteria, test methods and 
procedures to be used for classification of dangerous goods according to the 
provisions of Parts 2 and 3 of the United Nations Recommendations on the 
Transport of Dangerous Goods, Model Regulations, as well as of chemicals 
presenting physical hazards according to the Globally Harmonized System of 
Classification and Labelling of Chemicals (GHS). More information and the latest 
revision are available at: 
http://www.unece.org/trans/danger/publi/manual/manual_e.html. 

VDI 

Verein Deutscher Ingenieure (The Association of German Engineers) 

NOTEs to the reader:  

In this document, text cited from Regulation (EC) No 1272/2008 is indicated in green 
boxes in italic font. 

  This symbol highlights text to be noted. 

10  Regulations  concerning  the  International  Carriage  of  Dangerous  Goods  by  Rail,  appearing  as  Appendix  C  to  the 
Convention concerning International Carriage by Rail (COTIF) concluded at Vilnius on 3 June 1999, as amended. 

 
 
 
 
 
 
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PART 2: PHYSICAL HAZARDS 

2.0.  INTRODUCTION 

2.0.1 

General remarks about the prerequisites for classification and testing 

The purpose of this chapter is to give some general guidance with respect to the classification of 
physical hazards, the generation of test data and their interpretation. The general principles of 
the  classification  process  are  explained  Part  1  section  1.1.3,  so  this  section  refers  to  physical 
hazard specificities. 

Test methods for physical hazards are referred to in each physical hazard class chapter of CLP. 
Most of these test methods can be found in the UN Manual of Tests and Criteria11 (UN-MTC), see 
the  website  http://www.unece.org/trans/danger/publi/manual/manual_e.html.  A  few  of  these 
test  methods  are  contained  in  standards  which  are  also  referred  to  in  CLP  (see  particularly 
flammable  gases,  oxidising  gases  and  flammable  liquids).  When  test  results,  based  on  other 
methods or standards (which are not referred to in CLP) are available, then these data may still 
be used, provided they are adequate for the purpose of hazard determination. Expert judgement 
is necessary to conclude whether there is sufficient documentation to assess the suitability of the 
test  method  used,  and  whether  the  test  was  carried  out  using  an  acceptable  level  of  quality 
assurance and thus on the adequacy of such data for the purposes of classification according to 
CLP. 

Please note that in practice the physical hazards of a substance or mixture may differ from those 
shown  by  tests,  e.g.,  in  case  of  certain  ammonium-nitrate-based  compounds  (explosive  / 
oxidising  properties)  and  certain  halogenated  hydrocarbons  (flammable  properties).  Such 
experience must be taken into account for the purpose of classification (CLP, Article 12(a)). 

The information available or generated must be checked to determine if it is directly comparable 
to  the  respective  hazard  criteria  and  if  it  is,  then  it  can  be  used  to  derive  the  classification 
immediately. Where the criteria cannot be directly applied to the available data, expert judgement 
should  be  used  for  the  evaluation  of  the  available  information  in  a  weight  of  evidence 
determination (CLP, Article 9(3) and CLP Annex I, section 1.1.1.). 

2.0.2 

Safety 

Special  care  is  required  when  new  or  unknown  substances  or  mixtures  are  tested.  If  possible, 
preliminary  tests  should  be  carried  out  before  larger  quantities  are  handled.  The  'screening 
procedures’,  described  in  Appendix  6  of  UN-MTC,  allows  gathering  valuable  information  about 
physico-chemical properties based on small-scale tests. Further aspects of safety are given in the 
general  introduction,  section  1.4  of  the  UN-MTC  revision  812  or  within  the  individual  test 
procedures. 

2.0.3 

General conditions for testing 

Samples offered for testing must in all aspects be representative of the substance or mixture to 
be  classified.  Therefore,  it  is  helpful  to  characterise  or  specify  the  sample  for  the  purposes  of 
documentation (i.e. batch number, production code, impurities etc.). Further characterisation (i.e. 

11 It  should  be  noted  that  before  GHS  revision  7,  the  official  name  of  this  manual  was  “UN  Recommendations  on  the 
Transport of Dangerous Goods  – Manual of Tests and Criteria”, which is abbreviated “UN RTDG  - Manual of Tests and 
Criteria” in the CLP Regulation. However, as of GHS revision 7 the official name was changed to “Manual of Tests and 
Criteria”.  For  this  reason,  references  to  this  manual  are  denoted  as  “Manual  of  Test  and  Criteria”  or  “UN-MTC”  when 
occurring in plain text in this guidance, while they are denoted “UN RTDG - Manual of Tests and Criteria” when occurring 
in direct quotes from CLP. 

12 Unless otherwise specified, references to sections, tables, figures, etc. are consistent with UN-MTC revision 8 (2023). 

 
 
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analysis) is highly recommended in cases where the presence of diluents, activators, stabilisers 
or moisture may influence the outcome of the test. 

The tests must be performed on the substance or mixture in the appropriate physical form where 
changes  in  that  form  may  influence  the  outcome  of  the  test  (CLP,  Articles  5  and  6),  see  CLP 
Guidance  Part  1,  Section  1.2.3.1.  In  some  cases,  test  methods  as  stipulated  in  the  relevant 
physical hazards sections provide further information on the physical forms that should be tested 
and whether manipulation of the substance is required (e.g. grinding to decrease particle size). 

If additional parameters, such as physical condition, particle size and shape, specific surface area, 
density, or crystal structure influence the test result, these parameters should be mentioned in 
the test report. 

2.0.4  Physical state 

The  physical  state  determines  which  hazard  classes  should  be  considered  for  testing.  As  CLP 
states13, hazard classification is based on intrinsic properties of the substance or mixture which 
are determined not only by its physical state but also its form. 

The definitions for gases, liquids and solids are given in Annex I, Part 1 of CLP: 

Annex I: Part 1, 1.0. 

Definitions 

Gas means a substance which:  

(i) at 50 °C has a vapour pressure greater than 300 kPa (absolute); or  

(ii) is completely gaseous at 20 °C at a standard pressure of 101.3 kPa; 

Liquid means a substance or mixture which:  

(i) at 50 °C has a vapour pressure of not more than 300 kPa (3 bar); 

(ii) is not completely gaseous at 20 °C and at a standard pressure of 101,3 kPa; and 

(iii) which has a melting point or initial melting point of 20 °C or less at a standard pressure 
of 101,3 kPa; 

Solid means a substance or mixture which does not meet the definitions of liquid or gas. 

In  some  cases  (such  as  viscous  substances  or  mixtures),  a  specific  melting  point  cannot  be 
determined. Such a substance or mixture must be regarded as a liquid if either the result of the 
ASTM International14 D4359-90 test (standard test method for determining whether a material is 
a liquid or a solid) indicates ‘liquid’ or the result of the test for determining fluidity (penetrometer 
test)  prescribed  in  section  2.3.4  of  Annex  A  of  the  European  Agreements  on  the  international 
transport of dangerous goods by road indicates ‘not pasty’. As mentioned in section 1.2, the same 
solid  substance  or  mixture  may  have  different  forms  such  as  flakes,  prills,  or  powder. 
Furthermore, a powder may contain particles of different size, and particles of the same size may 
have  different  shapes,  crystallinity  or  allotropy  etc.  These  differences  may  result  in  different 
intrinsic properties, and consequently, different physical hazards of the powder. Particle size is 
crucial  for  several  hazard  classes  such  as  explosives,  flammable  solids,  solid  self-reactive 
substances and mixtures, pyrophoric solids, self-heating substances and mixtures, solid organic 
peroxides and solid substances and mixtures which in contact with water emit flammable gases. 
Therefore, besides the physical state other parameters should also be considered when identifying 
the form, since they may trigger different classifications of the same substance or mixture. 

13 CLP, Articles 5(1), 6(1) and 8(6). 

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An example of differing classifications due to different intrinsic properties of substance forms is 
the  allotropes  red  phosphorus  (flammable  solid)  and  white  phosphorus  (pyrophoric  solid). 
Consequently,  it  is  important  to  evaluate  case  by  case  whether  available  information  on  the 
physical  properties  of  the  substance  or  mixture  as  placed  on  the  market  is  applicable  to  the 
examined form, and whether additional testing should be performed. 

The form of a substance or mixture as placed on the market might be such that it is not possible 
to  test  it  in  this  form,  e.g.  if  it  is  in  the  form  of  tablets  or  pellets.  In  such  cases,  the  physical 
hazards  of  the  substance  or  mixture  in  its  granular/powdered  form  should  be  considered  for 
classification, especially if it is friable and produces secondary effects due to abrasion or crushing 
during supply and use. If phase separation occurs, the most hazardous properties of each phase 
of the substance or mixture must be communicated.  

If  further  testing  is  required,  the  choice  of  the  test  method  should  be  done  after  thorough 
evaluation  of  its  suitability  for  the  substance  or  mixture,  as  the  properties  of  the  form  (e.g. 
powders particle size and shape) may have a significant effect on the test results. 

2.0.5  Quality 

The determination of data must be based on the methods named in CLP Annex I, Part 2. Whenever 
possible, the laboratory should regularly assess its performance with respect to the methods used, 
e.g.  by  participating  in  inter-laboratory  testing  or  by  using  reference  materials.  Any  deviation 
from the test procedure or standard should be documented and, if necessary, justified. 

The reliability of all test results used for the classification of hazardous substances and mixtures 
is important so their transparency and comparability must be ensured. 

For these purposes, CLP requires in Article 8 the following: 

Article 8(5) 

Where new tests for physical hazards are carried out for the purposes of this Regulation, they 
shall be carried out, at the latest from 1 January 2014, in compliance with a relevant 
recognised quality system or by laboratories complying with a relevant recognised standard. 

In general, the following alternative strategies can be pursued: 

1.  Compliance with the principles of good laboratory practice (GLP); 

2.  Application of EN ISO15/IEC16 17025:201717 General requirements for the competence of 

testing and calibration laboratories as a relevant recognised standard; 

3.  Other internationally recognised standards of comparable scope. 

Any laboratory that carries out physical hazard tests for classification purposes can choose from 
these alternatives how to fulfil the quality requirements of CLP. However, it should be noted that 
GLP is not primarily aimed at physical hazard testing and can only be applied to some physical 
hazard test methods. Therefore, in general EN ISO/IEC 17025 is more suitable or preferred over 
GLP for physical hazard testing. 

15 EN ISO: European Union International Organization for Standardisation 

16 IEC: International Electrotechnical Commission 

17 Hereafter: ISO/IEC 17025 

 
 
 
 
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2.1.  EXPLOSIVES 

2.1.1. 

 Introduction 

The requirements in part 2.1 ‘Explosives’ of Annex I of CLP are identical to those in chapter 2.1 
of GHS up to revision 818. However, as of revision 9 of GHS the classification system for explosives 
has been completely altered. It is expected that this new classification system for explosives will 
be included in CLP, upon which this guidance chapter will have to be substantially reviewed.  

Up to revision 8 of GHS, the GHS classification of explosives is almost entirely adopted based on 
the UN Recommendations on the Transport of Dangerous Goods – Model Regulations (UN RTDG 
Model Regulations). This classification system, which is currently used in CLP, is appropriate for 
transport and also for storage of explosives in the transport configuration (e.g. as packaged for 
transport).  In  practice,  the  transport  classification  normally  is  simply  translated  into  the 
corresponding CLP classification without further testing. Note that GHS revision 7 introduced the 
new hazard class ‘desensitised explosives’ which is dealt with separately in section 2.17. 

The changes in the classification system as of GHS revision 9 were introduced to better reflect 
the  explosive  behaviour  when  the  substance,  mixture  or  article  is  not  in  the  transport 
configuration. While the overall scope of the class of explosives was retained, new categories 1 
and 2A-C were introduced to supplement the divisions used for transport and for classification up 
to GHS revision 8. For explosives which are transported (which should be virtually all commercial 
explosives), it is quite straight-forward to derive the new GHS classification from the transport 
classification. 

It should be noted that the explosives hazard class, unlike other hazard classes of CLP, includes 
articles.  According  to  Article  4(8)  of  CLP,  these  articles  should  be  treated  as  substances  and 
mixtures in the context of CLP. 

The classification of substances, mixtures and articles in the explosives hazard class and further 
allocation  to  a  division  is  a  very  complex  procedure.  References  to  Part  I  of  the  UN-MTC  and 
related expertise are necessary. 

2.1.2. 

 Definitions and general considerations for classification of explosives 

The following definition is given in CLP for the class of explosives. 

Annex I: 2.1.1.1. 

The class of explosives comprises 

(a)  explosive substances and mixtures; 

(b)  explosive articles, except devices containing explosive substances or mixtures in such 
quantity or of such a character that their inadvertent or accidental ignition or initiation 
shall not cause any effect external to the device either by projection, fire, smoke, heat 
or loud noise; and 

(c) 

substances, mixtures and articles not mentioned in points (a) and (b) above which are 
manufactured with the view to producing a practical, explosive or pyrotechnic effect. 

Additional  remark  related  to  the  applicability  of  2.1.1.1(a)  (see  also  the  UN  RTDG  Model 
Regulations, section 2.1.1.1(a)): 

18 The twelfth ATP (Commission Regulation (EU) 2019/521) implements the changes introduced by the sixth (2015) and 
seventh (2017) revisions of the GHS into the CLP Regulation. No changes on chapter 2.1 were included in GHS revision 
8. Consequently, if not specified “GHS” indicates “GHS revision 7”. 

 
 
 
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•  a substance  or mixture which is not itself an explosive (i.e. it does not react  out of the 
condensed phase), but which can form an explosive atmosphere of gas, vapour or dust is 
not included in this class; 

•  explosive behaviour of organic peroxides and of self-reactive substances and mixtures is 
covered  by  those  specific  hazard  classes  and  therefore  not  included  in  the  hazard  class 
explosives. 

In addition, the following definitions from CLP apply for explosives:  

Annex I: 2.1.1.2. 

For the purposes of this Regulation the following definitions shall apply: 

An explosive substance or mixture is a solid or liquid substance or mixture of substances 
which is in itself capable by chemical reaction of producing gas at such a temperature and 
pressure and at such a speed as to cause damage to the surroundings. Pyrotechnic 
substances are included even when they do not evolve gases. 

A pyrotechnic substance or mixture is a substance or mixture of substances designed to 
produce an effect by heat, light, sound, gas or smoke or a combination of these as the result 
of non-detonative self-sustaining exothermic chemical reactions. 

An unstable explosive is an explosive which is thermally unstable and/or too sensitive for 
normal handling, transport and use. 

An explosive article is an article containing one or more explosive substances or mixtures. 

A pyrotechnic article is an article containing one or more pyrotechnic substances or mixtures. 

An intentional explosive is a substance, mixture or article which is manufactured with a view 
to produce a practical explosive or pyrotechnic effect. 

2.1.3. 

 Relation to other physical hazards 

Substances,  mixtures  or  articles  which  have  already  been  classified  as  explosives  (Class  1 
according to the UN RTDG Model Regulations) should normally not be considered for classification 
in any other physical hazard classes, as the explosion hazard can be considered to be the most 
severe of the physical hazards. Furthermore, testing explosives for other physical hazards may 
pose a severe safety concern for the testing personnel, which must always be avoided. 

When considering substances and mixtures for classification within the hazard class explosives, 
the following checks should be performed with respect to other hazard classes: 

−  Substances, mixtures and articles that have been manufactured with a view to producing 
a  practical  explosive  or  pyrotechnic  effect,  are  classified  as  explosives  by  definition 
according to 2.1.1.1(c) of Annex I of CLP. It should be checked whether such a substance 
or mixture is an unstable explosive. 

−  Thermally unstable substances or mixtures that are not classified as explosives should be 

considered for classification as self-reactive substances and mixtures. 

−  Mixtures  of  oxidising  substances  and  mixtures  with  combustible  material  that  are  not 
classified as explosives should be considered for classification as self-reactive substances 
and mixtures, oxidising liquids or oxidising solids. 

−  Explosive  substances  or  mixtures  may  be  phlegmatised  such  that,  in  the  phlegmatised 
state,  they  meet  the  criteria  for  classification  as  desensitised  explosives  and  should  be 
classified as such instead of as explosives. 

Due to the complexity of these issues, expert advice should always be sought when dealing with 
classification of substances and mixtures and articles with potentially explosive properties. 

 
 
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2.1.4. 

 Classification of substances, mixtures or articles as explosives 

2.1.4.1. 

Identification of hazard information 

Information  on  the  following  types  of  hazards  is  relevant  for  the  evaluation  of  substances, 
mixtures and articles for the class of explosives: 

• 

sensitivity to shock; 

•  effects of heating and ignition under confinement; 

• 

• 

thermal stability; 

sensitiveness to impact and friction; 

•  mass explosion hazard; 

•  projection hazard; 

• 

fire and radiant heat hazard. 

2.1.4.2. 

Screening procedures and waiving of testing 

The screening procedure is described in CLP Annex I, sections 2.1.4.2 and 2.1.4.3 with references 
to Appendix 6 of the UN-MTC. 

The screening procedure may be used for substances or mixtures which are suspected of having 
explosive  properties.  It  is  not  applicable  to  substances  and  mixtures  manufactured  with  the 
intention  of  producing  a  practical  explosive  or  pyrotechnic  effect,  as  these  are  classified  as 
explosives by definition. 

Explosive properties are associated with the presence of certain chemical groups in a molecule 
which can react to produce very rapid increases in temperature and/or pressure. The screening 
procedure is aimed at identifying the presence of such reactive groups and the potential for rapid 
energy release.  

Examples of groups which may indicate explosive properties in organic materials are: 

•  C-C unsaturation (e.g., acetylenes, acetylides, 1, 2-dienes); 

•  C-Metal, N-Metal (e.g., Grignard reagents, organo-lithium compounds); 

•  Contiguous nitrogen atoms (e.g., azides, aliphatic azo compounds, diazonium salts, 

hydrazines, sulphonylhydrazides); 

•  Contiguous oxygen atoms (e.g., peroxides, ozonides); 

•  N-O (e.g. hydroxyl amines, nitrates, nitro compounds, nitroso compounds, N-oxides, 

1,2-oxazoles); 

•  N-halogen (e.g., chloramines, fluoroamines); 

•  O-halogen (e.g., chlorates, perchlorates, iodosyl compounds). 

A substance or mixture does not have to undergo the acceptance procedure, and is therefore not 
classified as explosive, if: 

a.  There are no chemical groups associated with explosive properties present in the molecule 

(see listing above for indications of chemical groups); 

or 

b.  The substance or mixture contains chemical groups associated with explosive properties 

which include oxygen and the calculated oxygen balance is less than -200; 

 
 
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The oxygen balance is calculated for the chemical reaction: 

 

Using the formula: 

Oxygen balance = 

24 

or 

c.  For an organic substance or a homogenous mixture of organic substances, containing one 

or more chemical group(s) associated with explosive properties: 

− 

− 

the exothermic decomposition energy is less than 500 J/g; or 

the onset of exothermic decomposition is 500 ºC or above, as indicated in CLP, Annex 
I, Table 2.1.3 (see below). 

(The temperature limit is to prevent the procedure being applied to a large number of 
organic materials which are not explosive, but which will decompose slowly above 500 
ºC to release more than 500 J/g. Therefore, the measurement is not normally carried 
out beyond 500 ºC). The exothermic decomposition energy may be determined using 
a suitable calorimetric technique see section 20.3.3.3 of the UN-MTC. 

Annex I: Table 2.1.3 
class ‘Explosives’ for an organic substance or a homogenous mixture of organic 
substances 

Decision to apply the acceptance procedure for the hazard 

Decomposition energy 

Decomposition onset 
temperature 

(J/g) 

< 500 

< 500 

≥ 500 

≥ 500 

(°C) 

< 500 

≥ 500 

< 500 

≥ 500 

Apply acceptance procedure? 

(Yes/No) 

No 

No 

Yes 

No 

or 

d.  for mixtures of inorganic oxidising substances with organic material(s), the concentration 

of the inorganic oxidising substance is: 

• 

• 

less than 15 % by mass, if the oxidising substance is assigned to categories 1 or 2; 

less than 30 % by mass, if the oxidising substance is assigned to category 3. 

If the screening procedure identifies the substance or mixture to be a potential explosive or if it 
is a mixture containing any known explosives, the classification (acceptance) procedure for the 
class of explosives (see section 2.1.4.5) has to be applied. If the exothermic decomposition energy 
of organic materials is less than 800 J/g, a UN gap test is not required, neither according to Series 
1 Type (a) nor according to Series 2 Type (a). 

Note:  If  explosive  properties  cannot  be  rules  out  according  to  the  above  screening  procedure, 
testing  is  required  (at  least  Test  Series  2  of  the  UN-MTC)  unless  another  valid  scientific 

OOHC2zyx2z4yx−++OHCO222yx+()weightmolecular z2yx21600−+− 
 
 
 
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25 

argumentation is given. EU Test A.14 cannot be used to conclude on classification, including ‘no 
classification’. 

2.1.4.3. 

Classification criteria 

The criteria for the classification of explosives are given in the following tables. 

Annex I:  

2.1.2.1. Substances, mixtures and articles of this class are classified as an unstable explosive 
on the basis of the flowchart in Figure 2.1.2. The test methods are described in Part I of the 
UN RTDG, Manual of Tests and Criteria. 

2.1.2.2. Substances, mixtures and articles of this class, which are not classified as an unstable 
explosive, shall be assigned to one of the following six divisions depending on the type of 
hazard they present: 

(a) Division 1.1 

Substances, mixtures and articles which have a mass explosion hazard 

(a mass explosion is one which affects almost the entire quantity present virtually 
instantaneously); 

(b) Division 1.2 

Substances, mixtures and articles which have a projection hazard but 

not a mass explosion hazard; 

(c) Division 1.3 

Substances, mixtures and articles which have a fire hazard and either a 

minor blast hazard or a minor projection hazard or both, but not a mass explosion 
hazard: 

(i) 

combustion of which gives rise to considerable radiant heat; or 

(ii) 
both; 

which burn one after another, producing minor blast or projection effects or 

(d) Division 1.4 

Substances, mixtures and articles which present no significant hazard: 

−  substances, mixtures and articles which present only a small hazard in the event of 

ignition or initiation. The effects are largely confined to the package and no projection 
of fragments of appreciable size or range is to be expected. An external fire shall not 
cause virtually instantaneous explosion of almost the entire contents of the package; 

(e) Division 1.5 

Very insensitive substances or mixtures which have a mass explosion 

hazard: 

−  substances and mixtures which have a mass explosion hazard but are so insensitive 

that there is very little probability of initiation or of transition from burning to 
detonation under normal conditions; 

(f) Division 1.6 

Extremely insensitive articles which do not have a mass explosion 

hazard: 

−  articles which predominantly contain extremely insensitive substances or mixtures; 

−  and which demonstrate a negligible probability of accidental initiation or propagation. 

2.1.2.3. Explosives, which are not classified as an unstable explosive, shall be classified in one 
of the six divisions referred to in section 2.1.2.2 of this Annex based on Test Series 2 to 8 in 
Part I of the UN RTDG, Manual of Tests and Criteria according to the results of the tests laid 
down in Table 2.1.1: 

Table 2.1.1 

 
 
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Criteria for explosives 

Category 

Criteria 

Unstable explosives or 
explosives of Divisions 1.1 
to 1.6 

For explosives of Divisions 1.1 to 1.6, the following are the core 
set of tests that need to be performed: 

Explosibility: according to UN Test Series 2 (section 12 of the UN 
RTDG, Manual of Tests and Criteria). Intentional explosives (¹) 
shall not be subject to UN Test Series 2. 

Sensitiveness: according to UN Test Series 3 (section 13 of the 
UN RTDG, Manual of Tests and Criteria). 

Thermal stability: according to UN Test 3(c) (sub-section 13.6.1 
of the UN RTDG, Manual of Tests and Criteria). 

Further tests are necessary to allocate the correct Division. 

(¹) This comprises substances, mixtures and articles which are manufactured with a view to 
producing a practical, explosive or pyrotechnic effect. 

2.1.4.4. 

Testing and evaluation of hazard information 

Where test data are available, these must be evaluated against the set criteria for classification. 

When  the  screening  procedure  indicates  that  a  substance  or  mixture  may  possess  explosive 
properties, a cautious approach when performing the tests is necessary to ensure safe handling. 

For information on the test procedures see the following section 2.1.4.5 where the individual test 
series are described in context with the respective decision logic. 

The test procedures for the classification of explosives are described in detail in the Part I of the 
UN-MTC. 

Where the test is conducted in the packaged form and the packaging is changed, a further test 
must be conducted where it is considered that the change in packaging will affect the outcome of 
the test. 

Classification  tests  must  be  performed  on  the  substance  or  mixture  as  supplied.  If  the  same 
chemical is to be presented in a physical form different from that which was tested and which is 
considered  likely  to  materially  alter  its  performance  in  a  classification  test,  the  substance  or 
mixture must also be tested in the new form, where possible. 

2.1.4.5. 

Classification procedure and decision logics 

Any substance, mixture or article having, or suspected of having, explosives characteristics must 
be considered for classification in the explosives hazard class. Substances, mixtures and articles 
classified in this hazard class must be assigned to the appropriate division or must be classified 
as unstable explosive. 

It  should  be  noted  that,  as  a  consequence  to  the  substantial  changes  to  the  explosives 
classification  procedure  as  GHS  revision  9  (see  introduction,  section  2.1.1),  the  UN-MTC  was 
consequently  amended19.  In  essence,  the  amendments  mean  that  all  references  to  “unstable 
explosive”  and  to  “too  dangerous  for  transport”  in  the  UN-MTC  have  been  replaced  by  “too 

19 These amendments are included in revision 7/amendment 1 of the UN-MTC. 

 
 
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sensitive to assign a division”. A substance, mixture or article that is considered “too sensitive to 
assign a division” according to the UN-MTC is classified as an unstable explosive according to CLP. 

The  classification  procedure  is  divided  into  two  stages,  the  acceptance  procedure  and  the 
assignment procedure.  

In the acceptance procedure, intrinsic explosive properties of a substance, mixture or article are 
determined  through  tests  of  its  sensitivity,  stability  and  explosion  effects.  If  the  substance, 
mixture or article is not characterised as unstable explosive and is provisionally accepted into the 
class  of  explosives,  it  is  then  necessary  to  ascertain  the  correct  division  by  applying  the 
assignment  procedure.  The  further  subdivision  into  compatibility  groups  A  to  S  is  described  in 
detail in the UN-MTC, section 2.1.2. The compatibility groups and their recommended combination 
identify  types  of  explosives  which  are  deemed  to  be  compatible,  e.g.  for  combined  storage  or 
transportation and can subsequently be used to distinguish technical requirements (especially) in 
these sectors. However, assignment of compatibility groups is not part of the classification system 
according to CLP. 

The tests for acceptance and the further tests to determine the correct division are grouped into 
eight  test  series.  Classification  procedures,  test  methods  and  criteria  are  described  in  detail  in 
Part I of the UN-MTC. 

NOTE: The person responsible for the classification of explosives should be experienced in 
this field and be familiar with the criteria for classification. 

2.1.4.5.1. 

Acceptance procedure 

The  acceptance  procedure  is  used  to  determine  whether  a  substance,  mixture  or  article  is  a 
candidate for the class of explosives, and whether it is an unstable explosive (which is not allowed 
for transport). 

The  test  methods  used  for  deciding  on  provisional  acceptance  into  the  class  of  explosives  are 
grouped into four series, Test Series 1 to 4 (see CLP Annex I, Figure 2.1.2 reported below). 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Annex I: Figure 2.1.2 
mixture or article in the class of explosives (Class 1 for transport) 

Procedure for provisional acceptance of a substance, 

The numbering of Test Series 1 to 4 relates to the sequence of assessing the results rather than 
the order in which the tests should be conducted. It may be important for the safety of test 

 
 
 
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personnel that certain tests, using small amounts of material, are conducted first before 
proceeding to experiment with larger quantities.  

Starting  the  testing  procedure  with  Test  Series  3  is  highly  recommended,  because  these  tests 
involve relatively small sample sizes, which reduces the risk to test personnel. While Test Series 
1  may  be  waived  for  the  purpose  of  classification,  it  can  provide  useful  information  on  the 
properties of the substance or mixture. 

Test Series 1 

Within Test Series 1 the question ‘Is it an explosive substance / mixture?’ is answered on the 
basis of the results of three types of tests to assess possible explosive effects. The question is 
answered ‘Yes’ if a ‘+’ is obtained in any of the three types of tests. If the answer is ‘No’, the 
substance / mixture is rejected from this class; it is not an explosive. Under certain conditions 
the  Test  Type  1  (a)  can  be  replaced  by  certain  tests  of  Test  Series  F,  see  UN-MTC,  section 
11.3.5.  

The three types of test used are (recommended test is indicated within brackets): 

Type 1 (a): 

a shock test with defined booster and confinement to determine the ability 
of the substance to propagate a detonation (UN Gap test, zero gap); 

Type 1 (b): 

a test to determine the effect of heating under confinement (Koenen test); 
and 

Type 1 (c): 

a test to determine the effect of ignition under confinement (time/pressure 
test). 

Test Series 2 

Series 2 tests are used to answer the question ‘Is the substance / mixture too insensitive for 
acceptance into this Class?’. In general, the basic apparatus and method used is the same as 
that for Test Series 1 but with less stringent criteria, e.g. in the case of gap tests, the gap used 
is greater than zero. The question is answered ‘No’ if a ‘+’ is obtained in any of the three types 
of test. If the answer is ‘Yes’, the substance / mixture is rejected from this class; it is not an 
explosive. Under certain  conditions Test Type  2 (a) can be replaced by certain tests of Test 
Series F, see UN-MTC, section 12.3.4. 

The following three types of test are used (recommended test is indicated within brackets): 

Type 2 (a): 

a  shock  test  with  defined  initiation  system  and  confinement  to  determine 
sensitivity to shock (UN gap test) (with a defined gap e.g. 50 mm); 

Type 2 (b): 

a test to determine the effect of heating under confinement (Koenen test); 
and 

Type 2 (c): 

a test to determine the effect of ignition under confinement (Time/pressure 
test). 

If the substance  or mixture is manufactured with a view to produce a  practical explosive  or 
pyrotechnic  effect,  it  is  unnecessary  to  conduct  Test  Series  1  and  2  for  purposes  of 
classification. 

Test Series 3 

As stated above, it is recommended to carry out Test Series 3 before Test Series 1 and 2 for 
safety reasons due to the small sample amount needed. It is also recommended to carry out 
Test Series 3 even if negative results have been obtained in Test Series  1 and/or 2 because 
only  Test  Series  3  gives  information  about  the  thermal  stability  and  the  sensitivity  to 
mechanical stimuli (impact and friction). 

Test Series 3 is used to answer the questions ‘Is the substance or mixture thermally stable?’ 
and ‘Is the substance / mixture too dangerous in the form in which it was tested (and therefore 

 
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unstable in that form)?’20 This involves tests for determining the sensitiveness of the substance 
or mixture to mechanical stimuli (impact and friction), and to heat and flame.  

The following four types of tests are used (recommended test is indicated within brackets): 

Type 3 (a): 

a  falling  weight  test  to  determine  sensitiveness  to  impact  (BAM 
Fallhammer); 

Type 3 (b): 

a  friction;  or  impacted  friction  test  to  determine  sensitiveness  to  friction 
(BAM friction apparatus); 

Type 3 (c): 

an  elevated  temperature  test  to  determine  thermal  stability  (thermal 
stability test at 75 °C); and 

Type 3 (d): 

an ignition test to determine the response of a substance or mixture to fire 
(small scale burning test). 

The first question is answered ‘No’ if a ‘+’ is obtained in Test Type 3 (c). Then the substance / 
mixture is considered as thermally unstable and either classified as an unstable explosive or 
as a self-reactive substance or mixture.  

The second question is answered ‘Yes’ if a ‘+’ is obtained in any of the Test Types 3 (a), 3 (b) 
or  3  (d).  If  a  ‘+’  is  obtained,  the  substance  /  mixture  may  be  encapsulated  or  packaged  to 
reduce  its  sensitiveness  to  external  stimuli  or  is  classified  as  an  unstable  explosive. 
Furthermore, the explosive may be desensitised to suppress/reduce its explosive properties in 
which case the classification procedure has to be restarted.  

Test Series 4 

Series 4 tests are intended to answer the question ‘Is the article, packaged article or packaged 
substance  or  mixture  too  dangerous  (and  therefore  an  unstable  explosive)?’21.  Conditions 
which  may  occur  during  supply  and  use  include  high  /  low  temperature  and  high  relative 
humidity, vibration, bumping and dropping.  

The two types of test to be carried out are: 

Type 4 (a): 

a test of thermal stability for articles; and 

Type 4 (b): 

a test to determine the hazard from dropping. 

The question is answered ‘Yes’ if a ‘+’ is obtained in either Test Type 4 (a) or 4 (b) and the 
substance or mixture or article is classified as an unstable explosive. 

It  is  important  to  note  that  a  substance  /  mixture  which  fails  Test  Series  2  (i.e.  it  is  sensitive 
enough for acceptance into the class of explosives) may still, if properly packaged, leave the class 
of explosives provided that it is not designed to have an explosive effect and does not exhibit any 
explosive hazard in Test Series 6 of the assignment procedure (see example for musk xylene). 
Such an exclusion from the class of explosives is restricted to the specific type and size of package 
tested. 

Especially for substances / mixtures, which have explosive properties according to Test Series 1 
and/or 2 but can leave the class of explosives after Test Series 6 due to the type of packaging; 
these properties should be communicated in the Safety Data Sheet (SDS).  

2.1.4.5.2. 

Assignment procedure to a division 

The assignment procedure to  one  of six divisions, depending on the type of hazard presented, 
applies to all substances, mixtures and/or articles that are candidates for the class of explosives. 

20 Through UN-MTC revision 7/ amendment 1, this question has been changed to “Is the substance / mixture too sensitive 
to assign a division?”, see the introduction to section 2.1.4.5. 

21  Through  UN-MTC  revision  7/  amendment  1,  this  question  has  been  changed  to  “Is  the  article,  packaged  article  or 
packaged substance or mixture too sensitive to assign a division”, see the introduction to section 2.1.4.5. 

 
 
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A substance, mixture or article must be assigned to the division which corresponds to the results 
of the tests to which the substance, mixture or article, as presented for supply and use, has been 
subjected. Other test results, and data gathered from accidents which have occurred, may also 
be taken into account.  

The test methods used for assignment to a division are grouped into three series – Test Series 5 
to 7 – designed to provide the information necessary to answer the questions in Figure 2.1.3 in 
CLP. 

  NOTE: The person responsible for the classification of explosives should be experienced in 

this field and be familiar with the criteria for classification. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Annex I: Figure 2.1.3 
explosives (Class 1 for transport) 

Procedure for assignment to a division in the class of 

 
 
 
 
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Test Series 5 

Test Series 5 is only carried out for explosive substances / mixtures which are very insensitive 
and consequent candidates for division 1.5. Typical substances / mixtures are blasting agents 
such as ammonium nitrate / fuel oil (ANFO), slurries, and emulsion explosives. 

The  results  from  three  types  of  series  5  tests  are  used  to  answer  the  question  ‘Is  it  a  very 
insensitive explosive substance / mixture with a mass explosion hazard?’.  

The test types are (recommended test is indicated within brackets): 

Type 5 (a):  a shock test to determine the sensitivity to intense mechanical stimulus (cap 

sensitivity test); 

Type 5 (b):  thermal  tests  to  determine  the  tendency  of  transition  from  deflagration  to 

detonation (French or USA DDT test); and 

Type 5 (c):  a  test  to  determine  if  a  substance,  when  in  large  quantities,  explodes  when 

subjected to a large fire. 

The question is answered ‘No’ if a ‘+’ is obtained in any of the three test types. A candidate for 
Division 1.5 should pass one test of each type. 

Test Series 6 

The results from four types of series 6 tests are used to determine which division, amongst 
Divisions 1.1, 1.2, 1.3 and 1.4, corresponds most closely to the behaviour of the substance, 
mixture or article to be classified if a load is involved in a fire resulting from internal or external 
sources or an explosion from internal sources. The results are also necessary to assess whether 
a substance, mixture or article can be assigned to Compatibility Group S of Division 1.4 and 
whether or not it may be excluded from this class. Test Series 6 should be applied to packages 
of  substances,  mixtures  or  articles  in  the  condition  and  form  in  which  they  are  offered  for 
supply and use. 

The four test types are (recommended test is indicated within brackets): 

Type 6 (a):  a  test  on  a  single  package  to  determine  if  there  is  mass  explosion  of  the 

contents (single package test); 

Type 6 (b):  a test on packages of an explosive substance, mixture or explosive articles, or 
non-packaged  explosive  articles,  to  determine  whether  an  explosion  is 
propagated  from  one  package  to  another  or  from  a  non-packaged  article  to 
another (stack test);  

Type 6 (c):  a test on packages of an explosive substance, mixture or explosive articles, or 
non-packaged  explosive  articles,  to  determine  whether  there  is  a  mass 
explosion or a hazard from dangerous projections, radiant heat and/or violent 
burning or any other dangerous effect when involved in a fire (bonfire test); 

Type 6 (d):  a test on an unconfined package of explosive articles to which special provision 
347 of chapter 3.3 of the UN RTDG Model Regulations applies, to determine if 
there are hazardous effects outside the package arising from accidental ignition 
or initiation of the contents.  

Test Types 6 (a), 6 (b), 6 (c) and 6 (d) are performed in alphabetical order. However, it is not 
always  necessary  to  conduct  tests  of  all  types.  Test  Type  6  (a)  may  be  waived  if  explosive 
articles are carried without packaging or when the package contains only one article. Test Type 
6 (b) may be waived if in each Type 6 (a) test: 

• 

• 

the exterior of the package is undamaged by internal detonation and/or ignition; or 

the  contents  of  the  package  fail  to  explode  or  explode  as  feebly  as  would  exclude 
propagation of the explosive effect from one package to another in Test Type 6 (b). 

 
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Test  Type  6  (c)  may  be  waived  if,  in  a  Type  6  (b)  test,  there  is  practically  instantaneous 
explosion of virtually the total contents of the stack. In such cases the product is assigned to 
Division 1.1. 

Test  Type  6  (d)  is  a  test  used  to  determine  whether  a  Division  1.4  compatibility  group  S 
classification is appropriate and is only used if special provision 347 of chapter 3.3 of the UN 
RTDG Model Regulations applies. The results of Test Series 6 (c) and 6 (d) indicate if division 
1.4  compatibility  group  S  is  appropriate,  otherwise  the  classification  is  Division  1.4, 
compatibility group other than S. 

If a substance or mixture gives a ‘—‘ result (no propagation of detonation) in the Series 1 Type 
(a) test, the 6 (a) test with a detonator may be waived.  

If a substance gives a ‘—‘ result (no or slow deflagration) in a Series 2 Type (c) test, the Test 
Type 6 (a) test with an igniter may be waived. 

Test Series 7 

Test  Series  7  aims  at  military  explosives  (Extremely  Insensitive  Substance  (EIS)  or  article 
containing  an  EIS)  and  is  generally  not  relevant  for  explosives  for  civil  use.  Therefore,  the 
individual tests are not described here. If needed, they can be found  in the UN-MTC, Part I, 
section 17. 

Test Series 8 

The question whether a candidate for ammonium nitrate emulsion or suspension or gel (ANE), 
intermediate  for  blasting  explosives  is  insensitive  enough  for  classification  as  oxidising  is 
answered by Test Series 8.  

According to CLP, there are three test types for ANE (recommended test is indicated within 
brackets): 

Type 8 (a):  a test to determine the thermal stability (Thermal Stability Test for ANE); 

Type 8 (b):  a shock test to determine sensitivity to intense shock (ANE gap test);  

Type 8 (c):  a test to determine the effect of heating under confinement (Koenen test). 

Test Series 8 is used to establish whether an ANE may leave the class of explosives or not. 
ANE:s  that  are  allowed  to  leave  the  class  of  explosives  are  classified  as  oxidising  liquids  or 
oxidising solids (depending on their viscosity).  

In  the  UN-MTC  there  is  an  additional  classification  Test  Type  8  (e)  (the  Minimum  Burning 
Pressure test), which has not yet been introduced into the CLP classification scheme.  

Test Type 8 (d) of the UN-MTC is not used for classification and has no relevance for CLP. 

Annex I: Figure 2.1.4 
emulsion, suspension or gel (ANE) 

Procedure for the classification of ammonium nitrate 

 
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2.1.5.  Hazard communication for explosives 

2.1.5.1. 
statements22 

Pictograms, signal words, hazard statements and precautionary 

Annex I: Table 2.1.2 

Label elements for explosives 

Classification 

Unstable 
Explosive 

Division 1.1  Division 1.2  Division 1.3  Division 1.4  Division 1.5  Division 1.6 

GHS 
Pictograms 

Signal Word 

Danger 

Danger 

Danger 

Danger 

Warning 

Danger 

Hazard 
Statement 

H200: 
Unstable 
Explosive 

H201: 
Explosive; 
mass 
explosion 
hazard 

H202: 
Explosive; 
severe 
projection 
hazard 

H203: 
Explosive; 
fire, blast or 
projection 
hazard 

H204: Fire 
or 
projection 
hazard 

H205: May 
mass 
explode in 
fire 

Pre-
cautionary 
Statement 
Prevention 

P201 

P250 

P280 

P210 

P230 

P234 

P240 

P250 

P280 

P210 

P230 

P234 

P240 

P250 

P280 

P210 

P230 

P234 

P240 

P250 

P280 

Pre-
cautionary 
Statement 
Response 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P372 + 
P380 + 
P373 

P210 

P234 

P240 

P250 

P280 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P380 + 
P375 

P210 

P230 

P234 

P240 

P250 

P280 

No signal 
word 

No hazard 
statement 

No pre-
cautionary 
statement 

P370 + 
P372 + 
P380 + 
P373 

No pre-
cautionary 
statement 

Pre-
cautionary 
Statement 
Storage 

Pre-
cautionary 
Statement 
Disposal 

P401 

P401 

P401 

P401 

P401 

P401 

P501 

P501 

P501 

P501 

P501 

P501 

No pre-
cautionary 
statement 

No pre-
cautionary 
statement 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

The  intrinsic  explosive  properties  of  substances  and  mixtures  regarding  their  stability  and 
sensitivity are only investigated within Test Series 1, 2 and 3 during the acceptance procedure. 
Subsequent tests for the assignment to the Divisions 1.1, 1.2, 1.3  and 1.4 (Test Series 6) are 

22 The combination statement P370+P372+P380+P373 applies to Division 1.4 except for compatibility group S in transport 
packaging,  whereas  the  combination  statement  P370+P380+P375  applies  to  Division  1.4  compatibility  group  S  in 
transport packaging. 

 
 
 
 
 
 
 
 
 
 
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carried  out  with  the  packaged  substances,  mixtures  or  articles.  The  type  of  packaging  may 
significantly influence the test outcome. 

Consequently, there are some deficiencies in the hazard communication of GHS for unpacked or 
repacked explosive substances and mixtures, especially for substances and mixtures, which are 
provisionally accepted in the class of explosives but are later rejected from this class due to their 
packaging  in  the  assignment  procedure  (see  CLP  Annex  I,  Figure  2.1.1  and  Figure  2.1.3  and 
section 2.1.4.5). These substances and mixtures have explosive properties but there might be no 
hazard  communication  about  these  properties  due  to  the  subsequent  classification  in  a  hazard 
class other than the class of explosives. Musk xylene is an example which illustrates this issue 
(see section 2.1.7.2). The results of Test Series 6 for musk xylene in the specified packaging led 
to the  exclusion  of this substance from the hazard class  of explosives. But musk xylene on its 
own (unpacked) shows explosive properties due to heating under confinement (Koenen test). Also 
repacking of the substance in a packaging other than the tested one can result in a completely 
different outcome of Test Series 6.  

It is due to this dependence on the transport configuration that the GHS classification of explosives 
has been thoroughly changed as of GHS revision 9, see the introduction (section 2.1.1). 

2.1.5.2. 

Additional labelling provisions 

2.1.5.2.1. 

Packaging dependence 

Explosives are normally classified in their transport packaging. The packaging itself may be crucial 
for the classification. This is clear from the Figure 2.1.3 in section 2.1.4.5 especially when it comes 
to Test Series 6. As such, the assignment of an explosive substance  or mixture to a particular 
division within the hazard class of explosives is only valid for the substance and mixture in the 
packaging  in  which  it  was  tested,  which  is  usually  the  transport  packaging.  Because  of  the 
package-dependence of the classification, CLP Annex I, section 2.1.2.4 prescribes: 

Annex I: 2.1.2.4. If explosives are unpackaged or repacked in packaging other than the 
original or similar packaging, they shall be retested. 

Further, according to NOTE 1 to Table 2.1.2 in CLP Annex I, unpackaged explosives or explosives 
repacked in packaging other than the original or similar packaging must have the following label 
elements: 

Annex I: 2.1.3. 

Hazard communication 

[…] 

NOTE 1: Unpackaged explosives or explosives repackaged in packaging other than the 
original or similar packaging shall include the following label elements: 

(a) 

the pictogram: exploding bomb; 

(b) 

the signal word: ’Danger’; and 

I 

the hazard statement: ‘explosive; mass explosion hazard’ 

Unless the hazard is shown to correspond to one of the hazard categories in Table 2.1.2, in 
which case the corresponding symbol, signal word and/or the hazard statement shall be 
assigned. 

Normally, if explosives are unpackaged or repacked in packaging other than the original or similar 
packaging the classification procedure needs to be performed again to determine which Division 
the explosive belongs to in the new packaging. The label elements prescribed in NOTE 1 to Table 
2.1.2,  as  quoted  above,  are  the  same  as  those  of  Division  1.1  and  in  practice  this  Division 
constitutes the most severe classification of a repackaged explosive. (Please note that Table 2.1.2 

 
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foresees  also  the  hazard  category  ‘unstable  explosive’,  which  is  assigned  on  the  basis  of  the 
intrinsic properties of a substance or mixture via Test Series 3 and it is not package dependent). 
Therefore, CLP allows labelling of a repackaged explosive with labelling corresponding to Division 
1.1  instead  of  retesting.  However,  this  overestimates  the  hazardous  properties  unless  the 
explosive in fact belongs to Division 1.1. 

Many explosives are supplied in inner packages which are placed together in an outer package 
and where the entity as a whole, i.e. the combination of inner and outer packages, constitutes 
the transport packaging. According to the UN RTDG Model Regulations and the modal transport 
regulations  (ADR23,  RID24,  ADN25  and  IMDG26  Code,  ICAO  TI27)  the  classification  tests  are 
performed in the transport packaging. Under Article 33(1) of CLP where the hazard pictograms(s) 
required by CLP relate to the same hazard as in the rules for the transport of dangerous goods, 
the respective CLP hazard pictogram(s) do not need to appear on the outer packaging.  

The classification in accordance with rules on the transport of dangerous goods is almost entirely 
identical to the corresponding classification procedure used in CLP so the CLP classification will 
automatically be known for the transport packaging. However, the CLP classification for the inner 
package alone strictly speaking is not known to the manufacturer, importer or downstream user 
as this will not have been derived from the classification of the transport packaging. On the other 
hand, it is normally not practicable to perform the required tests on the inner packages. Therefore, 
normally  the  same  classification  as  for  the  transport  packaging  may  be  assumed  for  the  inner 
packages. The labelling requirements for the inner packages are those foreseen in Table 2.1.2 of 
CLP Annex I. However, the following exceptions apply: 

•  Transport  packages  in  which  the  packaging  is  designed  such  that  mass  explosion  is 
prevented by the packaging, e.g. by arranging the individual inner packages crosswise (so 
that they are not neighbouring each other) and by separating them with specified material. 
This is especially the case when packing instruction P101 according to section 4.1.5 of the 
ADR applies. In this case the inner package should be labelled in accordance with Note 1 
to Table 2.1.2 of CLP Annex I (i.e. as Division 1.1 unless tested otherwise). 

•  Packages  in  which  explosives  of  different  divisions  are  contained  (for  such  cases  see 
especially the mixed packing provisions MP 20 to MP 24 in section 4.1.10 of the ADR). 

•  Furthermore, they do not apply if the packaging is changed, as stated in Note 1 to Table 

2.1.2 of CLP Annex I. 

2.1.5.2.2. 

Supplemental hazard information 

Risk  phrases  carried  through  from  the  DSD  and  DPD,  but  which  are  not  included  in  GHS,  are 
codified  as  EU  hazard  statements  or  “EUH”.  For  explosive  properties,  EUH044  should  be 
considered. 

Annex II: 

1.1.4. EUH044 – ‘Risk of explosion if heated under confinement’ 

For substances and mixtures not in themselves classified as explosive in accordance with 
section 2.1 of part 2 of Annex I, but which may nevertheless display explosive properties in 
practice if heated under sufficient confinement. In particular, substances which decompose 

23 ADR: Agreement concerning the International Carriage of Dangerous Goods by Road 

24 RID: Regulation concerning the International Carriage of Dangerous Goods by Rail 

25 AND: European Agreement concerning the International Carriage of Dangerous Goods by Inland Waterways 

26 IMDG: International Maritime Dangerous Goods 

27 ICAO TI: International Civil Aviation Organisation Technical Instructions for the Safe Transport of Dangerous Goods by 
Air 

 
 
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39 

explosively if heated in a steel drum do not show this effect if heated in less-strong 
containers. 

Some substances and mixtures which may react explosively if heated under confinement are not 
covered adequately by the classification system. This may e.g. be the case for: 

• 

• 

substances or mixtures which are exempted from the class of explosives based on their 
packaging and according to results of the Test Series 6; 

substances or mixtures with a Self-Accelerating Decomposition Temperature (SADT) of 
more than 75 °C for a 50 kg package which therefore cannot be classified as self-
reactive. 

2.1.5.3. 

Further communication requirements 

According to Note 2 to Table 2.1.2, explosive properties of certain substances and mixtures which 
are exempted from classification as explosives must be communicated to the user via the SDS 
(when one is required). 

Annex I: 2.1.3. 

Hazard communication 

[…] 

NOTE 2: Substances and mixtures, as supplied, with a positive result in Test Series 2 in Part 
I, Section 12, of the UN RTDG, Manual of Tests and Criteria, which are exempted from 
classification as explosives (based on a negative result in Test Series 6 in Part I, Section 16 of 
the UN RTDG, Manual of Tests and Criteria,) still have explosive properties. The user shall be 
informed of these intrinsic explosive properties because they have to be considered for 
handling – especially if the substance or mixture is removed from its packaging or is 
repackaged – and for storage. For this reason, the explosive properties of the substance or 
mixture shall be communicated in Section 2 (Hazards identification) and Section 9 (Physical 
and chemical properties) of the Safety Data Sheet and other sections of the Safety Data 
Sheet, as appropriate. 

2.1.6.  Relation to transport classification 

Division 1.1 – 1.6 within Class 1 of the UN RTDG Model Regulations covers explosive substances, 
mixtures and articles. Normally, the transport classification in accordance with the UN RTDG Model 
Regulations and the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) can 
be  used  one-to-one  when  deriving  the  CLP  classification  for  explosives.  Although,  strictly 
speaking, this classification is only valid for the transport configuration, no re-classification or re-
testing is normally required to derive the corresponding classification according to CLP. See Annex 
I for additional information on transport classification in relation to CLP classification. 

For the use of other packaging or for unpacked substances and mixtures the additional labelling 
provisions (see section 2.1.5.2) have to be observed or re-testing is necessary.  

2.1.7.  Example of classification for explosives 

Examples are given below for the classification of substances. Equivalent information would be 
needed for mixtures.  

2.1.7.1. 
criteria 

Example of substances and mixtures fulfilling the classification 

a.  RESULTS FROM APPLICATION OF THE ACCEPTANCE PROCEDURE 

 
 
40 

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Test  

Conclusion 

Rationale 

0. General data: 

0.1 Name of the substance / 
mixture: Hexanitrostilbene 

1. Is the substance / mixture a candidate 
for ammonium nitrate emulsion, 
suspension or gel, intermediate for 
blasting explosive (ANE)? 

2. Is the substance / mixture 
manufactured with the view to producing a 
practical explosive or pyrotechnic effect? 

3. Test Series 3 

3.1 Thermal stability: 

3.2 Impact sensitivity: 

3.3 Friction sensitivity: 

4. Is the substance / mixture thermally 
stable? 

5. Is the substance / mixture too 
dangerous in the form in which it was 
tested? 

6. Conclusion: 

10.1 Exit: 

No 

Yes 

75 °C / 48-hour 
test (test 3(c)) 

Result: ‘—‘, thermally 
stable 

BAM Fallhammer 
test (Test Type 3 
(a)(ii)) 

BAM friction test 
(Test Type 3 
(b)(i)) 

Result: Limiting 
impact energy 5 J 

Result: Limiting load 
> 240 N 

‘—‘, not too 
dangerous in 
form tested 

‘—‘, not too 
dangerous in 
form tested 

Yes 

No 

PROVISIONALLY 
ACCEPT INTO THIS 
CLASS 

Apply the assignment 
procedure 

b.  RESULTS FROM APPLICATION OF THE ASSIGNMENT PROCEDURE 

Step 

Test 

Conclusion 

Rationale 

1. Is the substance a candidate for 
Division 1.5? 

2. Test Series 6 

No 

Result: Package the 
substance 

2.1 Effect of initiation in the 
package: 

Test 6 (a) with detonator 

Result: detonation, 
crater 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Step 

Test 

Conclusion 

Rationale 

2.2 Effect of propagation: 

Type 6 (b) with detonator 

Result: detonation of 
the whole stack of 
packages, crater 

2.4 Effect of fire engulfment: 

Test 6 (c) may be waived 
because of the result of 
the Test 6 (b). 

3. Is the result a mass explosion? 

Yes 

4. Conclusion: 

Assignment to 
Division 1.1 

2.1.7.2. 
criteria 

Example of substances and mixtures not fulfilling the classification 

This example is taken from the UN-MTC, section 10.5.2, Figure 10.7 (a). 

c.  RESULTS FROM APPLICATION OF THE ACCEPTANCE PROCEDURE 

Step 

Test 

Conclusion 

Rationale 

0. General data: 

0.1 Name of the substance / 
mixture: 5-tert-butyl-2,4,6-
trinitro-m-xylene (musk 
xylene) 

1. Is the substance / mixture a 
candidate for ammonium nitrate 
emulsion, suspension or gel, 
intermediate for blasting explosive 
ANE? 

2. Is the substance / mixture 
manufactured with the view to 
producing a practical explosive or 
pyrotechnic effect? 

3. Test Series 1 

No 

No 

3.1 Propagation of Detonation:  

UN gap test 
(Test 1 (a)) 

Result:’+’, propagation 
of detonation 

3.2 Effect of heating under 
confinement:  

Koenen test 
(Test 1(b)) 

Result: Limiting 
diameter 12.0 mm 

Fragmentation 
type ‘F’ ‘+’, 
shows some 
explosive effects 
on heating 
under 
confinement 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Test 

Conclusion 

Rationale 

3.3 Effect of ignition under 
confinement:  

Time/pressure 
test (test 
1(c)(i)) 

Result: ‘—’, no effect on 
ignition under 
confinement 

4. Is it an explosive substance / 
mixture? 

5.  Test Series 2 

Yes 

5.1 Sensitivity to shock:  

UN gap test 
(Test 2 (a)) 

Result: ‘—’, not 
sensitive to shock 

5.2 Effect of heating under 
confinement:  

Koenen test 
(Test 2 (b)) 

Result: Limiting 
diameter 12.0 mm 

5.3 Effect of ignition under 
confinement:  

Time/pressure 
test (Test 2 
(c)(i)) 

Result: ‘—’, no effect on 
ignition under 
confinement 

6. Is the substance / mixture too 
insensitive for acceptance into this 
class? 

No 

Conclusion:  

7. Test Series 3 

Substance to be 
considered for this class 

7.1 Thermal stability: 

75 °C/48-hour 
test (Test 3 (c)) 

Result: ‘—’, thermally 
stable 

7.2 Impact sensitivity:  

BAM 
Fallhammer test 
(Test 3 (a)(ii)) 

Result: Limiting impact 
energy 25 J", not too 
dangerous in form 
tested. 

Fragmentation 
type ‘F’ ‘+’, 
violent effect on 
heating under 
confinement. 

7.3 Friction sensitivity:  

BAM friction test 
(Test 3 (b)(i)) 

Result: Limiting load > 
360 N 

‘—’, not too 
dangerous in 
form tested 

8. Is the substance / mixture thermally 
stable? 

9. Is the substance / mixture too 
dangerous in the form in which it was 
tested? 

Yes 

No 

10. Conclusion: 

10.1 Exit 

PROVISIONALLY 
ACCEPT INTO THIS 
CLASS 

Apply the assignment 
procedure 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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43 

Step 

Test 

Conclusion 

Rationale 

The explosive properties 
shall be communicated 
in the safety data sheet 
in accordance with 
section 2.1.5.3 above. 

d.  RESULTS FROM APPLICATION OF THE ASSIGNMENT PROCEDURE 

Step 

Test 

Conclusion 

Rationale 

1. Is the substance a candidate for 
Division 1.5? 

No 

Result: Package the 
substance 

2. Test Series 6 

2.1 Effect of initiation in the 
package:  

Test 6 (a) with 
detonator 

2.2 Effect of ignition in the 
package:  

Test 6 (a) with 
igniter 

Result: Only localised 
decomposition around 
detonator 

No significant 
reaction 

Result: Only localised 
decomposition around 
igniter 

No significant 
reaction 

2.3 Effect of propagation:  

Type 6(b) test 
not required as 
no effect outside 
package between 
packages in 6(a) 
test 

2.4 Effect of fire engulfment:  

Test 6 

Result: Only slow 
burning with black 
smoke occurred.  

No effects which 
would hinder fire 
fighting 

3. Is the result a mass explosion? 

4. Is the major hazard that from 
dangerous projections? 

5. Is the major hazard radiant heat 
and/or violent burning but with no 
dangerous blast or projection hazard? 

6. Is there nevertheless a small 
hazard in the event of ignition or 
initiation? 

7. Is the substance manufactured with 
the view to producing a practical 
explosive or pyrotechnic effect? 

No 

No 

No 

No 

No 

8. Conclusion:  

NOT AN EXPLOSIVE 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Test 

Conclusion 

Rationale 

Consider for another 
class (e.g. flammable 
solid) 

 
 
 
 
 
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45 

2.2.  FLAMMABLE GASES  

2.2.1.  Introduction 

The  criteria  for  ‘flammable  gases’  are  found  in  CLP  Annex  I,  section  2.2  and  were  taken  from 
those in chapter 2.2 of GHS18.  

2.2.2.  Definitions and general considerations for classification of flammable 

gases  

Annex I: 2.2.1. 

Definitions 

2.2.1.1 Flammable gas means a gas or gas mixture having a flammable range with air at 
20 °C and a standard pressure of 101.3 kPa. 

2.2.1.2. A pyrophoric gas means a flammable gas that is liable to ignite spontaneously in 
air at a temperature of 54 °C or below. 

2.2.1.3. A chemically unstable gas means a flammable gas that is able to explode even in 
the absence of air or oxygen. 

The flammable range of a flammable gas is the range between its lower explosion limit (LEL) and 
its upper explosion limit (UEL). The term ‘explosion limit’ is synonymous to ‘flammability limit’, 
sometimes used outside the EU. 

2.2.3.  Relation to other physical hazards 

Annex I: 2.2.2. 

Classification criteria 

[…] 

NOTE 1: Aerosols shall not be classified as flammable gases; see Section 2.3. 

NOTE 2: In the absence of data allowing classification into Category 1B, a flammable gas that 
meets the criteria for Category 1A is classified by default in Category 1A. 

For flammable gases that are contained in aerosol dispensers see section 2.3 Aerosols. If classified 
as aerosols, they do not have to be classified as flammable gases in addition. 

In many cases, simultaneous  classification  of gases as  flammable and  gases under pressure is 
applicable, since they are often placed on the marked in pressurised containers. 

Generally, simultaneous classification of gases as flammable and oxidizing is not applicable when 
placed  on  the  market  and  supposed  to  be  transported  (UN  RTDG  Model  Regulations,  section 
2.2.4).  

When a gas mixture contains flammable and oxidizing gases, it can be classified as one of the 
following three categories: 

•  Gases  under  pressure,  if  the  oxygen  content  is  less  than  or  equal  to  23.5  %  and  the 
content of the flammable gases is below the maximum concentration of flammable gas for 
the mixture to be non-flammable or below the lower explosion limit. 

•  Oxidizing, if the oxygen content is more than 23.5 % and the content of the flammable 

gases below the lower explosion limit. 

•  Flammable, if the content of the flammable gases is more than the maximum concentration 
of flammable gas for the mixture to be non-flammable and more than the lower explosion 
limit. 

 
 
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2.2.4.  Classification of substances, mixtures or articles as flammable gases  

2.2.4.1. 

Identification of hazard information 

Many gaseous substances are classified as flammable gases in Annex VI of CLP and more gases 
are classified as flammable gases in the UN RTDG Model Regulations.  

If the classification of flammable gases given in Annex VI of CLP includes the former category 1 
instead of the new categories 1A, 1B, the gas should primarily be classified as 1A, unless there is 
data available justifying 1B. Please refer to Note 2 on CLP Annex I, Table 2.2.1; see also below 
in section 2.2.4.3.  

Please note that the European Industrial Gases Association (EIGA) document 169 applies the new 
criteria  for  a  number  of  flammable  gases  based  on  lower  explosion  limits.  However,  these 
classifications should not be applied if they differ from the classification derived based on the CLP 
criteria, see NOTE 2 in section 2.2.228. 

For gases that are not listed in Annex VI of CLP or in the UN RTDG Model Regulations, there is 
ample scientific literature giving the flammability range for most gases (e.g., ISO 10156:201729 
Gas cylinders — Gases and gas mixtures — Determination of fire potential and oxidizing ability 
for  the  selection  of  cylinder  valve  outlets,  or  BS  EN ISO 80079-20-1:201930,  Explosive 
atmospheres – Part 20-1: Material characteristics for gas and vapour classification – Test methods 
and data). 

Information on gases classified as pyrophoric can be found in chapter 4.2 of EIGA document 169. 

Information on a number of chemically unstable gases can be found in the UN-MTC, section 35. 
Tables  35.1  and  35.2  within  UN-MTC,  section  35.3.2.1  contain  information  on  a  number  of 
chemically unstable gases together with their classification and category.  

To distinguish between the category 1A and 1B, CLP allows the use of lower explosion limit data 
or of fundamental burning velocity data. For information on fundamental burning velocity see ISO 
817:2014  “Refrigerants-Designation  and  safety  classification,  Annex  C:  -  Method  of  test  for 
burning velocity measurement of flammable gases”. 

If no or insufficient information is available, screening and waiving possibilities should be checked. 
Depending on the results, testing might be necessary, see section 2.2.4.4. 

2.2.4.2. 

Screening procedures and waiving of testing 

Gas  mixtures  are  often  prepared  on  demand,  so  there  are  numerous  gas  mixtures  containing 
flammable  gases  on  the  market.  However,  there  are  a  limited  number  of  test  reports  for  the 
flammability of gas mixtures in the scientific literature. Tests are time consuming and expensive. 
In most of the cases, a calculation method as described in ISO 10156 (see section 2.2.4.2) may 
be applied. 

If the calculations in accordance with ISO 10156 show that a gas mixture is not flammable, it is 
also not classified as pyrophoric. Waiving possibilities for pyrophoric gases and chemical instability 
are given in CLP Annex I, sections 2.2.4.3 and 2.2.4.2, respectively. See also waiving possibilities 
for chemically instable gases and gas mixtures given in UN-MTC, section 35. 

28 If there is divergence between the classification in EIGA document 169 and the classification based on Note 2, a CLH 
dossier can be submitted to modify the classification in Annex VI, see ECHA guidance on the preparation of CLH dossier. 

29 Hereafter: ISO 10156 

30 Hereafter: IEC 80079-20-1 

 
 
 
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Annex I: 2.2.4 

Additional Classification Considerations 

2.2.4.3. The classification procedure for pyrophoric gases need not be applied when 
experience in production or handling shows that the substance does not ignite spontaneously 
on coming into contact with air at a temperature of 54 °C or below. Flammable gas mixtures, 
which have not been tested for pyrophoricity and contain more than one percent pyrophoric 
components, shall be classified as a pyrophoric gas. Expert judgement on the properties and 
physical hazards of pyrophoric gases and their mixtures shall be used in assessing the need 
for classification of flammable gas mixtures containing one percent or less pyrophoric 
components. In this case, testing need only be considered if expert judgement indicates a 
need for additional data to support the classification process. 

2.2.4.4. Chemical instability shall be determined in accordance with the method described in 
Part III of the UN RTDG, Manual of Tests and Criteria. If the calculations in accordance with 
ISO 10156 as amended show that a gas mixture is not flammable it is not necessary to carry 
out the tests for determining chemical instability for classification purposes. 

Expert  judgement  should  be  applied  to  decide  whether  a  flammable  gas  or  gas  mixture  is  a 
candidate for classification as chemically unstable to avoid unnecessary testing of gases where 
there is no doubt that they are stable. Functional groups indicating chemical instability in gases 
are triple bonds, adjacent or conjugated double-bonds, halogenated double-bonds and strained 
rings. 

Gas  mixtures  containing  only  one  chemically  unstable  gas  are  not  considered  as  chemically 
unstable and therefore do not have to be tested for classification purposes if the concentration of 
the chemically unstable gas is below the higher of the following generic concentration limits: 

a.  the lower explosion limit (LEL) of the chemically unstable gas; or 

b.  3 mole %. 

Furthermore, for some gases there are also specific concentration limits available and these are 
indicated in Tables 35.1 and 35.2 within UN-MTC, section 35.3.2.1. 

2.2.4.3. 

Classification criteria 

The criteria for the classification of flammable gases are given in the following table: 

Annex I: Table 2.2.1 

Criteria for categorisation of flammable gases 

Category 

Criteria 

Gases, which at 20 °C and a standard pressure of 101.3 kPa are: 

(a) ignitable when in a mixture of 13 % or less by volume in air; or 

Flammable gas 

(b) have a flammable range with air of at least 12 percentage points 

regardless of the lower flammable limit 

1A 

unless data show they meet the criteria for Category 1B 

Pyrophoric gas 

Flammable gases that ignite spontaneously in air at a temperature of 
54 °C or below 

A 

Flammable gases which are chemically unstable at 20 °C and a 
standard pressure of 101.3 kPa 

 
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Chemically 
unstable 
gas 

B 

Flammable gases which are chemically unstable at a temperature 
greater than 20 °C and/or a pressure greater than 101.3 kPa 

1B  Flammable gas 

Gases which meet the flammability criteria for Category 1A, but which 
are not pyrophoric, nor chemically unstable, and which have at least 
either: 

(a) a lower flammability limit of more than 6 % by volume in air; or 

(b) a fundamental burning velocity of less than 10 cm/s; 

2  Flammable gas 

Gases, other than those of Category 1A or 1B, which, at 20 °C and a 
standard pressure of 101,3 kPa, have a flammable range while mixed 
in air. 

[…] 

NOTE 2: In the absence of data allowing classification into Category 1B, a flammable gas that 
meets the criteria for Category 1A is classified by default in Category 1A. 

NOTE 3: Spontaneous ignition for pyrophoric gases is not always immediate, and there may be 
a delay. 

NOTE 4: In the absence of data on its pyrophoricity, a flammable gas mixture shall be classified 
as a pyrophoric gas if it contains more than 1 % (by volume) of pyrophoric component(s) 

2.2.4.4. 

Testing and evaluation of hazard information 

ISO 10156 describes a test method and a calculation method for the classification of flammable 
gas mixtures. The test method may be used in all cases but must be used when the calculation 
method cannot be applied. 

The calculation method applies to gas mixtures and can be applied when the TCi for all flammable 
components and the Kk for all inert components are available. These are listed for a number for 
gases in ISO 10156. In the absence of TCi value for a flammable gas, the value of the LFL can be 
used. In the absence of a Kk value for a non-flammable and non-oxidising gas with three atoms 
or more, a Kk value of 1.5 shall be used. The calculation method described in ISO 10156 uses the 
criterion that a gas mixture is considered non-flammable in air if: 

Equation 2.2.4.4.a   

where: 

Equation 2.2.3.3.b 

and where: 

 is the equivalent content of the i:th flammable gas in the mixture, in % 

1'1=niiciTA==+=pkkkniiiiBKAAA11'iA' 
 
 
 
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 is the maximum content of flammable gas i which, when mixed with nitrogen, is not 

flammable in air, in % 

 is the molar fraction of the i:th flammable gas in the mixture, in % 

 is the molar fraction of the k:th inert gas in the mixture, in % 

 is the coefficient of equivalency of the inert gas k relative to nitrogen 

 is the number of flammable gases in the mixture 

 is the number of inert gases in the mixture 

The principle of the calculation method is the following:  

Where a gas mixture contains an inert diluent other than nitrogen, the volume of this diluent is 
adjusted to the equivalent volume of nitrogen using the equivalency coefficient for the inert gas 

Kk. From this the equivalent contents 
 are then derived through  Equation 2.2.3.3.b, which 
should be viewed as the corresponding concentration of the flammable gases if nitrogen was the 
only  inert  gas  present  in  the  mixture.  In  Equation  2.2.4.4.a,  the  equivalent  contents  are  then 
compared to the constants TCi, which have been experimentally found using nitrogen as the (only) 
inert gas. 

It should be noted that ISO 10156 uses molar fractions in some of its equations. For most gases 
under normal (i.e. non-extreme) conditions the volume fraction can be assumed to be equal to 
the molar fraction, which is the same as assuming ideal gas behaviour for all gases in the mixture. 
Furthermore, although normally a fraction is a number ranging from 0 to 1, in this case it is easier 
to express it as percentage, i.e. the fraction multiplied by 100. 

The calculation methods described in ISO 10156 allows the determination of a lower explosion 
limit and therefore the calculation method can determine whether the mixture is classified as a 
flammable gas in category 1A or category 1B. 

For mixtures of flammable gases, the Le Chatelier's formula is commonly used to predict lower 
explosion limits. The formula can be applied to flammable mixtures but not to potentially explosive 
mixtures.  Le  Chatelier's  formula  cannot  be  used  for  calculation  of  upper  explosion  limits. 
Furthermore, it cannot be used for partially halogenated hydrocarbons or oxidisers other than air. 

According to this formula, the lower  flammability limit  (LM) of a mixture  of flammable gases is 
given by the following equation: 

Equation 2.2.4.4.c 

100
𝐿𝑀

=

𝐴1

𝐿1

+

𝐴2

𝐿2

+

𝐴3

𝐿3

+ ⋯ +

𝐴𝑛

𝐿𝑛

Where L is the lower flammability limit in % and A is the molar fraction in % of the flammable 
gas in a mixture of n flammable gases. 

For mixtures of flammable gases with inert gases other than nitrogen and air, Equation 2.2.4.4.d 
takes into account the nitrogen equivalent (Kk) of inert gases other than nitrogen. 

Equation 2.2.4.4.d 

𝐿𝑀 =

where 𝐿𝑖

´  is given by  

Equation 2.2.4.4.e 

´ =  
𝐿𝑖

where:  

100
𝑛
𝑖=1

∑

𝐴 𝑖
𝐿´𝑖

(100− 𝐿𝑀

´ − (1−𝐾)∗ 

∑

𝑝
𝑘=1
𝑛
∑
𝑖=1
´ )
(100−𝐿𝑀

𝐵𝑘
𝐴𝑖

´ )
∗ 𝐿𝑀

∗   𝐿𝑖 

ciTiAkBkKnpiA' 
 
 
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K is the average of Kk values of the inert gases weighted according to their molar 
fractions. 

The calculation method described in ISO 10156 does not determine a flammability range so the 
calculation  method  cannot  determine  whether  the  mixture  is  flammable  in  category  1A/1B  or 
category 2. Therefore, to be on the safe side, mixtures determined to be flammable according to 
the calculation method are classified as flammable gas in category 1A or 1B. The gas mixture can 
be  classified  as  flammable  gas  category  2  only  if  it  contains  flammable  gases  classified  as 
flammable  gas  category  2.  In  these  cases,  the  lower  and  the  upper  explosion  limits  can  be 
determined by using a suitable test method (e.g. EN 1839:201731 or ISO 10156). 

For mixtures containing both flammable and oxidising components, special calculation methods 
are described in ISO 10156. 

In case a gas or gas mixture needs to be tested for its flammability, a recognised international 
standard must be used; CLP explicitly refers to ISO 10156. Instead of the test apparatus according 
to  ISO  10156,  the  test  apparatus  for  the  tube  method  according  to  clause  4.2  of  EN  1839, 
‘Determination of the explosion limits and the limiting oxygen concentration (LOC) for flammable 
gases and vapour’ may be used. 

Gases  (including  gas  mixtures)  that  are  classified  as  flammable  have  to  be  considered  for 
classification as  pyrophoric and/or  chemically  unstable in addition. If  the screening procedures 
described in section 2.2.4.2 are not conclusive, the gas or gas mixture has to be tested.  

Gases do not have to be tested for pyrophoricity for classification purposes (see above in 2.2.4.2) 
but if tested, the test must be carried out at 54 °C in accordance with either ISO/IEC 80079-20-
1:2017  ‘Explosive  atmospheres  –  Part  20-1:  Material  characteristics  for  gas  and  vapour 
classification – Test methods and data’ or DIN32 51794 ‘Determining the ignition temperature of 
petroleum products’. 

The test method for chemical instability of gases is described in UN-MTC, section 35. It uses the 
same equipment as the test method for oxidising gases according to ISO 10156 and so could be 
applied by laboratories that also carry out the tests for oxidising gases. 

If information on other gases or gas mixtures than the ones mentioned in the tables referred to 
in the last paragraph of 2.2.4.2 is needed, testing should be performed. It should be noted that 
the  test  method  described  in  UN-MTC,  section  35,  does  not  cover  gas  mixtures  where  the 
components can react dangerously with each other, e.g. flammable and oxidising gases. It is not 
applicable  to  liquefied  gas  mixtures  because  the  gaseous  phase  above  a  liquefied  gas  mixture 
may  generally  have  a  different  composition  than  the  liquefied  phase  (except  if  the  mixture  is 
azeotropic and at its azeotropic point), so that the gas may become chemically unstable only after 
withdrawal. This should be communicated via the SDS. 

2.2.4.5. 

Decision logics 

Classification of flammable gases is laid down in the following flow-charts which are applicable 
according to CLP. 

  NOTE: The person responsible for the classification of flammable gases  should be 

experienced in this field and be familiar with the criteria for classification.  

Decision logic for flammable gases  

31 Hereafter: EN 1839 

32 DIN: Deutsches Institut für Normung 

 
 
 
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Annex I: Figure 2.2.1 

Flammable gases 

 
 
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2.2.5.  Hazard communication for flammable gases  

2.2.5.1. 

Pictograms, signal words, hazard statements and precautionary statements 

Annex I: 2.2.3. Table 2.2.2  Label elements for flammable gases 

Category 1A 

Gases categorised as 1A meeting pyrophoric or unstable gas A/B criteria 

Category 1B 

Category 2 

Pyrophoric gas 

Chemically unstable gas 

Category A 

Category B 

GHS Pictogram 

No pictogram 

Signal Word 

Danger 

Danger 

Danger 

Danger 

Danger 

Warning 

Hazard Statement 

H220: Extremely 
flammable gas 

H220: Extremely 
flammable gas 

H232: May ignite 
spontaneously if 
exposed to air 

H220: Extremely 
flammable gas  

H230: May react 
explosively even in the 
absence of air 

H220: Extremely 
flammable gas 

H231: May react 
explosively even in the 
absence of air at elevated 
pressure and/or 
temperature 

H221: Flammable gas 

H221: Flammable gas 

Precautionary Statement 
Prevention 

Precautionary Statement 
Response 

P210 

P377 

P381 

P210 

P222 

P280 

P377 

P381 

P202 

P210 

P377 

P381 

P202 

P210 

P377 

P381 

P210 

P210 

P377 

P381 

P377 

P381 

 
 
 
 
 
 
 
 
 
 
 
 
 
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Precautionary Statement 
Storage 

Precautionary Statement 
Disposal 

P403 

P403 

P403 

P403 

P403 

P403 

 
 
 
 
 
 
 
 
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Annex I: 2.2.3 

Hazard Communication 

[…] 

If a flammable gas or gas mixture is classified as pyrophoric and/or chemically unstable, 
then all relevant classification(s) shall be communicated on the safety data sheet as 
specified in Annex II of Regulation (EC) No 1907/2006, and the relevant hazard 
communication elements included on the label. 

[…] 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.2.6.  Relation to transport classification 

The  criteria  for  flammable  gases  categories  1A  and  1B  do  not  completely  correspond  to  the 
criteria  that  are  in  use  for  classifying  flammable  gases  in  the  UN  RTDG  Model  Regulations. 
Consequently, all gases listed as flammable in the UN RTDG Model Regulations and in the modal 
transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) must be classified as Flam. Gas 
1A (H220) or 1B (H221). Gases are not classified for chemical instability or for pyrophoricity in 
the  UN  RTDG  Model  Regulations.  See  Annex  I  for  additional  information  on  transport 
classification in relation to CLP classification. 

2.2.7.  Example of classification for flammable gases 

EXAMPLE MIXTURE:  2 % (H2) + 6 % (CH4) + 27 % (Ar) + 65 % (He) 

Calculation steps: 

Example for the classification of a gas mixture containing flammable gases based on the 
calculations of ISO 10156. 

Step 1: Assign the gases and state their molar fractions, assuming the molar fractions are 
equal to the volume fractions (ideal gas behaviour for all gases). 

H2 is flammable gas 1, 
Press. Gas (Comp), H280; 
Flam. Gas 1A, H220 

CH4 is flammable gas 2, 
Press. Gas (Comp), H280; 
Flam. Gas 1A, H220 

Ar is inert gas 1,         
Press. Gas (Comp), H280; 

He is inert gas 2,        
Press. Gas (Comp), H280 

yielding  = 2 mole % 

yielding  = 6 mole % 

yielding  = 27 mole % 

yielding  = 65 mole % 

=2  

=2  

since there are two flammable gases in the mixture 

since there are two inert gases in the mixture 

Step 2: Assessment of pyrophoricity and chemical instability 

As no substance of the mixture is either pyrophoric or chemically unstable the mixture is not pyrophoric 
and not chemical unstable. 

Step 3: Look up the values of 

, 

 and Li in ISO 10156. 

1A2A1B2BnpciTkK 
 
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= 

= 

Li1 = 

Li2 = 

=  

= 

5.5 mole % 

8.7 mole % 

4.0 mole % 

4.4 mole % 

0.55 

0.9 

Step 4: Calculate the equivalent gas contents

 for the flammable gases according to 

Equation 2.2.3.3.b 

= 2.46 mole % 

 = 7.38 mole % 

Step 5: Calculate the flammability of the gas mixture according to Equation 2.2.4.4.a 

= 1.29 

Step 6: Compare the outcome to the criterion in Equation 2.2.4.4.a 

Since 1.29 > 1, this particular gas mixture is considered to be flammable. 

EXAMPLE MIXTURE:  2 % (H2) + 6 % (CH4) + 27 % (Ar) + 65 % (He) 

Step 7: Calculate the lower explosion limit LM according to Equations 2.2.4.4.c, 2.2.4.4.d and 
2.2.2.4.e 

𝐿𝑀 =

100

25
4

+  

75
4.4

= 4.29 𝑚𝑜𝑙𝑒 % 

𝐾 =  

27 ∗ 0.55 + 65 ∗ 0.9
(27 + 65)

= 0.797 

´ =  
𝐿𝐻2

(100 −  4.29 −   (1 − 0.797) ∗  

27 + 65
2 + 6

∗  4.29)

(100 − 4.29)

∗  4 = 3.58 𝑚𝑜𝑙𝑒 % 

´
𝐿𝐶𝐻4

=  

(100 −  4.29 −   (1 − 0.797) ∗  

27 + 65
2 + 6

∗  4.29)

(100 − 4.29)

∗  4.4 = 3.94 𝑚𝑜𝑙𝑒 % 

1cT2cT1K2KiA'()()659.02755.0622'1+++=A()()659.02755.0626'2+++=A7.838.75.546.2'''221121+=+==cciciiTATATA 
 
 
 
 
 
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𝐿𝑀 =

100

2
3.58

+  

6
3.94

= 48.04 𝑚𝑜𝑙𝑒 % 

Step 8: Compare the outcome to the criterion in CLP 

As the upper explosion limit cannot be calculated, it is not known if this mixture has a 
flammable range with air of at least 12 percentage points regardless of the lower flammable 
limit. 

Since LM is > 6%, this particular gas mixture is classified as a flammable gas category 1B, 
H221. 

In addition, it is classified as gas under pressure, H280. 

2.2.8.  References 

Le Chatelier, H. L., Note sur le dosage du grisou par les limetes de l‘inflammabilité, Annales 
des mines 19 (1891) 388–395 

2.3.  AEROSOLS 

2.3.1.  Introduction 

As of GHS revision 8, chapter 2.3 regarding aerosols has been split into two sub-chapters – one 
for aerosols and the other for chemicals under pressure. The latter is a new hazard class from 
GHS  revision  8  and  onwards,  which  is  not  yet  implemented  in  the  current  version  of  the  CLP 
Regulation18. Other than a renumbering of the paragraphs there was no change for the class of 
aerosols. 

The European Aerosol Dispenser Directive 75/324/EEG (ADD), as regards the flammability and 
pressure hazards, is fully aligned with the classification (and labelling) of aerosols under CLP. 

2.3.2.  Definitions and general considerations for classification of aerosols 

Annex I: 2.3.1. 

Definitions 

Aerosols, this means aerosol dispensers, are any non-refillable receptacles made of metal, 
glass or plastics and containing a gas compressed, liquefied or dissolved under pressure, 
with or without a liquid, paste or powder, and fitted with a release device allowing the 
contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or 
powder or in a liquid state or in a gaseous state. 

It should be noted that the type  of  aerosol  container may affect the  outcome of  flammability 
tests for aerosols which may, in turn, affect the classification if it is based on testing. 

2.3.3.  Relation to other physical hazards 

As  the  class  of  aerosols  includes  the  flammability  aspects,  they  should  not  be  classified  as 
flammables  gases,  flammable  liquids  or  flammable  solids  in  addition.  However,  other 
classifications may apply to aerosols (as for any other container). 

 
 
 
 
 
 
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Annex I, 2.3.2.1. 

[…] 

NOTE 2: Aerosols do not fall additionally within the scope of Sections 2.2 (flammable gases), 2.5 (gases under 
pressure), 2.6 (flammable liquids) and 2.7 (flammable solids). Depending on their contents, aerosols may however 
fall within the scope of other hazard classes, including their labelling elements. 

2.3.4.  Classification of aerosols 

2.3.4.1. 

Classification criteria 

Annex I: 

2.3.2.1. Aerosols shall be classified in one of the three categories of this hazard class, 
depending on their flammable properties and their heat of combustion. They shall be 
considered for classification in Category 1 or 2 if they contain more than 1% components (by 
mass) which are classified as flammable according to the following criteria set out in this Part: 

– Flammable gases (see Section 2.2); 

– Liquids with a flash point ≤ 93 °C, which includes Flammable Liquids according to section 
2.6; 

– Flammable solids (see Section 2.7); 

or if their heat of combustion is at least 20kJ/g. 

NOTE 1: Flammable components do not cover pyrophoric, self-heating or water-reactive 
substances and mixtures because such components are never used as aerosol contents. 

[…] 

2.3.2.2. An aerosol shall be classified in one of the three categories for this Class on the basis 
of its components, of its chemical heat of combustion and, if applicable, of the results of the 
foam test (for foam aerosols) and of the ignition distance test and enclosed space test (for 
spray aerosols) in accordance with Figures 2.3.1(a) to 2.3.1(c) of this Annex and sub-sections 
31.4, 31.5 and 31.6 of Part III of the UN RTDG, Manual of Tests and Criteria. Aerosols which 
do not meet the criteria for inclusion in Category 1 or Category 2 shall be classified in 
Category 3. 

Note: Aerosols containing more than 1% flammable components or with a heat of combustion 
of at least 20 kJ/g, which are not submitted to the flammability classification procedures in 
this section shall be classified as aerosols, Category 1. 

Under  the  ADD  and  in  UN-MTC,  section  31,  flammability  classification  for  aerosols  refers  to 
‘extremely flammable’, ‘flammable’ and ‘not classified as flammable aerosol’. This  respectively 
corresponds to the terms ‘Aerosol, category 1’, ‘Aerosol, category 2’ and ‘Aerosol, category 3’ 
which are used in CLP. 

In CLP, the full set of criteria including those based on testing are included only by reference 
(see CLP Annex I, section 2.3.2.2) and in the decision logic. GHS revision 7 contains the 
following criteria table with the full set of criteria: 

 
 
 
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Table 2.1 Criteria for aerosols (Table 2.3.1 of the GHS) 

Category  Criteria 

1 

2 

3 

(a)   Any aerosol that contains ≥ 85 % flammable components (by mass) and 

has a heat of combustion of ≥ 30 kJ/g;  

(b)  Any aerosol that dispenses a spray that, in the ignition distance test, has 

an ignition distance of ≥ 75 cm; or 

(c)   Any aerosol that dispenses a foam that, in the foam flammability test, has: 

(i)   a flame height of ≥ 20 cm and a flame duration of ≥ 2 s; or 

(ii)   a flame height of ≥ 4 cm and a flame duration of ≥ 7 s. 

(a)  Any aerosol that dispenses a spray that, based on the results of the ignition 
distance test, does not meet the criteria for Category 1, and which has: 

(i)   a heat of combustion of ≥ 20 kJ/g;  

(ii)   a heat of combustion of < 20 kJ/g along  with  an ignition distance  of 

≥ 15 cm; or 

(iii)  a heat of combustion of < 20 kJ/g and an ignition distance of < 15 cm 

along with either, in the enclosed space ignition test: 

-  a time equivalent of ≤ 300 s/m3; or 

-  a deflagration density of ≤ 300 g/m3; or 

(b)  Any aerosol that dispenses a foam that, based on the results of the aerosol 
foam flammability test, does not meet the criteria for Category 1, and which 
has a flame height of ≥ 4 cm and a flame duration of ≥ 2 s. 

(a)  Any aerosol that contains ≤ 1 % flammable components (by mass) and that 

has a heat of combustion < 20 kJ/g; or 

(b)  Any aerosol that contains > 1 % (by mass) flammable components or which 
has a heat of combustion of ≥ 20 kJ/g but which, based on the results of 
the  ignition  distance  test,  the  enclosed  space  ignition  test  or  the  aerosol 
foam  flammability  test,  does  not  meet  the  criteria  for  Category  1  or 
Category 2. 

NOTE 1: 
substances and mixtures because such components are never used as aerosol contents. 

Flammable  components  do  not  cover  pyrophoric,  self-heating  or  water-reactive 

NOTE 2: 
Aerosols  containing  more  than  1 %  flammable  components  or  with  a  heat  of 
combustion  of  at  least  20 kJ/g,  which  are  not  submitted  to  the  flammability  classification 
procedures in this chapter should be classified as aerosols, Category 1. 

Aerosols do not fall additionally within the scope of chapter 2.2 (flammable gases), 
NOTE 3: 
section 2.3.2 (chemicals under pressure), chapters 2.5 (gases under pressure), 2.6 (flammable 
liquids)  and  2.7  (flammable  solids).  Depending  on  their  contents,  aerosols  may  however  fall 
within the scope of other hazard classes, including their labelling elements. 

The chemical heat of combustion is determined in accordance with CLP Annex I, section 2.3.4.1 
which is identical to point 1.10 of the Annex to ADD. 

2.3.4.2. 

Testing and evaluation of hazard information 

Results from the ignition distance test, the enclosed space test, and the foam flammability test 
may be used for classification related to the flammability of aerosols. The enclosed space test 

 
 
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should be performed only for spray aerosols and, if no ignition was observed, during the ignition 
distance  test.  Performing  the  enclosed  space  test  erroneously  may  lead  to  safety  issues.  The 
test  methods  referred  to  above  are  described  under  point  6.3  of  the  Annex  to  ADD  and  are 
therefore available in all EU languages. They are also described in the UN-MTC section 31. 

After  evaluation  according  to  the  appropriate  criteria  (see  previous  sections)  the  aerosol  is 
classified in one of the three categories. 

2.3.4.3. 

Decision logics 

The classification procedure is also laid down in the following flow-charts which are applicable 
according to CLP.  

  NOTE: The person responsible for the classification of aerosols should be experienced in this 

field and be familiar with the criteria for classification. 

 
 
 
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2.3.4.3.1.  Decision logics for aerosols 

Annex I: Figure 2.3.1 (a) 

for aerosols 

AEROSOL 

Category 3 

No pictogram 

Warning 

Category 1 

Danger 

Does it contain ≤ 1% flammable 
components (by mass) and does it 
have a heat of combustion < 20 kJ/g? 

Does it contain ≥ 85% flammable 
components (by mass) and does it 
have a heat of combustion ≥ 30 kJ/g? 

For spray aerosols, go to decision 
logic 2.3.1 (b) 

For foam aerosols, go to decision logic 
2.3.1 (c) 

   YES  NO  YES  NO  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.3.4.3.2.  Decision logics for spray aerosols 

Annex I: Figure 2.3.1 (b)  Spray aerosols 

SPRAY AEROSOL 

In the ignition distance test, does ignition occur 
at a distance ≥ 75 cm? 

YES 

NO 

Does it have a heat of combustion < 20 kJ/g? 

NO 

YES 

In the ignition distance test, does ignition occur 
at a distance ≥ 15 cm? 

NO 

In the enclosed space ignition test; is: 

(a) the time equivalent ≤ 300 s/m³ or 

(b) the deflagration density ≤ 300 g/m³? 

YES 

YES 

NO 

Category 3 

No pictogram 

Warning 

Category 1 

Danger 

Category 2 

Warning 

Category 2 

Warning 

Category 2 

Warning 

 
 
 
 
 
 
 
 
 
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2.3.4.3.3.  Decision logics for foam aerosols 

Annex I: Figure 2.3.1 (c)  Foam aerosols 

FOAM AEROSOL 

In the foam test, is: 

(a) the flame height ≥ 20 cm and the flame duration ≥ 2 s; or 
(b) the flame height ≥ 4 cm and the flame duration ≥ 7 s? 

YES 

NO 

In the foam test; is the flame height ≥ 4 cm and the flame 
duration ≥ 2 s? 

YES 

Category 1 

Danger 

Category 2 

Warning 

NO 

Category 3 

No pictogram 

Warning 

2.3.5.  Hazard communication for aerosols 

2.3.5.1. 
statements 

Pictograms, signal words, hazard statements and precautionary 

Annex I: Table 2.3.1 

Label elements for aerosols 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

No pictogram 

Signal Word 

Danger 

Warning 

Warning 

Hazard Statement 

H222: Extremely 
flammable aerosol 

H223: Flammable 
aerosol 

H229: Pressurised 
container: May burst 
if heated. 

H229: Pressurised 
container: May burst 
if heated. 

H229: Pressurised 
container: May burst 
if heated. 

 
 
 
 
 
 
 
 
 
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P210 

P211 

P251 

P210 

P211 

P251 

P210 

P251 

P410 + P412 

P410 + P412 

P410 + P412 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement Response 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.3.5.2. 

Additional labelling provisions 

The ADD imposes additional labelling requirements on aerosols. 

2.3.6.  Relation to transport classification 

Aerosol dispensers (UN 1950) belong to Class 2 in the UN RTDG Model Regulations and in the 
modal  transport  regulations  (ADR,  RID,  ADN  and  IMDG  Code,  ICAO  TI).  Flammability 
classification  criteria are harmonised between  CLP and the  modal transport regulations (ADR, 
RID, ADN and IMDG Code, ICAO TI). 

Aerosols, categories 1 and 2 fall under Division 2.1 (sometimes referred to as Class 2.1 or Group 
F, FC, TF or TFC depending on their contents with hazardous properties). Aerosols, category 3 
fall under Division 2.2 (sometimes referred to as Class 2.2 or Group A, O, T, C, CO, TC or TOC 
depending on their contents with hazardous properties). See Annex I for additional information 
on transport classification in relation to CLP classification. 

2.3.7.  Example of classification for aerosols 

For reasons of simplification, the active materials chosen in the examples have been considered 
as non-combustible materials (Hc = 0 kJ/g). However, this may not be the case in practice. 

2.3.7.1. 
criteria 

Example of substances and mixtures fulfilling the classification 

Deodorant: 

Composition: 

         Butane/propane:  

70 % (flammable components, Hc = 43.5 kJ/g) 

         Ethanol:   

25 % (flammable components, Hc = 24.7 kJ/g) 

         Others:   

5 % (non-flammable components, Hc = 0 kJ/g) 

This spray aerosol contains 95 % of flammable components, and its chemical heat of combustion 
equals 36.6 kJ/g (= 0.70 * 43.5 + 0.25 * 24.7). 

This aerosol is classified as Aerosol, category 1. 

 
 
 
 
 
 
 
 
 
 
 
 
 
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Air freshener (wet): 

Composition: 

         Butane/propane: 

30 % (flammable components, Hc = 43.5 kJ/g) 

         Others:   

70 % (non-flammable components, Hc = 0 kJ/g) 

This spray aerosol contains 30 % of flammable components and its chemical heat of combustion 
equals 13.1 kJ/g. 

In the ignition distance test, the ignition occurs at less than 75 cm but more than 15 cm. 

This aerosol is classified as Aerosol, category 2. 

Shaving foam: 

Composition: 

         Butane/propane:  

4 % (flammable components, Hc = 43.5 kJ/g) 

         Others:   

96 % (non-flammable components, Hc = 0 kJ/g) 

This foam aerosol contains 4 % of flammable components and its chemical heat of combustion 
equals 1.7 kJ/g. 

In the foam test, the flame height is less than 4 cm and the flame duration less than 2 s. 

This aerosol is classified as Aerosol, category 3. 

2.3.7.2. 

Examples of aerosols not fulfilling the classification criteria  

By definition, all aerosol dispensers fall under one of the three categories for this hazard class. 

2.4.  OXIDISING GASES 

2.4.1.  Introduction 

The  requirements  in  chapter  2.4  ‘Oxidising  gases’  of  Annex  I  to  CLP  are  identical  to  those  in 
chapter 2.4 of GHS18. 

2.4.2.  Definitions and general considerations for the classification of 

oxidising gases 

Annex I: 2.4.1. Oxidising gas means any gas or gas mixture which may, generally by 
providing oxygen, cause or contribute to the combustion of other material more than air 
does. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.4.3.  Relation to other physical hazards 

Oxidising gases usually do not need to be classified in any other physical hazard class apart 
from ‘Gases under pressure’, ‘Chemicals under pressure’ or ‘Aerosol’ where appropriate. 

2.4.4.  Classification of substances and mixtures as oxidising gases 

2.4.4.1. 

Identification of hazard information 

There are not many pure gases that are oxidising. Most oxidising gases are identified as such in 
the UN RTDG Model Regulations and in ISO 10156. 

If  no  or  insufficient  information  is  available,  screening  and  waiving  possibilities  should  be 
checked. Depending on the results testing might be necessary, see section 2.4.4.2. 

2.4.4.2. 

Screening procedures and waiving of testing 

Gas mixtures are often prepared on demand, so there are thousands of gas mixtures containing 
oxidising gases on the market. However, there are very few test reports or data on the oxidising 
potential of gas mixtures in the scientific literature. Tests according to ISO 10156 to determine 
the oxidising potential are time consuming and expensive. In most cases, a calculation method 
as described in ISO 10156 may be applied. 

2.4.4.3. 

Classification criteria 

Annex I: 2.4.2. Table 2.4.1 

Criteria for oxidising gases 

Category  Criteria 

Any gas which may, generally by providing oxygen, cause or contribute to the 
combustion of other material more than air does. 

1 

Note: 

‘Gases which cause or contribute to the combustion of other material more than air does’ 
means pure gases or gas mixtures with an oxidising power greater than 23.5 % as 
determined by a method specified in ISO 10156 as amended. 

2.4.4.4. 

Testing and evaluation of hazard information 

ISO 10156 describes a test method and a calculation method for the classification of oxidising 
gases. The test method may be used in all cases but must be used when the calculation method 
cannot be applied. 

The  calculation  method  applies  to  gas  mixtures  and  can  be  applied  only  when  the  Ci  for  all 
oxidising components and the Kk for all inert components are available. These are listed for a 
number of gases in ISO 10156. For gas mixtures the calculation method described in ISO 10156 
uses  the  criterion  that  a  gas  mixture  should  be  considered  as  more  oxidising  than  air  if  the 
‘Oxidising Power’ (OP) of the gas mixture is higher than 0.235 (23.5 %). 

The OP is calculated as follows: 

Equation 2.4.4.4.a 

Where: 

===+=nipkkkiniiiBKxCxOP111 
 
 
 
 
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Ci 

Kk 

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is the molar fraction of the i:th oxidising gas in the mixture, in % 

is the coefficient of oxygen equivalency of the i:th oxidising gas in the mixture 

is the coefficient of equivalency of the k:th inert gas relative to nitrogen 

is the molar fraction of the k:th inert gas in the mixture, in % 

is the number of oxidising gases in the mixture 

is the number of inert gases in the mixture. 

For mixtures containing both flammable and oxidising components, special calculation methods 
are described in ISO 10156. 

In  case  a  gas  or  gas  mixture  needs  to  be  tested  for  its  oxidising  potential,  a  recognised 
international standard must be used, notes that CLP explicitly refers to ISO 10156. 

2.4.4.5. 

Decision logic  

Classification of oxidising gases is done according to decision logic 2.4 in section 2.4.4.1 of 
GHS. 

  NOTE: The person responsible for the classification of oxidising gases should be experienced 

in this field and be familiar with the criteria for classification. 

Figure 2.1 Decision logic for oxidising gases (Decision logic 2.4 of GHS) 

Gaseous substance or mixture of gases 

Does the gas contribute to the combustion of 
other material more than air does? 

YES 

NO 

Not classified 

Category 1 

Danger 

2.4.5.  Hazard communication for oxidising gases 

2.4.5.1. 
statements  

Pictograms, signal words, hazard statements and precautionary 

Annex I: Table 2.4.2 

Label elements for oxidising gases 

Classification 

Category 1 

GHS Pictogram 

Signal word 

Danger 

Hazard statement 

H270: May cause or intensify fire; oxidiser 

np 
 
 
 
 
 
 
 
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Precautionary Statement Prevention 

P220 

P244 

Precautionary Statement Response 

P370 + P376 

Precautionary Statement Storage 

P403 

Precautionary Statement Disposal 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.4.6.  Relation to transport classification 

Most  oxidising  gases  are  classified  as  gases  with  subsidiary  risk  5.1  in  the  UN  RTDG  Model 
Regulations. Consequently, all gases listed as oxidising in the UN RTDG Model Regulations and 
in the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) must be classified 
as Ox. Gas 1. See Annex I for additional information on transport classification in relation to CLP 
classification. 

2.4.7.  Example of classification for oxidising gases   

2.4.7.1. 
classification criteria  

Example of substances and mixtures not fulfilling the 

EXAMPLE OF A CLASSIFICATION USING THE CALCULATION METHOD OF ISO 10156  

Example Mixture: 9 % (O2) + 16 % (N2O) + 75 % (N2) 

Calculation steps 

Step 1: Ascertain the coefficient of oxygen equivalency (Ci) for the oxidising gases in the mixture and 
the nitrogen equivalency factors (Kk) for the non-flammable, non-oxidising gases. 

Ci (N2O) =  

0.6 (nitrous oxide) 

Ci (O) = 

1 (oxygen) 

Kk (N2) = 

1 (nitrogen) 

Step 2: Calculate the Oxidising Power (OP) of the gas mixture according to Equation 2.4.4.4.a 

0.186 < 0.235 (18.6 % < 23.5 %), therefore the mixture is not considered as an 
oxidising gas. 

186.0175.016.009.06.016.0109.0111=+++=+====nipkkkiniiiBKxCxOP 
 
 
 
 
 
 
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EXAMPLE OF A CLASSIFICATION USING THE CALCULATION METHOD OF ISO 10156  

Example Mixture: 9 % (O2) + 16 % (N2O) + 75 % (Ar) 

Calculation steps 

Step 1: Ascertain the coefficient of oxygen equivalency (Ci) for the oxidising gases in the mixture and 
the nitrogen equivalency factors (Kk) for the non-flammable, non-oxidising gases. 

Ci (N2O) =  

0.6 (nitrous oxide) 

Ci (O) = 

1 (oxygen) 

Kk (Ar) = 

0.55 (argon) 

Step 2: Calculate the Oxidising Power (OP) of the gas mixture according to Equation 2.4.4.4.a 

𝑂𝑃 =

𝑛
∑ 𝑥𝑖𝐶𝑖
𝑖=1
𝑝
∑ 𝑥𝑖 + ∑
𝑘=1

𝑛
𝑖=1

𝐾𝑘𝐵𝑘

=

0.09 × 1 + 0.16 × 0.6
0.09 + 0.16 + 0.75 × 0.55

= 0.281 

0.281 > 0.235 (28.1 % > 23.5 %), therefore the mixture is considered as an 
oxidising gas. 

2.5.  GASES UNDER PRESSURE 

2.5.1.  Introduction 

The requirements in chapter 2.5 ‘Gases under pressure’ of Annex I to CLP are identical to those 
in chapter 2.5 of GHS18. The hazard class ‘Gases under pressure’ corresponds to Class 2 ‘Gases’ 
in the UN RTDG Model Regulations.   

2.5.2.  Definitions and general considerations for classification of gases 

under pressure 

2.5.2.1. 

Definition of ‘gas’ 

Annex I: 1.0. Gas means a substance which (i) at 50 °C has a vapour pressure greater 
than 300 kPa (absolute); or (ii) is completely gaseous at 20 °C at a standard pressure of 
101.3 kPa; 

This definition means that substances and mixtures are considered as gases when their boiling 
point or initial boiling point (BP) is not higher than 20 °C. Substances and mixtures with a 
boiling point or initial boiling point higher than 20 °C are liquids except those few that develop 
a vapour pressure higher than 300 kPa at 50 °C; these substances and mixtures are 
considered as gases because of the pressure hazard when packaged. 

Hydrogen fluoride (HF) with a BP of 19.4 °C is a borderline line case that has always been 
classified as a liquid. 

 
 
 
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2.5.2.2. 

Definition of gases under pressure 

Annex I: 

2.5.1.1. Gases under pressure are gases which are contained in a receptacle at a pressure 
of 200 kPa (gauge) or more at 20 °C, or which are liquefied or liquefied and refrigerated. 

They comprise compressed gases, liquefied gases, dissolved gases and refrigerated liquefied 
gases. 

2.5.1.2. The critical temperature is the temperature above which a pure gas cannot be 
liquefied, regardless of the degree of compression. 

This definition means in practice that compressed gases or dissolved gases that are packaged at 
a pressure less than 200 kPa are not classified for this hazard. 

Dissolved gases packaged at a pressure less than 200 kPa  (gauge)  are liquids and  should be 
classified as such if they have other hazardous properties, e.g. flammable liquids. 

Furthermore, liquids packaged under a layer of inert gas (e.g. nitrogen or helium) remain to be 
classified as liquids and not as gases under pressure. 

2.5.3.  Relation to other physical hazards 

Gases under pressure may also need to be classified as flammable gases and oxidising gases 
where relevant. 

2.5.4.  Classification of substances and mixtures as gases under pressure 

2.5.4.1. 

Identification of hazard information 

Many gases are identified as such in the UN RTDG Model Regulations and many flammable gases 
and some oxidising gases are identified as gases in Annex VI of CLP. Furthermore, the UN RTDG 
Model Regulations specifies whether the gas can be packaged as a ‘compressed gas’, a ‘liquefied 
gas’, a ‘refrigerated liquefied gas’ and a ‘dissolved gas’. To determine whether a substance is a 
gas in case it is not listed in the UN RTDG Model Regulations and in case of doubt, the following 
physical characteristics are necessary: 

• 

• 

the boiling point; 

the vapour pressure at 50 °C. 

See also IR  & CSA, Chapter R.7a: Endpoint specific guidance,  sections R.7.1.3 (Boiling point) 
and R.7.1.5 (Vapour pressure). 

For  those  substances  that  meet  the  definition  of  a  gas  (see  section  2.5.2),  the  critical 
temperature is also necessary. For the classification of gas mixtures based on the pseudo-critical 
temperature see section 2.5.4.3. 

The  references according to section  2.6.8 provide good quality data  on boiling points, vapour 
pressure and the critical temperature of substances. 

2.5.4.2. 

Classification criteria 

Annex I: Table 2.5.1 

Criteria for gases under pressure 

Group 

Criteria 

Compressed 
gas 

A gas which when packaged under pressure is entirely gaseous at 
- 50 °C; including all gases with a critical temperature  - 50 °C. 

 
 
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A gas which, when packaged under pressure, is partially liquid at 
temperatures above - 50 °C. A distinction is made between: 

Liquefied gas 

high pressure liquefied gas: a gas with a critical temperature 

i) 
between - 50 °C and + 65 °C; and 

low pressure liquefied gas: a gas with a critical temperature above + 

ii) 
65 °C. 

Refrigerated 
liquefied gas 

A gas which when packaged is made partially liquid because of its low 
temperature. 

Dissolved gas 

A gas which when packaged under pressure is dissolved in a liquid phase 
solvent. 

Note:  

Aerosols shall not be classified as gases under pressure. See 2.3. 

NOTE: the distinction between high pressure and low pressure liquefied gas is not relevant 
for classification, only for transport requirements. 

2.5.4.3. 

Testing and evaluation of hazard information 

The critical temperature of pure gases is well defined and can be found in technical literature, 
e.g.  EN  13096  Transportable  gas  cylinders  —  Conditions  for  filling  gases  into  receptacles  — 
Single component gases. 

For gas mixtures, the classification is based on the ‘pseudo-critical temperature’ which can be 
estimated as the mole weighted average of the components’ critical temperatures. 

Pseudo-critical temperature =  

where xi is the molar concentration of component i and T

 is the critical temperature (in °C 

or in K) of the component i.  

2.5.4.4. 

Decision logic 

Classification of gases under pressure is done according to decision logic 2.5.4.1 as included in 
GHS. 

NOTE:  The  person  responsible  for  the  classification  of  gases  under  pressure  should  be 
experienced in this field and be familiar with the criteria for classification. 

=niCritiix1TiCrit 
 
 
 
 
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Figure 2.2 Decision logic for gases under pressure (Decision logic 2.5 of GHS) 

The substance or mixture is a gas 

Is the gas contained in a receptacle at a pressure of 200 kPa 
(gauge) or more at 20°C, or is the gas liquefied or liquefied and 
refrigerated? 

No 

Not classified as a 
gas under 
pressure 

Yes 

Is the gas dissolved in a liquid phase solvent? 

No 

Dissolved gas 

Yes 

Warning 

Refrigerated 
liquefied gas 

Yes 

Is the gas partially liquid because of its low temperature? 

No 

Is the gas partially liquid at temperatures above –50°C? 

No 

Warning 

Yes 

Is its critical temperature above +65°C? 

No 

Is its critical temperature between –50 °C and +65°C? 

Is the gas entirely in gaseous state at –50°C? 

(Low pressure) 
Liquefied gas 

Yes 

Warning 

(High pressure) 
Liquefied gas 

Yes 

Warning 

Compressed gas 

Yes 

Warning 

 
 
 
 
 
 
 
 
 
 
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2.5.5.  Hazard communication for gases under pressure 

2.5.5.1. 
statements 

Pictograms, signal words, hazard statements and precautionary 

Annex I: Table 2.5.2 

Label elements for gases under pressure 

Classification 

Compressed gas 

Liquefied gas 

Refrigerated 
liquefied gas 

Dissolved gas 

GHS Pictogram 

Signal Word 

Warning 

Warning 

Warning 

Warning 

H280: Contains 
gas under 
pressure; may 
explode if heated 

H280: Contains 
gas under 
pressure; may 
explode if heated 

H281: Contains 
refrigerated 
gas; may cause 
cryogenic burns 
or injury 

H280: 
Contains gas 
under 
pressure; 
may explode 
if heated 

P282 

P336 + P315 

P410 + P403 

P410 + P403 

P403 

P410 + P403 

Hazard 
Statement 

Precautionary 
Statements 
Prevention 

Precautionary 
Statements 
Response 

Precautionary 
Statements 
Storage 

Precautionary 
Statements 
Disposal 

Note: Pictogram GHS04 is not required for gases under pressure where pictogram GHS02 or 
pictogram GHS06 appears. 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.5.6.  Relation to transport classification 

Gases are listed in the UN RTDG Model Regulations and in the transport regulations (ADR, RID, 
ADN)33 with an indication of the physical state in their name for compressed gases (e.g. Argon, 
compressed), for refrigerated liquefied gas (e.g. Oxygen, refrigerated liquid) and for dissolved 
gas (e.g. Acetylene, dissolved). These indications of the physical state can be used to identify 
the group of gases under pressure according to CLP. The gas names without an indication of the 
physical state are ‘liquefied gases’ by default. See Annex I for additional information on transport 
classification in relation to CLP classification. 

33 The classification codes according to the ADR, sections 2.2.2.1.2 and 2.2.2.1.3 are: 1. Compressed gas; 2. Liquefied 
gas;  3.  Refrigerated  liquefied  gas;  4.  Dissolved  gas.  An  asphyxiant;  O  oxidizing;  F  flammable;  T  toxic;  TF  toxic, 
flammable; TC toxic, corrosive; TO toxic, oxidizing; TFC toxic, flammable, corrosive; TOC toxic, oxidizing, corrosive. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.5.7.  Example of classification for gases under pressure 

2.5.7.1. 
criteria 

Example of substances and mixtures fulfilling the classification 

2.5.7.1.1. 

Example mixture: 9 % (O2) + 16 % (N2O) + 75 % (N2) 

EXAMPLE MIXTURE: 9 % (O2) + 16 % (N2O) + 75 % (N2) 

Calculation steps: 

Step 1: Ascertain the critical temperatures in Kelvin for the gases in the mixture: 

Oxygen (O2):  

TCrit = -118.4 °C (= 154.75 K) 

Nitrous Oxide (N2O):  

TCrit = +36.4 °C (= 309.55 K) 

Nitrogen (N2):  

TCrit = -147 °C (= 126.15 K) 

Step 2: Calculate the pseudo-critical temperature: 

0.09  154.75 K + 0.16  309.55 K + 0.75  126.15 K= 158.7 Kelvin = - 115.08 °C 

The pseudo-critical temperature is lower than -50 °C, therefore the mixture is a ‘compressed gas’. 

 
 
 
 
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2.6.  FLAMMABLE LIQUIDS 

2.6.1.  Introduction 

The criteria for ‘Flammable liquids’ are found in CLP Annex I, section 2.6. For category 1-3, they 
are identical to those of chapter 2.6 of GHS18. However, CLP has not adopted category 4 of GHS 
(for historical reasons). This means that substances and mixtures classified as flammable liquids 
category 4 according to GHS are not considered flammable liquids according to CLP. 

2.6.2.  Definitions and general considerations for classification of flammable 

liquids 

Annex I: 2.6.1. Flammable liquid means a liquid having a flash point of not more than 60 
°C. 

The  flash  point  is  the  lowest  temperature  of  the  liquid,  corrected  to  a  barometric  pressure  of 
101.3 kPa,  at  which  application  of  a  test  flame  causes  the  vapour  of  the  liquid  to  ignite 
momentarily  and  a  flame  to  propagate  across  the  surface  of  the  liquid  under  the  specified 
conditions of test. This means, the lower explosion limit is exceeded at the flash point. 

2.6.3.  Relation to other physical hazards 

For flammable liquids in aerosol dispensers, see section 2.3 on aerosols. Aerosols should not 
be classified as flammable liquids. 

2.6.4.  Classification of substances and mixtures as flammable liquids 

2.6.4.1. 

Identification of hazard information 

For  the  decision  as  to  whether  a  substance  or  mixture  is  a  liquid  see  section  2.0.4.  For  the 
classification of a substance or mixture as a flammable liquid, data on the flash point and on the 
boiling point (or the initial boiling point) are needed.  

Experimentally  determined  data  or  data  taken  from  reliable  data  sources  are  to  be  preferred 
over calculated ones. The references in section 2.6.8 provide good quality data on boiling points 
(all three references) and flash point (first reference) of substances. 

2.6.4.2. 

Screening procedures and waiving of testing 

2.6.4.2.1. 

Boiling point 

Normally  calculation  methods  based  on  increments  give  satisfying  results  for  substances  and 
mixtures. With respect to the criterion for distinguishing between category 1 and 2 (boiling point 
of 35 °C) only that method with a mean absolute error lower than 5 °C could be recommended 
for screening. 

2.6.4.2.2. 

Flash point 

Calculation should work for pure liquids, neglecting impurities, if the vapour pressure curve and 
lower  explosion  limit  are  accurately  known.  For  mixtures,  calculation  of  the  flash  point  is 
sometimes not reliable, and it is not currently possible to predict the accuracy of a calculated 
value. Calculation can be used as a screening test for mixtures, and a flash point does not need 
to be determined experimentally if the calculated value using the method cited in CLP Annex I, 
section  2.6.4.3  is  5 °C  greater  than  the  relevant  classification  criterion  (23 °C  and  60 °C, 
respectively). However, the restrictions outlined in CLP Annex I, section 2.6.4.2 must be taken 
account of. 

Calculation  based  on  structural  similarity  or  properties  is  often  only  applicable  to  a  narrowly 
defined set of substances. For mixtures they are not yet applicable. 

 
 
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Therefore, for both flash point and boiling point experimental determination is normally required. 

2.6.4.3. 

Classification criteria 

A flammable liquid has to be classified in one of the 3 categories of this class. 

Annex I: Table 2.6.1 

Criteria for flammable liquids 

Category 

Criteria 

1 

2 

3 

Flash point < 23 °C and initial boiling point ≤ 35 °C 

Flash point < 23 °C and initial boiling point > 35 °C 

Flash point ≥ 23 °C and ≤ 60 °C(1) 

(1) For the purpose of this Regulation gas oils, diesel and light heating oils having a flash 

point between > 55 °C and ≤ 75 °C may be regarded as Category 3. 

Note: Aerosols shall not be classified as flammable liquids; see section 2.3. 

Annex I: 2.6.4.5. Liquids with a flash point of more than 35 °C and not more than 60 °C 
need not be classified in Category 3 if negative results have been obtained in the sustained 
combustibility test L.2, Part III, section 32 of the UN RTDG, Manual of Tests and Criteria. 

Gas oils, diesel and light heating oils in the flash point range of 55 °C to 75 °C may be regarded 
as  a  whole.  The  reason  is  that  these  hydrocarbon  mixtures  have  varying  flash  points  in  that 
range due to seasonal requirements (EN 590 Automotive fuels – Diesel- Requirements and Test 
Methods).  If  they  are  regarded  as  a  whole  for  CLP,  they  have  to  be  regarded  as  category 3. 
However,  this  states  no  preliminary  decision  with  respect  to  downstream  regulations  and 
legislation. 

2.6.4.4. 

Testing and evaluation of hazard information 

For experimental determination of the flash point, information on the viscosity of the liquid is 
needed to select a suitable method. Furthermore, to make use of the derogation for classification 
in category 3 according to CLP Annex I,  section 2.6.4.5 (see  section  2.6.4.3), information on 
sustained combustibility is necessary. 

Special care is required when viscous substances or mixtures are tested or when halogenated 
compounds are present (see ‘testing’ below). 

2.6.4.4.1. 

Testing 

Suitable methods are listed in CLP Annex I, Table 2.6.3. 

In  case  of  substances  with  a  high  decomposition  potential,  a  method  using  small  amounts  of 
liquid (e.g. EN ISO 3679 Determination of flash point - Rapid equilibrium closed cup method) is 
recommended to reduce the amount of substance under test. 

The  method  to  be  used  has  to  be  chosen  taking  into  account  the  properties  of  the  liquid 
(viscosity, halogenated compounds present) and the scope of the standard. 

For classification purposes it is recommended to use the mean of at least two test runs. One of 
these  runs  may  be  automated.  In  case  of  a  deviation  between  manual  and  automated 
determination above the tolerance limits of the method, the lower value should be taken, or the 
determination  should  be  repeated  with  manual  observation.  If  the  experimentally  determined 

 
 
 
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flash point is found to be within ± 2 °C a threshold limit when using a non-equilibrium method, 
it is recommended to repeat the determination with an equilibrium method. 

Substances 

For  non-halogenated  substances,  the  flash  point  is  usually  found  80  °C  to  130  °C  below  the 
boiling point. Special care has to be taken when a sample contains impurities with a lower boiling 
point  than  the  main  compound.  Even  if  their  concentration  is  below  0.5 %,  especially  if  their 
boiling point is substantially lower, they may have a strong effect on the test result. Impurities 
with a higher boiling point will normally have no effect on the flash point. 

Within the respective scope, every standard is applicable. However, care must be taken to select 
the appropriate method and standard for the substance being tested. 

Mixtures 

The  flash  point  may  be  lower  than  the  lowest  flash  point  of  the  components  and  non-volatile 
components may influence the flash point. 

Equilibrium methods are advised if the boiling points of the components of the mixture cover a 
wide range of temperatures or if their concentrations are very different. They are also advised 
in case of viscous mixtures (alternatively: test methods with low heating rates (1 °C per min) 
using a stirrer). 

In case of viscous mixtures or if an inerting substance is present at low concentrations and this 
is a highly volatile compound, the ignitability of the mixture may depend on the temperature at 
which  the  tests  are  started.  When  an  inerting  substance  is  present  temperature  ranges  may 
exist where the vapour phase is inerted and other temperature ranges where it is not. 

Halogenated compounds 

The difference between boiling point and flash point may be lower than with non-halogenated 
compounds. 

It is highly recommended to run the tests under careful control with manual observation. 

Test results may be very difficult to reproduce. In such cases, classification should be based on 
the  lowest  value  found  (flash  or  burning  inside  or  outside  the  cup)  or  on  the  value  obtained 
during the screening run if in the main trial performed in accordance with the standard no flash 
could be found. 

2.6.4.4.2. 

Evaluation of hazard information 

Flash points determined by testing or from the mentioned internationally recognised qualified 
literature are to be preferred over those derived by calculation because of the error of most of 
the QSAR34 methods and their limited application range. 

If in literature different flash points are found for the same substance, the one found as evaluated 
or recommended has to be preferred. 

If in literature different flash points are found for the same substance where none is found as 
evaluated/recommended, the lower one has to be preferred because  of  safety  reasons, or an 
experimental determination should be carried out. 

2.6.4.5. 

Decision logic 

Compared to the decision logic 2.6 for flammable liquids contained in GHS chapter 2.6.4.1, this 
decision logic below is amended to exclude category 4 and to include derogations for gas oil, 
diesel, light heating, sustained combustibility and for phrases EUH018, EUH209 and EUH209A. 

34 Quantitative structure–activity relationship 

 
 
 
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NOTE:  The  person  responsible  for  the  classification  of  flammable  liquids  should  be 
experienced in this field and be familiar with the criteria for classification. 

Figure 2.3 Amended GHS decision logic for flammable liquids to include derogations for gas oil, 
diesel, light heating, sustained combustibility and for phrases EUH018, EUH209 and EUH209A 
(see 2.6.5.2 for more information on phrases) 

The substance or mixture is a liquid 

Flash point ≤ 60 °C 

Yes 

No 

Gas oil, diesel, light 
heating oil with flash 
point up to 75 °C 

No 

Yes 

Halogenated 
substance, mixture 
containing 
halogenated, volatile 
or non-volatile 
flammable 
substances 

No 

Yes 

Yes 

No 

Flash point < 23 °C 

No 

Category 3 

Flash point > 35 °C 

No 

Warning 

Yes 

Sustained combustibility 

Yes 

No 

Category 2 

Yes 

Explosive vapour/air 
mixture possible  
(EN 1839, EN 15794) 

No 

Not subject of 
hazard class 
‘flammable liquid’ 

EUH209, 
EUH209A, 
EUH018 

Boiling point ≤ 35 °C 

Yes 

No 

Danger 

No need to be classified as 
‘flammable liquid’ 

Category 1 

Danger 

 
 
 
 
 
 
 
 
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2.6.5.  Hazard communication for flammable liquids 

2.6.5.1. 
statements 

Pictograms, signal words, hazard statements and precautionary 

Annex I: 2.6.3. Table 2.6.2 

Label elements for flammable liquids 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Danger 

Warning 

Hazard 
Statement 

H224: Extremely 
flammable liquid and 
vapour 

H225: Highly 
flammable liquid and 
vapour 

H226: Flammable liquid 
and vapour 

P210 

P233 

P240 

P241 

P242 

P243 

P280 

P210 

P233 

P240 

P241 

P242 

P243 

P280 

P210 

P233 

P240 

P241 

P242 

P243 

P280 

P303 + P361 + P353 

P303 + P361 + P353 

P303 + P361 + P353 

P370 + P378 

P370 + P378 

P370 + P378 

P403 + P235 

P403 + P235 

P403 + P235 

P501 

P501 

P501 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Storage 

Precautionary 
Statement 
Disposal 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.6.5.2. 

Additional labelling provisions for flammable liquids 

If  no  flash  point  is  found  up  to  60  °C  and  (partly)  halogenated  compounds  are  present,  or  if 
there is the possibility of loss of volatile flammable or non-flammable components (i.e. the liquid 
is a candidate for the assignment of EUH018, EUH209 or EUH209A) or if in doubt, the explosion 
limits should be determined to decide whether labelling with EUH018, EUH209, or EUH209A, is 
appropriate. Determination of explosion limits should be carried out according to ISO 10156 or 
EN 15794:200935 Determination of explosion points of flammable liquids or EN 1839. 

35 Hereafter: EN 15794 

 
 
 
 
 
 
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Annex II: 1.1.4. 
mixture' 

EUH018 – 'In use, may form flammable/explosive vapour-air 

For substances and mixtures not classified as flammable themselves, which may form 
flammable/explosive vapour-air mixtures. For substances this might be the case for 
halogenated hydrocarbons and for mixtures this might be the case due to a volatile 
flammable component or due to the loss of a volatile non-flammable component. 

Substances or mixtures which do not show a flash point but do have an explosion range or 
may become flammable in use have to be labelled with EUH018. 

Annex II: 2.9. Liquid mixtures containing halogenated hydrocarbons 

For liquid mixtures which show no flashpoint or a flashpoint higher than 60 ˚C but not more 
than 93 ˚C and contain a halogenated hydrocarbon and more than 5 % highly flammable or 
flammable substances, the label on the packaging shall bear one of the following 
statements, depending on whether the substances referred to above are highly flammable or 
flammable: 

EUH209 — ‘Can become highly flammable in use’ or 

EUH209A — ‘Can become flammable in use’ 

Note:  EUH209  and  EUH209A  are  limited  to  special  types  of  mixtures  whereas  EUH018 
covers a wider  range  of mixtures. In the majority of  cases EUH018  covers EUH209 and 
EUH209A. Information about testing can be found in section 2.6.4.4. 

2.6.6.  Relation to transport classification 

Class 3 of the UN RTDG Model Regulations and the modal transport regulations (ADR, RID, ADN 
and IMDG Code, ICAO TI) cover flammable liquids based on the same criteria as the CLP hazard 
class flammable liquids. In general, there is a correspondence between transport packing groups 
and CLP hazard categories but with exceptions.  

Further, the UN RTDG Model Regulations cover substances and mixtures transported above their 
flash point. In practice the information on flash point and boiling point needed for classification 
is  available  and  it  is  recommended  to  classify  based  on  the  data  rather  than  use  direct 
translation. 

2.6.7.  Example of classification for flammable liquids 

2.6.7.1. 
criteria 

Example of substances and mixtures fulfilling the classification 

2.6.7.1.1. 

Example 1 

MIXTURE OF: N-BUTYLACETATE + P-XYLENE + 1,3,5-TRIMETHYLBENZENE 

(7.9 MOL %     +     60.3 MOL %     +     31.7 MOL %) 

Initial boiling point (calculated): 

Flash point (calculated): 

140 °C 

26 °C 

calculated flash point is within 5 °C to the limiting value of 23 °C 

 flash point has to be measured. 

 
 
 
 
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Dyn. Viscosity at 20 °C (DIN 53019): 

8 mPa·s 

Flash point (EN ISO 3679): 

30.0 °C 

 According to boiling point and measured flash point result: Flam. Liq. category 3 

2.6.7.1.2. 

Example 2 

HYDROCARBONS AND DICHLOROMETHANE (70 VOL %     +     30 VOL %) 

Initial Boiling point (calculated): 

52 °C 

Flash point: 

no flash point according to a standard 

 Because the hydrocarbon part of the mixture has a flash point by itself (- 12 °C) the question ‘Is 
an explosive vapour/air mixture possible?’ (EN 1839, EN 15794) or ‘Can it become highly 
flammable / flammable during use?’ has to be answered. 

Answer: Yes, an explosion range exists; yes, it can become highly flammable during use. 

 According to the answer, the mixture has to be labelled with EUH018 or EUH209 

Note 1: In that case EUH018 covers EUH209 

Note 2: The EUH018 must only be assigned if the substance or mixture is classified as hazardous 
(Article 25 (1) of CLP)  

Cannot be classified as flammable liquid because the mixture has no flash point. 

2.6.7.2. 
classification criteria 

Example of substances and mixtures not fulfilling the 

2.6.7.2.1. 

Example 3 

AQUEOUS FORMULATION OF ALIPHATIC POLYURETHANE RESIN 

Boiling point (EC 440/2008, EU test method A.2): 

92 °C 

Dyn. Viscosity at 20 °C (DIN 53019): 

1938 mPa·s 

Sample is highly viscous, use low heating rate for flash point determination (1 °C /min). 

Flash point (EN ISO 13736): 

42.5 °C 

Sustained combustibility test (UN-MTC L.2) at 60.5 °C: 

combustion not sustained 

Sustained combustibility test (UN-MTC L.2) at 75 °C: 

combustion not sustained 

 According to the flash point result: category 3 

However, does not necessarily have to be classified as flammable liquid category 3 because it did 
not sustain combustion. 

 
 
 
 
 
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2.6.8.  References 

Brandes, E. and Möller, W.: Safety Characteristic Data, Volume 1, Flammable gases and 
liquids, nw-Verlag, 2008 

Haynes W. M. et al. (2012) CRC Handbook of Chemistry and Physics 93rd Edition. CRC Press, 
Taylor and Francis, Boca Raton, FL 

O'Neil, M. J. et al. © (2016, 2012) The Merck Index - An Encyclopedia of Chemicals, Drugs, 
and Biologicals (14th Edition – Version 14.9). Merck Sharp & Dohme Corp., a subsidiary of 
Merck & Co., Inc. 

2.7.  FLAMMABLE SOLIDS 

2.7.1.  Introduction 

The criteria for ‘Flammable solids’ are found in CLP Annex I, section 2.7 and are identical to 
those in chapter 2.7 of GHS18. 

2.7.2.  Definitions and general considerations for classification of flammable 

solids 

Annex I: 2.7.1.1. A flammable solid means a solid which is readily combustible, or may 
cause or contribute to fire through friction. 

Readily combustible solids are powdered, granular, or pasty substances or mixtures which 
are dangerous if they can be easily ignited by brief contact with an ignition source, such as a 
burning match, and if the flame spreads rapidly. 

Special consideration on particle size 

Annex I: 2.7.2.3. 

[…] 

Note 1: The test shall be performed on the substance or mixture in its physical form as 
presented. If for example, for the purposes of supply or transport, the same chemical is to 
be presented in a physical form different from that which was tested and which is considered 
likely to materially alter its performance in a classification test, the substance shall also be 
tested in the new form. 

[…] 

The finer the particle size of a solid substance or mixture, the greater the area exposed to air 
will be, and since flammability is a reaction with the oxygen in air, the particle size will greatly 
influence the ability to ignite. Hence, it is very important that flammable properties for solids are 
investigated  on  the  substance  or  mixture  as  it  is  actually  presented  (including  how  it  can 
reasonably be expected to be used, see Article 8(6) of CLP). This is indicated by the Note cited 
in CLP Annex I, section 2.7.2.3. For further information please see section 1.2 in Part 1. 

2.7.3.  Relation to other physical hazards 

Explosives,  organic  peroxides,  self-reactive  substances  and  mixtures  as  well  as  pyrophoric  or 
oxidising solids should normally not be considered for classification as flammable solids. 

Flammable solids can present other physical hazards, e.g. they might be self-heating or corrosive 
to metals or emit flammable gases in contact with water. 

 
 
 
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For flammable solids that are packaged in aerosol dispensers, see section  2.3. If classified as 
aerosols, they must not be classified as flammable solids in addition. 

2.7.4.  Classification of substances and mixtures as flammable solids 

2.7.4.1. 

Identification of hazard information 

For  the  classification  of  a  substance  or  mixture  as  a  flammable  solid,  data  on  the  following 
properties are needed: 

•  melting point; 

• 

• 

information on water reactivity (due to wetted zone in the test); 

information on flash point for solids containing flammable liquids. 

If a solid with a low melting point is handled in the molten state, additional data such as flash 
point are generally necessary (see Articles 5(1), 6(1) and 8(6)). 

See also IR & CSA, Chapter R.7a: Endpoint specific guidance, sections R.7.1.2 (Melting/freezing 
point) and R.7.1.9 (Flash point). 

Metal  powders  (which  are  powders  of  metals  or  metal  alloys)  may  be  (highly)  flammable 
depending  on  their  reactivity  and  particle  size.  However,  most  other  inorganic  solids  are  not 
flammable and so are not classified as flammable solids. 

2.7.4.2. 

Screening procedures and waiving of testing 

In  general,  a  possible  classification  as  a  flammable  solid  should  be  considered  for  any  solid 
organic substance or mixture containing such material. For inorganic material, testing may be 
waived in cases where the substance is fully oxidised or commonly known to be not flammable 
(i.e. stable salts or metal oxides) or where a flammability hazard can be excluded by any other 
scientific reasoning. In many cases, a simple screening test (see section 2.7.4.4) can be used to 
determine whether a solid should be classified as flammable. Solid substances and mixtures are 
classified as flammable according to their burning behaviour. 

The test method as described in Part III, section 33.2.4.3.1 in the UN-MTC should be applied for 
screening purposes. Alternatively, the burning index (referred to as ‘class number’ in VDI 2263) 
as obtained from the Burning Behaviour test (VDI 2263, part 1) may be used. If a burning index 
of 3 or less is found, the substance or mixture should not be classified as a flammable solid and 
no further testing is required. However, if smouldering or a flame is observed, the full test must 
be carried out. 

2.7.4.3. 

Classification criteria 

The classification criteria are identical to the GHS system. 

Annex I: 2.7.2.1. Powdered, granular or pasty substances or mixtures (except powders of 
metals or metal alloys – see 2.7.2.2) shall be classified as readily combustible solids when 
the time of burning of one or more of the test runs, performed in accordance with the test 
method described in Part III, sub-section 33.2.1, of the UN RTDG, Manual of Tests and 
Criteria, is less than 45 seconds or the rate of burning is more than 2,2 mm/s. 

2.7.2.2. Powders of metals or metal alloys shall be classified as flammable solids when they 
can be ignited and the reaction spreads over the whole length of the sample (100 mm) in 
10 minutes or less. 

2.7.2.3. A flammable solid shall be classified in one of the two categories for this class using 
Method N.1 as described in 33.2.1 of the UN RTDG, Manual of Tests and Criteria in 
accordance with Table 2.7.1: 

 
 
 
 
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Table 2.7.1  Criteria for flammable solids 

Category  Criteria 

Burning rate test 

Substances and mixtures other than metal powders: 

(a) 

(b) 

wetted zone does not stop fire and 

burning time < 45 seconds or burning rate > 2,2 mm/s 

Metal powders: 

burning time  5 minutes 

Burning rate test 

Substances and mixtures other than metal powders: 

(a) 

(b) 

wetted zone stops the fire for at least 4 minutes and 

burning time < 45 seconds or burning rate > 2,2 mm/s 

Metal powders: 

burning time > 5 minutes and  10 minutes 

1 

2 

[…] 

Note 2: 

Aerosols shall not be classified as flammable solids; see section 2.3. 

2.7.4.4. 

Testing and evaluation of hazard information 

For safety reasons, it is advisable to test for explosive and self-reactive properties first and to 
rule out pyrophoric behaviour before performing this test. The classification test is described in 
Part  III,  section  33.2.4.3.2  of  the  UN-MTC.  The  sample  should  be  tested  in  its  commercially 
relevant form. Special care has to be taken that the sample forms an unbroken strip or powder 
train in the test mould. Large pieces that do not fit into the mould should be gently crushed. For 
pasty or sticking substances, it may be helpful to line the mould with a thin plastic foil which is 
withdrawn  after  having  formed  the  train.  A  small  gas  burner  with  a  non-luminous  flame  has 
proven  most  practical  as  ignition  source;  see  UN-MTC  section  33.2.4.3.1.  To  detect  also 
smouldering  behaviour,  it  is  advisable  to  dim  the  light  in  the  laboratory  hood  during  the 
experiment. 

Classification is based upon the fastest burning rate / shortest burning time obtained in six test 
runs, unless a positive result is observed earlier. For substances and mixtures other than metal 
powders,  the  category  is  assigned  depending  on  whether  the  wetted  zone  is  able  to  stop  the 
flame: if the flame passes the wetted zone in at least one trial, category 1 is assigned. 

In case the flame propagates rapidly (less than 20 seconds for 100 mm), it is advisable to check 
for explosive or self-reactive properties. Another possible reason is the presence of flammable 
liquids in the sample, in which case, labelling with the statement EUH018 — ‘In use, may form 
flammable/explosive vapour-air mixture’ following Article 25 of CLP is applicable. 

2.7.4.5. 

Decision logic 

Classification of flammable solids is done according to 2.4 (equivalent to the decision logic 2.7 
in GHS v.7). 

 
 
 
 
 
 
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NOTE:  The  person  responsible  for  the  classification  of  flammable  solids  should  be 
experienced in this field and be familiar with the criteria for classification. 

Figure 2.4 Decision logic for flammable solids (Decision logic 2.7 of GHS) 

The substance/mixture is a solid 

Screening test 

Negative 

Not classified 

Positive 

Burning rate test: 

a.

For substances or mixtures other than metal powders: 

No 

Burning time < 45 s or burning rate > 2.2 mm/s? 

b. Metal powders: Burning time  10 min? 

Yes 

Not classified 

Category 1 

a.

For substances or mixtures other than metal powders: 

No 

Does the wetted zone stop propagation of the flame? 

b. Metal powders: Burning time > 5 min? 

Danger 

Yes 

Category 2 

Warning 

 
 
 
 
 
 
 
 
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2.7.5.  Hazard communication for flammable solids 

2.7.5.1. 
statements 

Pictograms, signal words, hazard statements and precautionary 

Annex I: 2.7.3. Table 2.7.2  Label elements for flammable solids 

Classification 

Category 1 

Category 2 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

H228: Flammable Solid 

H228: Flammable Solid 

Precautionary Statement Prevention 

P210 

P240 

P241 

P280 

P210 

P240 

P241 

P280 

Precautionary Statement Response 

P370 + P378 

P370 + P378 

Precautionary Statement Storage 

Precautionary Statement Disposal 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.7.6.  Relation to transport classification 

Division  4.1  within  Class  4  of  the  UN  RTDG  Model  Regulations  covers  flammable  solids,  solid 
desensitised explosives, self-reactive substances (liquids or solids) and polymerizing substances 
and  mixtures.  If  a  transport  classification  according  to  the  modal  transport  regulations  (ADR, 
RID,  ADN  and  IMDG  Code,  ICAO  TI)  is  available  it  should  be  kept  in  mind  that  transport 
classification is based on prioritisation of hazards (see the UN RTDG Model Regulations, section 
2.0.3)  and  that  flammable  solids  have  a  relatively  low  rank  in  the  precedence  of  hazards. 
Therefore, the translation from transport classification to CLP should be only done if a transport 
classification  for  a  flammable  solid  is  explicitly  available.  The  conclusion  that  a  substance  or 
mixture not classified as a flammable solid for transport should not be classified as a flammable 
solid  according  to  CLP  is,  in  general,  not  correct.  See  Annex  I  for  additional  information  on 
transport classification in relation to CLP classification. 

 
 
 
 
 
 
 
 
 
 
 
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2.7.7.  Example of classification for flammable solids 

2.7.7.1. 
criteria 

Example of substances and mixtures fulfilling the classification 

The following example shows a classification based on test data: 

TEST SUBSTANCE: ‘FLAMMALENE’ (ORGANIC MATERIAL, SOLID) 

Screening test (VDI 2263, part 1):  

burning index: 5 (burning with an open flame or 
emission of sparks)  

Conclusion: Substance is candidate for classification as a flammable solid, further testing 
required. 

UN Test N.1 (Test method for readily 
combustible solids): 

Burning times for a distance of 100 mm (6 runs): 44 
s; 40 s; 49 s; 45 s; 37 s; 41 s. 

Shortest burning time is less than 45 s; substance is 
a flammable solid. 

Wetted zone stops the fire, no reignition. 

Conclusion: Classify as flammable solid, category 2. 

2.7.7.2. 
classification criteria 

Example of substances and mixtures not fulfilling the 

Many inorganic salts and oxides are not flammable such as NaCl, NaBr, KI, FeO, MnO etc. 

Urea or phthalic acid anhydride are examples of organic substances that would not be 
classified as flammable solids. 

2.7.8.  References 

VDI 2263, part 1, 2022, Dust fires and dust explosions - Hazards - assessment - safety measures 
- Safety-related parameters of bulk goods  

2.8.  SELF-REACTIVE SUBSTANCES AND MIXTURES 

2.8.1.  Introduction 

The criteria for ‘Self-reactive substances and mixtures’ are found in CLP Annex I, section 2.8 and 
are identical to those in chapter 2.8 of GHS. 

In  general,  substances  or  mixtures  classified  as  self-reactive  substances  and  mixtures  can 
decompose strongly exothermically when 50 kg are exposed to temperatures of 75 °C or lower 
depending on the SADT of the substance or mixture. 

Self-reactive  substances  and  mixtures  display  a  very  wide  range  of  properties.  The  most 
hazardous type is TYPE A of self-reactive substances and mixtures that, based on their violent 
decomposition  behaviour,  are  too  dangerous  to  transport  commercially  though  they  can  be 
stored  safely  with  appropriate  precautions.  At  the  other  end  of  the  scale  this  classification 
includes substances and mixtures that only decompose very slowly at temperatures well above 
the normal storage and transport temperatures (e.g. 75 °C). 

The  decomposition  of  self-reactive  substances  and  mixtures  can  be  initiated  by  heat,  contact 
with  catalytic  impurities  (e.g.  acids,  heavy-metal  compounds,  and  bases),  friction,  or  impact. 

 
 
 
 
 
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The rate of decomposition increases with temperature and varies with the substance or mixture. 
Decomposition, particularly if no ignition occurs, may result in the production of toxic gases or 
vapours. For certain self-reactive substances and mixtures, the temperature must be controlled 
during  storage  and  handling.  Some  self-reactive  substances  and  mixtures  may  decompose 
explosively,  particularly  if  confined.  This  characteristic  may  be  modified  by  the  addition  of 
diluents  or  by  the  use  of  appropriate  packaging.  Some  self-reactive  substances  and  mixtures 
burn vigorously.  

Additional  hazardous  properties,  resulting  in  subsidiary  labelling,  are  indicated  in  the  list  of 
already  classified  self-reactive  substances  and  mixtures  included  in  the  UN  RTDG  Model 
Regulations, section 2.4.2.3.2.3. 

Commercial  self-reactive  substances  and  mixtures  are  commonly  formulated  by  dilution  with 
compatible solid and liquid substances. 

2.8.2.  Definitions and general considerations for classification of self-

reactive substances and mixtures 

In CLP the following definition is given for self-reactive substances and mixtures: 

Annex I: 

2.8.1.1. Self-reactive substances or mixtures are thermally unstable liquid or solid 
substances or mixtures liable to undergo a strongly exothermic decomposition even without 
participation of oxygen (air). This definition excludes substances and mixtures classified 
according to this Part as explosives, organic peroxides or as oxidising. 

2.8.1.2. A self-reactive substance or mixture is regarded as possessing explosive properties 
when in laboratory testing the formulation is liable to detonate, to deflagrate rapidly or to 
show a violent effect when heated under confinement. 

General considerations 

Annex I: 2.8.3. Hazard communication 

Type G has no hazard communication elements assigned but shall be considered for 
properties belonging to other hazard classes. 

2.8.3.  Relation to other physical hazards 

Neither  the  burning  properties  nor  the  sensitivity  to  impact  and  friction  form  part  of  the 
classification procedure for self-reactive substances and mixtures in CLP. These properties may 
be of importance in safe handling of self-reactive substances and mixtures (see additional tests 
in section 2.8.4.4). 

In addition, the explosive properties do not have to be  determined according to CLP Annex I, 
section 2.1, because explosive properties are incorporated in the classification as self-reactive 
substances  and  mixtures,  see  CLP  Annex  I,  section  2.8.2.1  (a).  Note  that  substances  and 
mixtures may have explosive properties when handled under higher confinement. 

2.8.4.  Classification of substances and mixtures as self-reactive substances 

and mixtures 

2.8.4.1. 

Identification of hazard information 

The classification of a self-reactive substance or mixture in one of the seven categories ‘types A 
to G’ is dependent on its detonation, deflagration and thermal explosion properties, its response 
to heating under confinement, its explosive power and the concentration and the type of diluent 
added to desensitise the substance or mixture. Specifications of acceptable diluents that can be 
used safely are given in the UN RTDG Model Regulations, section 2.4.2.3.5. 

 
 
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The classification of a self-reactive substance or mixture as type A, B or C is also dependent on 
the  type  of  packaging  in  which  the  substance  or  mixture  is  tested  as  it  affects  the  degree  of 
confinement  to  which  the  substance  or  mixture  is  subjected.  This  has  to  be  considered  when 
handling  the  substance  or  mixture;  stronger  packaging  may  result  in  more  violent  reactions 
when  the  substance  or  mixture  decomposes.  This  is  why  it  is  important  that  storage  and 
transport is done in packaging, allowed for the type of self-reactive substance and mixture, that 
conforms  the  requirements  of  the  UN-packaging  or  IBC  instruction  (P520/IBC520)  or  tank 
instruction (T23). 

2.8.4.2. 

Screening procedures and waiving of testing 

The CLP text comprises the following screening considerations. 

Annex I: 2.8.4.2     Additional Classification Considerations 

The classification procedures for self-reactive substances and mixtures need not be applied 
if: 

(a) There are no chemical groups present in the molecule associated with explosive or self 

reactive properties. Examples of such groups are given in Tables A6.1 and A6.236 in 
Appendix 6 of the UN RTDG, Manual of Tests and Criteria; or  

(b) For a single organic substance or a homogeneous mixture of organic substances, the 

estimated SADT for a 50 kg package is greater than 75 o C or the exothermic 
decomposition energy is less than 300J/g. The onset temperature and decomposition 
energy can be estimated using a suitable calorimetric technique (see Part II, sub-section 
20.3.3.3 of the UN RTDG, Manual of Tests and Criteria). 

Self-reactive substances are, for example, compounds containing the following chemical groups: 

a.  Aliphatic azo compounds (-C-N=N-C-); 

b.  Organic azides (-C-N3); 

c.  Diazonium salts (-CN2

+Z-); 

d.  N-nitroso compounds (-N-N=O); and 

e.  Aromatic sulfohydrazides (-SO2-NH-NH2). 

This list is not exhaustive and substances with other reactive groups, combination of groups and 
some mixtures of substances may have similar properties. Additional guidance on substances, 
which may have self-reactive properties, is given in Appendix 6, section 5.1 of the UN-MTC. 

For examples of chemical groups associated with explosive properties please refer to the 
screening procedure under explosives, see section 2.1.4.2. 

2.8.4.3. 

Classification criteria 

According to CLP, substances and mixtures must be considered for classification in this hazard 
class as a self-reactive substance or mixture unless: 

Annex I:  

2.8.2.1. Any self-reactive substance or mixture shall be considered for classification in this 
class as a self-reactive substance or mixture unless: 

(a) they are explosives, according to the criteria given in 2.1; 

36 This note is not part of the legal text: following an update of Appendix 6 of the UN-MTC, the correct table reference is 
A6.3 instead of A6.2 as indicated in the CLP Regulation. 

 
 
 
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(b) they are oxidising liquids or solids, according to the criteria given in 2.13 or 2.14, except 

that mixtures of oxidising substances, which contain 5 % or more of combustible organic 
substances shall be classified as self-reactive substances according to the procedure 
defined in 2.8.2.2; 

(c) they are organic peroxides, according to the criteria given in 2.15; 

(d) their heat of decomposition is less than 300 J/g; or 

(e) their self-accelerating decomposition temperature (SADT) is greater than 75 °C for a 50 

kg package(1)  

2.8.2.2. Mixtures of oxidising substances, meeting the criteria for classification as oxidising 
substances, which contain 5 % or more of combustible organic substances and which do not 
meet the criteria mentioned in (a), (c), (d) or (e) in 2.8.2.1, shall be subjected to the self-
reactive substances classification procedure;  

Such a mixture showing the properties of a self-reactive substance type B to F (see 2.8.2.3) 
shall be classified as a self-reactive substance. 

[…] 

(1) See UN RTDG, Manual of Test and Criteria, sub-sections 28.1, 28.2, 28.337 and Table 28.3. 

In  the  CLP  decision  logic  (see  section  2.8.4.5),  classification  of  self-reactive  substances  or 
mixtures is based on performance-based testing in both small-scale tests and, where necessary, 
some larger scale tests with the substance or mixture in its packaging. The concept of ‘intrinsic 
properties’ is, therefore, not necessarily, applicable to this hazard class. 

Self-reactive substances or mixtures are classified in one of the seven categories of ‘types A to 
G’ according to the classification criteria given in CLP Annex I, section 2.8.2.3. The classification 
principles are given in the decision logic in CLP Annex I, Figure 2.8.1 (see section 2.8.4.5) and 
the Test Series A to H, as described in the Part II of the UN-MTC, should be performed. 

37 This note is not part of the legal text: UN-MTC sub-sections 28.4 includes Test Series H description (SADT texts). 

 
 
 
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Annex I: 2.8.2.3. Self-reactive substances and mixtures shall be classified in one of the 
seven categories of ‘types A to G’ for this class, according to the following principles: 

(a) any self-reactive substance or mixture which can detonate or deflagrate rapidly, as 

packaged, shall be defined as self-reactive substance TYPE A; 

(b) any self-reactive substance or mixture possessing explosive properties and which, as 

packaged, neither detonates nor deflagrates rapidly, but is liable to undergo a thermal 
explosion in that package shall be defined as self-reactive substance TYPE B; 

(c) any self-reactive substance or mixture possessing explosive properties when the substance 

or mixture as packaged cannot detonate or deflagrate rapidly or undergo a thermal 
explosion shall be defined as self-reactive substance TYPE C; 

(d) any self-reactive substance or mixture which in laboratory testing: 

(i) detonates partially, does not deflagrate rapidly and shows no violent effect when 

heated under confinement; or 

(ii) does not detonate at all, deflagrates slowly and shows no violent effect when 

heated under confinement; or 

(iii) does not detonate or deflagrate at all and shows a medium effect when heated 

under confinement; 

shall be defined as self-reactive substance TYPE D; 

(e) any self-reactive substance or mixture which, in laboratory testing, neither detonates nor 
deflagrates at all and shows low or no effect when heated under confinement shall be 
defined as self-reactive substance TYPE E; 

(f) any self-reactive substance or mixture which, in laboratory testing, neither detonates in 
the cavitated state nor deflagrates at all and shows only a low or no effect when heated 
under confinement as well as low or no explosive power shall be defined as self-reactive 
substance TYPE F; 

(g) any self-reactive substance or mixture which, in laboratory testing, neither detonates in 

the cavitated state nor deflagrates at all and shows no effect when heated under 
confinement nor any explosive power, provided that it is thermally stable (SADT is 60 oC 
to 75 oC for a 50 kg package), and, for liquid mixtures, a diluent having a boiling point not 
less than 150 oC is used for desensitisation shall be defined as self-reactive substance 
TYPE G. If the mixture is not thermally stable or a diluent having a boiling point less than 
150 oC is used for desensitisation, the mixture shall be defined as self-reactive substance 
TYPE F. 

Where the test is conducted in the package form and the packaging is changed, a further test 
shall be conducted where it is considered that the change in packaging will affect the outcome 
of the test. 

A list of currently classified self-reactive substances and mixtures is included in the UN RTDG 
Model Regulations, section 2.4.2.3.2.3. 

2.8.4.4. 

Testing and evaluation of hazard information 

2.8.4.4.1. 

Thermal stability and temperature control 

In  addition  to  the  classification  tests  given  in  decision  logic  Figure  2.8.1  of  CLP,  the  thermal 
stability of the self-reactive substances and mixtures has to be assessed to determine the SADT. 

The  SADT  is  defined  as  the  lowest  temperature  at  which  self-accelerating  decomposition  of  a 
substance or mixture may occur in the packaging as used in transport, handling and storage. It 
should be emphasised that the SADT is dependent on the nature of the self-reactive substance 
or  mixture  itself,  together  with  the  volume  and  heat-loss  characteristics  of  the  packaging  or 

 
 
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vessel in which the substance or mixture is handled. The temperature at which self-accelerating 
decomposition occurs decreases: 

•  as the size of the packaging or vessel increases; and 

•  with increasing efficiency of the insulation on the package or vessel. 

The  SADT  is  a  measure  of  the  combined  effect  of  the  ambient  temperature,  decomposition 
kinetics,  package  size  and  the  heat  transfer  properties  of  the  substance  or  mixture  and  its 
packaging. 

There  is  no  relation  between  the  SADT  of  a  self-reactive  substance  and  mixture  and  its 
classification  in  one  of  the  seven  categories  ‘types  A  to  G’.  The  SADT  is  used  to  derive  safe 
handling,  storage  and  transport  temperatures  (control  temperature)  and  alarm  temperature 
(emergency temperature). 

Depending on its SADT, a self-reactive substance or mixture needs temperature control and the 
criteria as given in CLP Annex I, section 2.8.2.4, consist of the following elements: 

1.  Self-reactive substances and mixtures need to be subjected to temperature control 

when the SADT is ≤ 55 ° C. 

2.  Derivation of control and emergency temperatures: 

Type of receptacle  SADT* 

Control temperature 

Emergency temperature 

Single packaging 
and IBC’s 

20 °C or less 

20 °C below SADT 

10 °C below SADT 

over 20 °C to 35 °C 

15 °C below SADT 

10 °C below SADT 

over 35 °C 

10 °C below SADT 

5 °C below SADT 

Tanks 

< 50 °C 

10 °C below SADT 

5 °C below SADT 

*i.e. the SADT of the substance/mixture as packaged for transport, handling and storage. 

The SADT is only valid for the substance or mixture as tested and when handled properly. Mixing 
the  self-reactive  substances  and  mixtures  with  other  chemicals  or  contact  with  incompatible 
materials (including incompatible packaging or vessel material) may reduce the thermal stability 
due to catalytic decomposition and lower the SADT. This may increase the risk of decomposition 
and has to be avoided. 

2.8.4.4.2. 

Additional consideration and testing 

Explosive properties 

The sensitivity of self-reactive substances and mixtures to impact (solids and liquids) and friction 
(solids only) may be of importance for the safe handling of the substances and mixtures, in the 
event  that  these  substances  and  mixtures  have  pronounced  explosive  properties  (e.g.  rapid 
deflagration  and/or  violent  heating  under  confinement).  Test  methods  to  determine  these 
properties are described in Test Series 3 (a) (ii) and 3 (b) (i) of the UN-MTC. This information 
may be documented in the SDS. 

Burning properties 

Although  there  are  currently  no  dedicated  storage  guidelines  for  self-reactive  substances  and 
mixtures  (although  in  some  countries  under  development),  often  the  regulations  for  organic 
peroxides  are  referred  to.  For  storage  classification  the  burning  rate  is  commonly  used,  see 
section 2.15 on organic peroxides. 

Flash point 

The flash point for liquid self-reactive substances or mixtures is only relevant in the temperature 
range where the product is thermally stable. Above the SADT of the self-reactive substance or 
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NOTE:  In  case  a  flash  point  determination  seems  reasonable  (expected  flash  point  below 
the SADT) a test method using a small amount of sample is recommended. In case the self-
reactive substance or mixture is diluted or dissolved, the diluent may determine the flash 
point. 

Auto-ignition temperature 

The determination of the auto-ignition temperature is not relevant for self-reactive substances 
and mixtures, because the vapours decompose during the execution of the test. Available test 
methods  are  for  non-decomposing  vapour  phases.  Auto-ignition  of  vapours  of  self-reactive 
substances or mixtures when they decompose, can never be excluded. This information should 
be documented in the SDS. 

Self-ignition temperature 

The determination of the self-ignition temperature (test applicable for solids) is not relevant. 

The thermal stability of self-reactive substances and mixtures is quantitatively given by the 
SADT test.  

Control and Emergency temperatures 

The  Control  and  Emergency  temperatures  are  based  on  the  SADT  as  determined  by  UN  Test 
Series H. In UN Test Series H.2 and H.3, the heat loss applied in calculating the SADT should be 
representative  for  the  packaging,  IBC,  tank  or  vessel  in  which  the  substance  or  mixture  is 
handled or stored. In UN Test H.4, the Dewar vessel used is supposed to be representative for 
the substance or mixture handled in packages. For handling of the substance or mixture in larger 
quantities (IBCs/tanks/vessels etc.) and/or in better (thermally) insulated containers under more 
thermally insulated conditions, the SADT has to be determined for that quantity with the given 
degree of insulation. From that SADT the Control and Emergency temperatures can be derived 
(see also section 2.8.4.4.1). 

2.8.4.4.3. 

Additional classification considerations 

Currently,  the  following  properties  are  not  incorporated  in  the  classification  of  self-reactive 
substances and mixtures under CLP: 

•  mechanical sensitivity i.e. impact and friction sensitivity (for handling purposes); 

•  burning properties (for storage purposes); 

• 

flash point for liquids; and 

•  burning rate for solids. 

In addition to the GHS criteria CLP mentions that: 

Annex I: 2.8.2.2  

[…] 

Where the test is conducted in the package form and the packaging is changed, a further 
test shall be conducted where it is considered that the change in packaging will affect the 
outcome of the test. 

Please note that polymerising substances do not fulfil the criteria for classification as self-reactive 
substances  and  mixtures.  In  transport  regulations,  they  are  classified  as  polymerising 
substances. These substances are not contained in GHS and therefore not incorporated in CLP. 

2.8.4.5. 

Decision logic 

Classification of self-reactive substances and mixtures is done according to decision logic 2.8 as 
included in GHS. 

 
 
 
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NOTE: The person responsible for the classification of self-reactive substances and mixtures 
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Annex I: Figure 2.8.1 Self-reactive substances and mixtures 

 
 
 
 
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2.8.5.  Hazard communication for self-reactive substances and mixtures 

2.8.5.1. 
statements 

Pictograms, signal words, hazard statements and precautionary 

According to CLP the following label elements must be used for substances and mixtures meeting 
the criteria for this hazard class: 

Annex I:  Table 2.8.1 

Label elements for self-reactive substances and mixtures 

Classification 

Type A 

Type B 

Type C & D 

Type E & F 

Type G(1) 

GHS pictograms 

Signal Word 

Danger 

Danger 

Danger 

Warning 

Hazard Statement 

H240: 

H241: 

H242: 

Heating may 

Heating may 

Heating may 

cause an 

cause a fire or 

cause a fire 

explosion 

explosion 

H242: 
Heating 

may cause a 
fire 

Precautionary 
statement 

Prevention 

Precautionary 
statement 

Response 

Precautionary 
statement 

Storage 

Precautionary 
statement 

Disposal 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P370 + P372 
+ P380 + 
P373 

P370 + P380 
+ P375 
[+P378](2) 

P370 + P378  P370 + P378 

P403 

P411 

P420 

P501 

P403 

P411 

P420 

P501 

P403 

P411 

P420 

P501 

P403 

P411 

P420 

P501 

There are 
no label 
elements 
allocated 
to this 
hazard 
category 

 
 
 
 
 
 
 
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(1) Type G has no hazard communication elements assigned but should be considered for properties 
belonging to other hazard classes. 

(2) See the introduction to Annex IV for details on the use of square brackets. 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.8.6.  Relation to transport classification  

Division  4.1  within  Class  4  of  the  UN  RTDG  Model  Regulations  covers  flammable  solids,  self-
reactive substances, solid desensitised explosives and polymerising substances (not being part 
of GHS and CLP). A list of already classified self-reactive substances is included in the UN RTDG 
Model Regulations,  section 2.4.2.3.2.3.  This table includes  self-reactive  substances of various 
types from type B to type F. See Annex I for additional information on transport classification in 
relation to CLP classification. 

2.8.7.  Example of classification for self-reactive substances and mixtures 

2.8.7.1. 
criteria 

Example of substances and mixtures fulfilling the classification 

Substance to be classified: NP 

Molecular formula: not applicable  

The substance has: 

•  an energy content of 1452 kJ/kg; and 

•  a SADT of 45 °C (in 50 kg package); 

and according to CLP Annex I, section 2.8.2.1, consequently it has to be considered for 
classification in the hazard class self-reactive substances and mixtures. 

Test results and classification according to CLP Annex I, Figure 2.8.1 for self-reactive 
substances and mixtures and the UN-MTC, Part II, are as follows: 

CLASSIFICATION TEST RESULTS 

1. Name of the self-reactive substance or mixture:  NP 

2. General data 

2.1. 

Composition 

NP, technically pure 

2.2. 

Molecular formula 

Not applicable 

2.3. 

Physical form 

Solid, fine powder 

2.4. 

Colour 

2.5. 

Density (apparent) 

3. Detonation (Test Series A) 

Brown 

460 kg/m3 

Box 1 of the decision logic 

Does the substance propagate a detonation? 

3.1. 

Method 

UN Test A.1: BAM 50/60 steel tube test 

3.2. 

Sample conditions 

Technically pure substance 

 
 
 
 
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CLASSIFICATION TEST RESULTS 

3.3. 

Observations 

Fragmented part of the tube: 12, 18cm 

3.4. 

Result 

3.5. 

Exit 

4. Deflagration (Test Series C) 

No 

1.3 

Box 5 of the decision logic 

Does the substance propagate a deflagration? 

4.1. 

Method 1 

Time/pressure test (UN Test C.1) 

4.1.1. 

Sample conditions 

Ambient temperature 

4.1.2.  Observations 

498, 966, 3395 ms 

4.1.3.  Result 

Yes, slowly 

4.2. 

Method 2 

Deflagration test (UN Test C.2) 

4.2.1. 

Sample conditions 

Temperature: 20 °C 

4.2.2.  Observations 

Deflagration rate: 0.90, 0.87 mm/s 

4.2.3.  Result 

4.3. 

Final result 

4.4. 

Exit 

Yes, slowly 

Yes, slowly 

5.2 

5. Heating under confinement (Test Series E) 

Box 8 of the decision logic: 

What is the effect of heating it under defined 
confinement? 

5.1. 

Method 1 

Koenen test (UN Test E.1) 

5.1.1. 

Sample conditions 

5.1.2.  Observations 

Limiting diameter: < 1.0 mm, fragmentation 
type ‘A’ 

5.1.3.  Result 

Low 

5.2. 

Method 2 

Dutch pressure vessel test (test E.2) 

5.2.1. 

Sample conditions 

5.2.2.  Observations 

5.2.3.  Result 

5.3. 

Final result 

5.4. 

Exit 

Limiting diameter: <1.0 mm (with 10 g), 1.0 
mm (50 g) 

Low 

Low 

8.3 

 
 
 
 
 
 
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CLASSIFICATION TEST RESULTS 

6. Thermal stability (outside of the decision logic) 

6.1. Method 

Heat accumulation storage test (UN Test H.4) 

6.2. 

Sample conditions: 

Mass 232.5 g. Half life time of cooling of 
Dewar vessel with 400 ml water: 10.0 h 
(representing substance in package) 

6.3. Observations 

Self-accelerating decomposition at 45 °C 

6.4. Result 

7. General remarks 

8. Final classification 

Hazard / hazard class: 

Label 

Signal word 

No self-accelerating decomposition at 40 °C 

SADT 45 °C (in 50 kg package) 

The decision logic is given in Figure 2.5 

Self-reactive substance, Type D, solid, 
temperature controlled 

Flame (GHS02) 

Danger 

Hazard statement 

H242: Heating may cause a fire 

Temperature control 

Needed based on SADT (45 °C, in package) 

Control temperature* 

35 °C (in package) 

Emergency temperature* 

40 °C (in package) 

*See UN-MTC, table 28.3. 

 
 
 
 
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Figure 2.5 Decision logic for self-reactive substance example: NP, technically pure 

 
 
 
 
 
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2.9.  PYROPHORIC LIQUIDS 

2.9.1.  Introduction 

The  criteria  for  ‘Pyrophoric  liquids’  are  found  in  CLP  Annex  I,  section  2.9  and  are  identical  to 
those in chapter 2.9 of GHS. 

Pyrophoricity,  i.e.  the  ability  to  spontaneously  ignite  in  air,  is  the  result  of  a  reaction  of  a 
substance or mixture with the oxygen in the air and it is a very dangerous property. The reaction 
is  exothermic  and  has  the  particularity  that  it  starts  spontaneously,  i.e.  without  the  aid  of  a 
supplied spark, flame, heat or other energy source. Another way of saying this is that the auto-
ignition  temperature  for  a  pyrophoric  substance  or  mixture  is  lower  than  room  (ambient) 
temperature. 

2.9.2.  Definitions and general considerations for classification of pyrophoric 

liquids 

The definition in CLP for pyrophoric liquids is as follows: 

Annex I: 2.9.1.     Definition  

Pyrophoric liquid means a liquid substance or mixture which, even in small quantities, is 
liable to ignite within five minutes after coming into contact with air. 

2.9.3.  Relation to other physical hazards 

Pyrophoric substances and mixtures will react spontaneously with air already in small amounts 
and more  or less instantaneously (within minutes). This differentiates  them from  self-heating 
substances  and  mixtures,  which  also  react  spontaneously  with  air  but  only  when  in  larger 
amounts  and  after  an  extended  period  of  time  (hours  or  days).  While  liquids  in  themselves 
generally do not exhibit self-heating properties due to the limited  contact with air (which can 
occur only at the surface), liquids that are adsorbed onto solid particles should, in general, be 
considered for classification in the hazard class self-heating substances and mixtures, see section 
2.11. 

Pyrophoricity may be expected for certain reactive metals and some of their compounds (e.g. 
hydrides and other organo-metal compounds). Many of these substances and mixtures will also 
react  vigorously  with  water  under  the  production  of  flammable  gases.  Such  substances  and 
mixtures  may  therefore  be  classified  in  the  hazard  class  substances  and  mixtures  which  in 
contact with water emit flammable gases in addition, see section 2.12. It should be noted in this 
context  that  water-reactive  substances  and  mixtures  may  also  to  some  extent  react  with  the 
humidity  in  air,  although  such  a  reaction  is  seldom  vigorous.  A  substance  or  mixture  that 
spontaneously  ignites  in  air  in  accordance  with  the  test  procedures  is  to  be  considered 
pyrophoric, regardless of the reaction mechanism. 

Liquids not classified as pyrophoric but that can burn may belong to the hazard class flammable 
liquids depending on their flash point and ability to sustain combustion, see section 2.6. 

2.9.4.  Classification of substances and mixtures as pyrophoric liquids 

2.9.4.1. 

Identification of hazard information 

Since  the  tests  to  determine  pyrophoricity  are  simple  and  require  no  special  equipment,  see 
section 2.9.4.4 below, there is in general no reason to go to data sources instead of performing 
the  tests.  Furthermore,  the  possibilities  of  waiving  the  tests  are  ample  both  for  known 
pyrophores and for substances and mixtures known not to be pyrophoric, see  section  2.9.4.2 
below. If information nevertheless is taken from literature or other data sources, it is of utmost 
importance  that  the  correct  physical  form  is  considered,  see  section  2.0.4.  Naturally,  all  data 
sources should be carefully evaluated with regard to reliability and scientific validity. 

 
 
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2.9.4.2. 

Screening procedures and waiving of testing 

Organo-metals and organo-metalloids may be suspected of being pyrophores, as well as their 
derivatives. Also, organo-phosphines and their  derivatives, hydrides and their derivatives and 
haloacetylene  derivatives  may  show  pyrophoricity.  There  are  also  pyrophoric  substances  or 
mixtures that do not belong to the above-mentioned groups of chemicals, i.e. the list above is 
not exhaustive. In case of doubt, it should be thoroughly investigated whether a given substance 
or mixture is pyrophoric. More information  on  pyrophoric substances  can be found in sources 
such as Bretherick’s Handbook of Reactive Chemical Hazards (Urben, 2007). 

In case a liquid is known from practical handling to be pyrophoric, no testing is necessary. Such 
liquids  are  classified  as  pyrophoric  liquids  without  testing.  This  would  also  be  the  case  if  the 
liquid spontaneously ignites upon opening of the receptacle when trying to perform the tests for 
classification. 

According to the additional classification considerations in CLP: 

Annex I: 2.9.4.1. The classification procedure for pyrophoric liquids need not be applied 
when experience in manufacture or handling shows that the substance or mixture does not 
ignite spontaneously on coming into contact with air at normal temperatures (i.e. the 
substance or mixture is known to be stable at room temperature for prolonged periods of 
time (days)). 

2.9.4.3. 

Classification criteria 

Section 2.9.2.1 of Annex I to CLP specifies the classification criteria: 

Annex I: Table 2.9.1 

Criteria for pyrophoric liquids 

Category 

Criteria 

1 

The liquid ignites within 5 min when added to an inert carrier and exposed to 
air, or it ignites or chars a filter paper on contact with air within 5 min. 

2.9.4.4. 

Testing and evaluation of hazard information 

In CLP Annex I, section 2.9.2.1 reference to the test-methods is made: 

Annex I: 2.9.2.1. A pyrophoric liquid shall be classified in a single category for this class 
using test N.3 in part III, sub-section 33.3.1.538 of the UN RTDG, Manual of Tests and 
Criteria according to Table 2.9.1: 

The UN Test N.3 for pyrophoricity is quite simple and sufficiently described in Part III, section 
33.4.5 of the UN-MTC. No special equipment is needed. Essentially, the substance or mixture is 
exposed to air to see if it ignites. For liquids which do not spontaneously ignite when poured, 
the surface in contact with air is increased using a filter paper. Ignition or charring of the filter 
paper  is  regarded  as  a  positive  response  in  the  test,  i.e.  such  a  liquid  is  considered  to  be 
pyrophoric. 

It is important that samples for testing of pyrophoric properties are carefully packed and sealed. 
Furthermore,  the  material  offered  for  testing  should  be  freshly  prepared,  since  the  reactive 

38 This note is not part of the legal text: following an update on the UN-MTC, the correct reference is ‘section 33.4.5’ 
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properties may diminish due to aging or agglomeration. Whenever experiments are to be done 
one should be careful – a pyrophoric substance or mixture may well ignite already upon opening 
the receptacle! 

It should be noted that the mechanism of oxidation is, in general, very complex, and that the 
humidity of air might influence the rate of reaction. Therefore, a false negative may result when 
performing the tests in an extremely dry environment, and this condition must be avoided when 
performing the tests for classification for pyrophoricity. The filter paper test of UN Test N.3 for 
pyrophoric liquids should be carried out at 25 ± 2 °C and a relative humidity of 50 ± 5 % (see 
UN-MTC, section 33.4.5). 

2.9.4.5. 

Decision logic 

Classification of pyrophoric liquids is done according to decision logic 2.9 as included in GHS. 

NOTE:  The  person  responsible  for  the  classification  of  pyrophoric  liquids  should  be 
experienced in this field and be familiar with the criteria for classification. 

Figure 2.6  Decision logic for pyrophoric liquids (Decision logic 2.9 of GHS) 

The substance/mixture is a liquid 

Does it ignite within 5 min when poured into a porcelain 
cup filled with diatomaceous earth or silica gel? 

Yes 

No 

Does it ignite or char a filter paper within 5 min? 

Yes 

No 

Category 1 

Danger 

Category 1 

Danger 

Not 
classified 

 
 
 
 
 
 
 
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2.9.5.  Hazard communication for pyrophoric liquids 

2.9.5.1. 
statements 

Pictograms, signal words, hazard statements and precautionary 

Annex I: 2.9.3 Table 2.9.2 

Label elements for pyrophoric liquids 

Classification 

Category 1 

GHS Pictogram 

Signal Word 

Danger 

Hazard Statement 

H250: Catches fire spontaneously if exposed to air 

Precautionary Statement 
Prevention 

Precautionary Statement 
Response 

Precautionary Statement Storage 

Precautionary Statement Disposal 

P210 

P222 

P231 + P232 

P233 

P280 

P302 + P334 

P370 + P378 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.9.6.  Relation to transport classification 

Division 4.2 within Class 4 of the UN RTDG Model Regulations covers pyrophoric solids, liquids 
and  self-heating  substances  and  mixtures.  UN  Test  N.3  that  is  used  for  classification  for 
pyrophoricity  for  liquids  according  to  CLP  is  also  used  for  classification  in  the  subdivision 
pyrophoric  substances  and  mixtures  in  Division  4.2:  Substances  liable  to  spontaneous 
combustion according to the UN RTDG Model Regulations. The criteria for category 1 according 
to CLP (which is the only category for pyrophoric liquids) and for packing group I in Division 4.2 
according to the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) are also 
exactly the same. Furthermore, all pyrophoric substances and mixtures are assigned to packing 
group I within Division 4.2, which is used exclusively for pyrophoric substances and mixtures. 

Therefore, any liquid assigned to Division 4.2, packing group I according to the modal transport 
regulations  (ADR,  RID,  ADN  and  IMDG  Code,  ICAO  TI)  will  be  classified  in  category  1  of  the 
hazard  class  pyrophoric  liquids  according  to  CLP.  See  Annex  I  for  additional  information  on 
transport classification in relation to CLP classification. 

 
 
 
 
 
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2.9.7.  Examples of classification for pyrophoric liquids 

Please note that the substance and mixture names in this chapter are fictitious. 

2.9.7.1. 
criteria 

Examples of substances and mixtures fulfilling the classification 

2.9.7.1.1. 

Example 1 

Name: 

Pyrpherdine 

Physical state: 

Liquid 

Pyrophoric properties: 

Unknown, therefore the UN Test N.3 of the UN-MTC was applied. 
However, when opening the receptacle to perform the test, 
Pyrpherdine self-ignited spontaneously. 

Classification: 

Pyrophoric liquid, category 1 

2.9.7.1.2. 

Example 2 

Name: 

Qulipyr 

Physical state: 

Liquid 

Pyrophoric properties: 

Unknown, therefore the UN Test N.3 of the UN-MTC was applied. 

Test result: 

When poured according to the test procedure, nothing happened. The 
procedure was repeated six times, each time giving a negative result 
(i.e. no ignition). Therefore, Qulipyr was supplied to a filter paper in 
accordance with the test method. In the second trial the filter paper 
was charred within five minutes. 

Classification: 

Pyrophoric liquid, category 1 

2.9.7.2. 
classification criteria 

Example of substances and mixtures not fulfilling the 

2.9.7.2.1. 

Example 3 

Name: 

Notpyratal 

Physical state: 

Liquid 

Pyrophoric properties: 

Unknown, therefore UN Test N.3 of the UN-MTC was applied. 

Test result: 

When poured according to the test procedure nothing happened in 
either of six trials. Therefore, Notpyratal was supplied to a filter paper 
in accordance with the test method, whereupon no ignition or charring 
occurred in either of three trials. 

Classification: 

Not a pyrophoric liquid 

 
 
 
 
 
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2.9.8.  References 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier. 

2.10. PYROPHORIC SOLIDS 

2.10.1.  Introduction 

The criteria for ‘Pyrophoric solids’ are found in CLP Annex I,  section 2.10 and are identical to 
those in chapter 2.10 of GHS. 

Pyrophoricity,  i.e.  the  ability  to  spontaneously  ignite  in  air,  is  the  result  of  a  reaction  of  a 
substance or mixture with the oxygen in the air and it is a very dangerous property. The reaction 
is  exothermic  and  has  the  particularity  that  it  starts  spontaneously,  i.e.  without  the  aid  of  a 
supplied spark, flame, heat or other energy source. Another way of saying this is that the self-
ignition  temperature  for  a  pyrophoric  substance  or  mixture  is  lower  than  room  (ambient) 
temperature. 

2.10.2.  Definitions and general considerations for classification of pyrophoric 

solids 

The definition in CLP for pyrophoric solids is as follows: 

Annex I: 2.10.1.     Definition  

Pyrophoric solid means a solid substance or mixture which, even in small quantities, is liable 
to ignite within five minutes after coming into contact with air. 

Special consideration on particle size 

Annex I: 2.10.2.1. 

[…] 

Note: The test shall be performed on the substance or mixture in its physical form as 
presented. If, for example, for the purposes of supply or transport, the same chemical is to 
be presented in a physical form different from that which was tested and which is considered 
likely to materially alter its performance in a classification test, the substance shall also be 
tested in the new form. 

The  finer  the  particle  size  of  a  solid,  the  greater  the  area  exposed  to  air  will  be,  and  since 
pyrophoricity is a reaction with the oxygen in air, the particle size will greatly influence the ability 
to  spontaneously  ignite.  Hence,  it  is  very  important  that  pyrophoric  properties  for  solids  are 
investigated  on  the  substance  or  mixture  as  it  is  actually  presented  (including  how  it  can 
reasonably be expected to be used, see Article 8(6) of CLP). This is indicated by the Note in CLP 
Annex I, section 2.10.2.1. 

2.10.3.  Relation to other physical hazards 

Pyrophoric solids will react spontaneously with  air already in small amounts and more or less 
instantaneously  (within  minutes).  This  differentiates  them  from  self-heating  substances  and 
mixtures, which also react spontaneously with air but only when in larger amounts and after an 
extended period of time (hours or days). A solid which is not classified as a pyrophoric solid may 
therefore  belong  to  the  hazard  class  self-heating  substances  and  mixtures,  and  should  be 
considered for classification in that hazard class, see section 2.11. 

Pyrophoricity may be expected for certain reactive metals and some of their compounds (e.g. 
hydrides  and  other  organo-metal  compounds).  Many  of  these  substances  will  also  react 

 
 
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vigorously with water under the production of flammable gases. Such substances may therefore 
be  classified  in  the  hazard  class  substances  and  mixtures  which  in  contact  with  water  emit 
flammable  gases  in  addition  to  pyrophoric  solid  classification,  see  section  2.12.  It  should  be 
noted in this context that water-reactive substances or mixtures may also to some extent react 
with  the  humidity  in  air,  although  such  a  reaction  is  seldom  vigorous.  A  substance  that 
spontaneously  ignites  in  air  in  accordance  with  the  test  procedures  is  to  be  considered 
pyrophoric, regardless of the reaction mechanism. 

Solids  not  classified  as  pyrophoric  may  still  be  able  to  burn  rapidly  if  subjected  to  enough 
initiating energy, such as the flame from a gas burner, to start the reaction. Therefore, they may 
be subject to classification in the hazard class flammable solids, see section 2.7, i.e. they may 
be 'flammable solids'. 

2.10.4.  Classification of substances and mixtures as pyrophoric solids 

2.10.4.1. 

Identification of hazard information 

Since  the  tests  to  determine  pyrophoricity  are  simple  and  require  no  special  equipment,  see 
section 2.10.4.4 below, there is in general no reason to go to data sources instead of performing 
tests. Furthermore, the possibilities of waiving tests are ample both for known pyrophores and 
for  substances  and  mixtures  known  not  to  be  pyrophoric,  see  section  2.10.4.2  below.  If 
information nevertheless is taken from literature or other data sources, it is of utmost importance 
that the correct physical form is considered, see section 2.0.4. Naturally, all data sources should 
be carefully evaluated with regard to reliability and scientific validity. 

2.10.4.2.  Screening procedures and waiving of testing 

Organo-metals and organo-metalloids may be suspected of being pyrophores, as well as their 
derivatives. In addition, organo-phosphines and their derivatives, hydrides and their derivatives, 
haloacetylene  derivatives,  and  complex  acetylides  may  show  pyrophoricity  (Urben,  2007). 
Furthermore, powders or fine particles of metals could be pyrophoric. However, although many 
solid  metallic  substances,  like  e.g.  aluminium,  would  be  suspected  of  being  pyrophoric  when 
considering  their  general  reactivity,  they  form  a  protective  oxide-coat  upon  reaction  with  air. 
This  thin  coat  of  metal  oxide  prevents  the  metal  from  reacting  further,  and  hence  such 
substances may not show pyrophoric behaviour in reality. There are also pyrophoric solids that 
do not belong to the above-mentioned groups of chemicals, i.e. the list above is not exhaustive.  

Since pyrophoric solids ignite spontaneously in air, pyrophoricity is a very dangerous property. 
In case of doubt, it should be thoroughly investigated whether a given solid is pyrophoric. More 
information  on  pyrophoric  solids  can  be  found  in  sources  such  as  Bretherick’s  Handbook  of 
Reactive Chemical Hazards (Urben, 2007). 

In case a solid is known from practical handling to be pyrophoric, no testing is necessary. Such 
solids are classified as pyrophoric solids without testing. This would also be the case if the solid 
spontaneously  ignites  upon  opening  of  the  receptacle  when  trying  to  perform  the  tests  for 
classification. 

According to the additional classification considerations in CLP: 

Annex I: 2.10.4.1. The classification procedure for pyrophoric solids need not be applied 
when experience in manufacture or handling shows that the substance or mixture does not 
ignite spontaneously on coming into contact with air at normal temperatures (i.e. the 
substance or mixture is known to be stable at room temperature for prolonged periods of 
time (days)). 

2.10.4.3.  Classification criteria 

Section 2.10.2.1 of Annex I to CLP specifies the classification criteria: 

 
 
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Annex I: Table 2.10.1 

Criteria for pyrophoric solids 

Category 

Criteria 

1 

The solid ignites within 5 minutes of coming into contact with air. 

2.10.4.4.  Testing and evaluation of hazard information 

In CLP Annex I, section 2.10.2.1 reference to the test-methods are made: 

Annex I: 2.10.2.1. A pyrophoric solid shall be classified in a single category for this class 
using test N.2 in part III, sub-section 33.3.1.439 of the UN RTDG, Manual of Tests and 
Criteria in accordance with Table 2.10.1: 

UN Test N.2 for pyrophoricity is quite simple and sufficiently described in Part III, section 33.4.4 
of the UN-MTC. No special equipment is needed. Essentially the solid is exposed to air to see if 
it ignites.  

It is important that samples for testing of pyrophoric properties are carefully packed and sealed. 
Furthermore,  the  material  offered  for  testing  should  be  freshly  prepared,  since  the  reactive 
properties may diminish due to aging or agglomeration. Whenever experiments are to be done 
one should be careful – a pyrophoric solid may well ignite already upon opening the receptacle! 

It should be noted that the mechanism of oxidation is, in general, very complex, and that the 
humidity of air might influence the rate of reaction. It is known that certain metals will not react 
in dry air, whereas in the presence of moisture the reaction is almost instantaneous (often even 
trace  amounts  of  moisture  are  sufficient).  Therefore,  a  false  negative  may  result  when 
performing the tests in an extremely dry environment, and this condition must be avoided when 
performing the tests for classification for pyrophoricity. 

2.10.4.5.  Decision logic 

Classification of pyrophoric solids is done according to decision logic 2.10 as included in GHS. 

NOTE:  The  person  responsible  for  the  classification  of  pyrophoric  solids  should  be 
experienced in this field and be familiar with the criteria for classification. 

39 This note is not part of the legal text: following an update on the UN-MTC, the correct reference is ‘section 33.4.4’ 
instead of ‘section 33.3.1.4’ as indicated in the CLP Regulation. 

 
 
 
 
 
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Figure 2.7  Decision logic for pyrophoric solids (Decision logic 2.10 of GHS) 

The substance/mixture is a solid 

Does it ignite within 5 min after exposure to air? 

Yes 

No 

Category 1 

Danger 

Not classified 

2.10.5.  Hazard communication for pyrophoric solids 

2.10.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

Annex I: 2.10.3 Table 2.10.2 

Label elements for pyrophoric solids 

Classification 

Category 1 

GHS Pictogram 

Signal Word 

Danger 

Hazard Statement 

H250: Catches fire spontaneously if 
exposed to air 

Precautionary Statement Prevention 

P231 + P232 

P210 

P222 

P233 

P280 

P302 + P335 + P334 

P370 + P378 

Precautionary Statement Response 

Precautionary Statement Storage 

Precautionary Statement Disposal 

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2.10.6.  Relation to transport classification 

Division 4.2 within Class 4 of the UN RTDG Model Regulations covers pyrophoric solids, liquids 
and self-heating substances and mixtures. The UN Tests N.2 that is used for classification for 
pyrophoricity  for  solids  according  to  CLP  is  also  used  for  classification  in  the  subdivision 
pyrophoric  substances  and  mixtures  in  Division  4.2:  substances  liable  to  spontaneous 
combustion according to the UN RTDG Model Regulations. The criteria for category 1 according 
to CLP (which is the only category for pyrophoric solids) and for packing group I in Division 4.2 
according to the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) are also 
exactly the same. Furthermore, all pyrophoric substances and mixtures are assigned to packing 
group I within Division 4.2, which is used exclusively for pyrophoric substances and mixtures. 

Therefore, any solid assigned to Division 4.2, packing group I according to the modal transport 
regulations  (ADR,  RID,  ADN  and  IMDG  Code,  ICAO  TI)  will  be  classified  in  category  1  of  the 
hazard  class  pyrophoric  solids  according  to  CLP.  See  Annex  I  for  additional  information  on 
transport classification in relation to CLP classification. 

2.10.7.  Examples of classification for pyrophoric solids 

Please note that the substance and mixture names in this chapter are fictitious. 

2.10.7.1.  Examples of substances and mixtures fulfilling the classification 
criteria 

2.10.7.1.1.  Example 1 

Name: 

Pyroferil 

Physical state: 

Solid 

Pyrophoric properties:  Pyroferil is known to self-ignite upon contact with air at ambient conditions. 

Classification: 

Pyrophoric solid, category 1 

2.10.7.1.2.  Example 2 

Name: 

Zorapyrole 

Physical state: 

Solid 

Pyrophoric properties:  Unknown, therefore the UN Test N.2 of the UN-MTC was applied. 

Test result: 

When  poured  from  one  meter  height  according  to  the  test  procedure, 
Zorapyrole self-ignited after two minutes already in the first trial. 

Classification: 

Pyrophoric solid, category 1 

2.10.7.2.  Example of substances and mixtures not fulfilling the 
classification criteria 

2.10.7.2.1.  Example 3 

Name: 

Nonopyr 

Physical state: 

Solid 

 
 
 
 
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Pyrophoric properties: 

Nonopyr has been handled extensively in air and has never self-ignited. From 
the chemical structure no pyrophoricity is expected. 

Classification: 

Not a pyrophoric solid 

2.10.7.2.2.  Example 4 

Name: 

Pyronot 

Physical state: 

Solid 

Pyrophoric properties:  Unknown, therefore UN Test N.2 of the UN-MTC was applied. 

Test result: 

When poured from one meter height according to the test procedure no 
ignition occurred within five minutes. The procedure was repeated six times 
and each time the result was negative. 

Classification: 

Not a pyrophoric solid 

2.10.8.  References 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier. 

2.11. SELF-HEATING SUBSTANCES AND MIXTURES 

2.11.1.  Introduction 

The criteria for ‘Self-heating substances and mixtures’ are found in CLP Annex I, section 2.11 
and are identical to those in chapter 2.11 of GHS. 

Self-heating is the result of an exothermic reaction of a substance or mixture with the oxygen 
in the air. Initially, the reaction rate may be very low. However, when the heat produced cannot 
be removed rapidly enough, the substance or mixture will self-heat through heat accumulation, 
with the possible consequence of self-ignition. The phenomenon can occur only where a large 
surface of substance or mixture is in contact with air or oxygen (for example, piles of powders, 
crystals,  splinters,  any  other  rough  surface  etc.).  The  initiation  occurs  usually  at  or  near  the 
centre  of  the  substance  or  mixture  pile  with  the  available  air  in  the  interspace  between  the 
particles. 

2.11.2.  Definitions and general considerations for classification of self-

heating substances and mixtures 

The definitions in CLP for self-heating substances and mixtures are as follows: 

Annex I: 2.11.1.1. A self-heating substance or mixture is a liquid or solid substance or 
mixture, other than a pyrophoric liquid or solid, which, by reaction with air and without energy 
supply, is liable to self-heat; this substance or mixture differs from a pyrophoric liquid or solid 
in that it will ignite only when in large amounts (kilograms) and after long periods of time 
(hours or days). 

2.11.1.2. Self-heating of a substance or a mixture is a process where the gradual reaction of 
that substance or mixture with oxygen (in the air) generates heat. If the rate of heat 

 
 
 
 
 
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production exceeds the rate of heat loss, then the temperature of the substance or mixture 
will rise which, after an induction time, may lead to self-ignition and combustion. 

2.11.3.  Relation to other physical hazards 

Pyrophoric  solids  and  liquids  should  not  be  considered  for  classification  as  self-heating 
substances and mixtures. 

2.11.4.  Classification of substances and mixtures as self-heating 

2.11.4.1. 

Identification of hazard information 

Self-heating is a very complex phenomenon which is influenced by many parameters (some of 
them being volume, temperature, particle shape and size, heat conductivity and bulk density). 
Therefore,  self-heating  behaviour  cannot  be  predicted  from  any  theoretical  model.  In  some 
cases, properties might even differ between material from producers of seemingly identical or 
similar  substances  or  mixtures.  Differences  in  self-heating  behaviour  are  especially  to  be 
anticipated where surface treatment occurs in the production process. Hence, all data sources 
should be carefully evaluated with regard to reliability and scientific validity. 

Self-heating substances and mixtures may include the following: 

•  many organometallic compounds, especially substances or mixtures containing 

transition metals; 

•  many organic substances or mixtures; the tendency to self-heat increases with 

decreasing particle size; 

•  many metals, especially catalysts. 

Since the surface area of a solid substance or mixture exposed to air increases with decreasing 
particle  size,  it  follows  that  particle  size  and  shape  will  greatly  influence  the  potential  of  a 
substance or mixture to self-heat. Therefore, it is very important that self-heating properties for 
solids,  and  especially  powders,  are  determined  for  the  substance  or  mixture  in  the  form  it  is 
supplied and expected to be used. 

2.11.4.2.  Screening procedures and waiving of testing 

Annex I: 2.11.4.2. The classification procedure for self-heating substances or mixtures 
need not be applied if the results of a screening test can be adequately correlated with the 
classification test and an appropriate safety margin is applied. Examples of screening tests 
are: 

(a)     The Grewer Oven test (VDI guideline 2263, part 1, 1990, Test methods for the De-
termination of the Safety Characteristics of Dusts) with an onset temperature 80 K above 
the reference temperature for a volume of 1 l; 

(b)     The Bulk Powder Screening Test (Gibson, N. Harper, D.J. Rogers, R. Evaluation of the 
fire and explosion risks in drying powders, Plant Operations Progress, 4 (3), 181-189, 
1985) with an onset temperature 60 K above the reference temperature for a volume of 1 l. 

Note:  Regarding  point  'a'  in  the  above  table,  VDI40  2263,  part  1  has  been  updated  to  a  new 
version: VDI 2263, part 1, 2022, Dust fires and dust explosions - Hazards - assessment - safety 
measures - Safety-related parameters of bulk goods. 

40 VDI: Verein Deutscher Ingenieure - Association of German Engineers 

 
 
 
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EU  test  method  A.16,  as  described  in  Regulation  (EC)  No  440/2008,  checks  for  self-heating 
properties.  However,  the  method  is  generally  inappropriate  for  a  sound  assessment  of  self-
heating, and the findings do not lead to a classification. Therefore, special care must be taken if 
results from EU test method A.16 are interpreted towards a CLP classification for self-heating 
substances  and  mixtures.  Even  if  a  temperature  rise  up  to  400  °C  due  to  self-heating  is  not 
observed, such behaviour cannot be interpreted as conclusive for “no classification”. 

In general, the phenomenon of self-heating applies only to solids. The surface of liquids is not 
large  enough for reaction with air and the test method is not applicable to liquids. Therefore, 
liquids are not classified as self-heating. However, if liquids are adsorbed on a large surface (e.g. 
on powder particles or a textile mesh), a self-heating hazard should be considered.  

Substances  or  mixtures  with  a  low  melting  point  (<  160  °C)  should  not  be  considered  for 
classification  as  self-heating  since  the  melting  process  is  endothermic  and  the  substance-air 
surface  is  drastically  reduced.  However,  this  criterion  is  only  applicable  if  the  substance  or 
mixture  is  completely  molten  up  to  this  temperature  (i.e.  the  test  basket  of  an  isothermal 
Grewer test at 160 °C as mentioned in UN-MTC section 3.12.4.2 a) or in any one of the UN N.4 
tests is empty after the test). Sublimation in the  same temperature  range is also effective in 
suppressing self-heating. However, if some material remains in the test basket in such a way 
that the temperature sensor as described in UN-MTC section 33.4.6.2 c) has lost contact, it may 
be  helpful  for  the  interpretation  of  the  findings  to  repeat  the  experiment  with  an  additional 
thermocouple in place. 

2.11.4.3.  Classification criteria 

A self-heating substance or mixture must be classified in one of the two categories for this class 
if, in a test performed in accordance with UN Test N.4 in Part III, section 33.4.6 of the UN-MTC, 
the result meets the criteria according to following table: 

Annex I: Table 2.11.1 

Criteria for self-heating substances and mixtures 

Category  Criteria 

1 

A positive result is obtained in a test using a 25 mm sample cube at 140 °C 

(a)  a positive result is obtained in a test using a 100 mm sample cube at 140 °C 
and a negative result is obtained in a test using a 25 mm cube sample at 
140 °C and the substance or mixture is to be packed in packages with a volume 
of more than 3 m3; or 

(b)  a positive result is obtained in a test using a 100 mm sample cube at 140 °C 
and a negative result is obtained in a test using a 25 mm cube sample at 
140 °C, a positive result is obtained in a test using a 100 mm cube sample at 
120 °C and the substance or mixture is to be packed in packages with a volume 
of more than 450 litres; or 

(c)  a positive result is obtained in a test using a 100 mm sample cube at 140 °C 
and a negative result is obtained in a test using a 25 mm cube sample at 140 
°C and a positive result is obtained in a test using a 100 mm cube sample at 
100 °C. 

2 

Note 

The test shall be performed on the substance or mixture in its physical form as presented. 
If, for example, for the purposes of supply or transport, the same chemical is to be presented 
in a physical form different from that which was tested and which is considered likely to 
materially alter its performance in a classification test, the substance shall also be tested in the 
new form. 

 
 
 
 
 
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2.11.2.3. Substances and mixtures with a temperature of spontaneous combustion higher than 
50 °C for a volume of 27 m³ shall not be classified as a self-heating substance or mixture. 

2.11.2.4. Substances and mixtures with a spontaneous ignition temperature higher than 50 °C 
for a volume of 450 litres shall not be assigned to Category 1 of this class. 

2.11.4.4.  Testing and evaluation of hazard information 

A self-heating substance or mixture must be classified in one of the two categories for this class 
using UN Test N.4 in Part III, section 33.4.6 of the UN-MTC. 

2.11.4.4.1.  General remarks 

If  self-heating  behaviour  cannot  be  ruled  out  by  a  screening  test,  further  testing  becomes 
necessary. UN Test N.4 as described in the latest version of the UN-MTC should be used. 

Explosive  substances and mixtures should not be tested according to this method. For safety 
reasons,  it  is  necessary  to  first  test  for  explosive  and  self-reactive  properties  and  to  rule  out 
pyrophoric  behaviour  before  performing  this  test.  The  oven  should  be  equipped  with  an 
appropriate  pressure-release  device  in  case  an  energetic  decomposition  is  triggered  by  a 
temperature  rise.  For  samples  containing  flammable  solvents  explosion  protection  measures 
have to be taken. 

It  is  of  utmost  importance  that  in  compliance  with  Articles  5  and  6  of  CLP  authentic  and 
representative material in the correct form and physical state is used for testing. 

The tests for self-heating properties may be performed in any order. It is suggested to start with 
the 25 mm  sample  cube at 140 °C. If a positive result is  obtained, the  substance  or mixture 
must be classified as a self-heating substance or mixture, category 1, and no further testing is 
necessary. 

2.11.4.4.2.  Sample preparation 

The sample (powder or granular) in its commercial form should be used and should not be milled 
or  ground.  It  should  be  filled  to  the  brim  of  the  sample  container  and  the  container  tapped 
several times. If the sample settles, more is added. If the sample is heaped it should be levelled 
to  the  brim.  The  sample  container  is  placed  in  the  oven  as  described  in  the  UN-MTC,  section 
33.4.6.3. 

2.11.4.4.3.  Test conduction, criteria and evaluation 

A positive result is obtained if spontaneous ignition occurs or if the temperature of the sample 
exceeds  the  oven  temperature  by  60 °C.  The  testing  time  is  24  hours.  The  time  count  starts 
when the temperature in the centre of the sample has reached a value of 2 °C below the oven 
temperature. This is especially important when the sample contains solvents which evaporate 
under the test conditions or when larger test volumes are used for extrapolation purposes (see 
below). 

Before starting UN Test N.4, the decomposition behaviour of the sample should be known. In 
general, it is sufficient to perform a screening Differential Scanning Calorimetry measurement; 
see  UN-MTC  section  20.3.3.3.  Test  data  needs  to  be  interpreted  cautiously  if  exothermic 
decomposition  may  occur  at  the  test  temperatures.  In  such  cases,  a  test  under  an  inert 
atmosphere  (i.e.  nitrogen)  should  be  run  to  determine  the  temperature  rise  due  to 
decomposition. Thorough flushing with the chosen inert gas is essential in such cases since air 
may  be  retained  between  the  crystals  of  the  sample  in  the  container.  If  endothermic 
decomposition  occurs  during  testing  (for  example,  release  of  flammable  or  toxic  gases)  the 
criterion of a 60 °C temperature rise according to UN-MTC section 33.4.6.3 may not be fulfilled 
because temperature increase is hindered by the endothermic decomposition. However, if such 
a reaction may be triggered by self-heating the criterion for classification should be considered 

 
 
 
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as  fulfilled.  An  additional  thermogravimetric  measurement  is  advisable  for  assessment  under 
these circumstances. 

2.11.4.5.  Decision logic 

The following decision logic for self-heating substances and mixtures is applicable according to 
CLP.  

NOTE: The person responsible for the classification of self-heating substances and mixtures 
should be experienced in this field and be familiar with the criteria for classification. 

 
 
 
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Annex I: Figure 2.11.1. 

Self-heating substances and mixtures 

SUBSTANCE/MIXTURE 

Does it undergo dangerous self-heating when 
tested in a 100 mm sample cube at 140 °C? 

NO 

NOT CLASSIFIED 

YES 

Does it undergo dangerous self-heating when 
tested in a 25 mm sample cube at 140 °C? 

NO 

Is it packaged in more than 3 m3? 

NO 

YES 

YES 

Category 1 

Danger 

Category 2 

Warning 

Does it undergo dangerous self-heating when 
tested in a 100 mm sample cube at 120 °C? 

NO 

NOT CLASSIFIED 

YES 

Category 2 

Is it packaged in more than 450 litres volume? 

YES 

NO 

Warning 

Does it undergo dangerous self-heating when 
tested in a 100 mm sample cube at 100 °C? 

YES 

Category 2 

NO 

NOT CLASSIFIED 

Warning 

2.11.4.6.  Exemption 

The following exemptions apply (see section 2.11.4.3): 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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•  Substances  and  mixtures  with  a  temperature  of  spontaneous  combustion  higher  than 
50 °C for a volume of 27 m³ shall not be classified as a self-heating substance or mixture 
(CLP, 2.11.2.4). 

•  Substances and mixtures with a spontaneous ignition temperature higher than 50 °C for 

a volume of 450 litres must not be assigned to category 1 of this class. 

However, the UN-MTC does not provide any guidance on how these values should be determined. 
According to Grewer (Grewer, 1994), plotting the logarithm of the volume to surface ratio (log 
(V/A))  versus  the  reciprocal  temperature  gives  good  results  without  knowledge  of  the  Frank-
Kamenetskii (Frank-Kamenetskii, 1969) shape factor. This method had first been suggested by 
Leuschke  (Leuschke,  1976  and  1981)  as  an  empirical  alternative  to  the  Frank-Kamenetskii 
approach. 

The critical temperature for a volume of 450 l or 27 m³ can be found by extrapolation of the 
critical temperature in a log (V/A) vs. 1/T plot (see Figure 2.8): 

Figure 2.8 Extrapolation towards large volumes  

A standardised procedure can be found in BS EN 15188:2020 “Determination of the spontaneous 
ignition behaviour of dust accumulations”. 

The test setup is essentially the same as in UN Test N.4 of the UN-MTC but now the sample size 
and possibly the shape are systematically varied. The criteria in section 2.11.4.3 apply as well. 

The critical temperature must be determined over a range of at least four different volumes and 
with a volume not smaller than 16 ml. If possible, larger  volumes  should be also tested. The 
borderline temperature should be determined as precisely as possible. For small volumes (< 1 
litre), the temperature rise due to self-heating may be considerably less than 60 °C; in this case 
a noticeable temperature rise is interpreted as a positive result. 

A conservative approach is required for the evaluation. The uncertainty of measurement must 
be taken into account. The extrapolation must be based on a linear regression of the negative 
and positive borderline data sets in the log (V/A) vs. 1/T diagram. An exemption may be claimed 

400 mL100 L50607080901001201401601802002202401,6 L110 mL16 mL1 m310 m327 m3-3,0-2,8-2,6-2,4-2,2-2,0-1,8-1,6-1,4-1,2-1,0-0,8-0,6-0,40,00190,00200,00210,00220,00230,00240,00250,00260,00270,00280,00290,00300,0031log(V/A) in mTemperature in °CSample volumereciprocal abs. Temperature in 1/K    positive result    negative resultNote: sample gave positiveresult at 140 °C / 1 literLinear regression linesExtrapolation to 27 m³ 
 
 
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if the more conservative endpoint for the particular volume is well beyond 50 °C (i.e. 55 °C or 
higher). 

It  should  be  noted  that  the  slope  of  the  line  in  the  1/T  vs.  volume  diagram  depends  on  the 
individual activation energy of the substance or mixture, so it may vary within certain limits. It 
must be born in mind that this test regime has been developed to facilitate classification and 
that it may not suffice to solve safety issues in storage.  

A significant increase in the accuracy of the extrapolation can be achieved by conducting tests 
on a semi-industrial scale. Experiments up to a volume of 1 m³ are presented in Martin Schmidt 
et al. (2022). For all materials investigated so far, the critical temperatures of the 1 m³ sample 
were higher than predicted by the extrapolation of laboratory tests according to Leuschke (1976 
and 1981). 

In Martin Schmidt et al. (2022), a further screening method based on the direct measurement 
of the heat flows at process temperatures (microcalorimetric low-temperature measurements) 
is also introduced. 

2.11.5.  Hazard communication for self-heating substances or mixtures 

2.11.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

Annex I: Table 2.11.2 

Label elements for self-heating substances and mixtures 

Classification 

Category 1 

Category 2 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

H251: Self-heating; may 
catch fire 

H252: Self-heating in large 
quantities; may catch fire 

Precautionary Statement 
Prevention 

Precautionary Statement Response 

Precautionary Statement Storage 

Precautionary Statement Disposal 

P235 

P280 

P407 

P413 

P420 

P235 

P280 

P407 

P413 

P420 

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2.11.6.  Relation to transport classification 

Division 4.2 – substances and mixtures liable to spontaneous combustion – within Class 4 of the 
UN RTDG Model Regulations comprises the following entries: 

a.  pyrophoric substances and mixtures; 

b.  self-heating substances and mixtures. 

Whereas pyrophoric substances and mixtures in the modal transport regulations (ADR, RID, ADN 
and IMDG Code, ICAO TI) are assigned to packing group I, self-heating substances and mixtures 
are assigned to packing groups II and III. In cases where a substance or mixture is classified in 
Division 4.2, packing group II or III, the translation into the CLP system is straightforward. 

It should be kept in mind that transport classification is based on prioritisation of hazards (see 
the UN RTDG Model Regulations, section 2.0.3) and that self-heating substances and mixtures 
have  a  relatively  low  rank  in  the  precedence  of  hazards.  Therefore,  the  translation  from  the 
modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) to CLP should be only 
done  if  a  transport  classification  as  self-heating  is  explicitly  available.  The  conclusion  that  a 
substance  or  mixture  not  classified  as  self-heating  for  transport  should  not  be  classified  as  a 
self-heating substance or mixture according to CLP is, in general, not correct. See  Annex I for 
additional information on transport classification in relation to CLP classification. 

2.11.7.  Examples of classification for self-heating substances or mixtures 

2.11.7.1.  Example of substances and mixtures fulfilling the classification 
criteria 

An example for the classification procedure is  shown in the following  diagrams  obtained  from 
performing the UN N.4 test according to the UN-MTC. 

Figure 2.9 Results of UN N.4 Test according to the UN-MTC 

 
 
 
 
 
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121 

The temperature rises in the 25 mm cube from 140 °C to 146 °C (first diagram) and in the 100 
mm cube from 100 °C  to 118 °C (last diagram). At 120 °C and 140 °C in the 100 cube, the 
temperature increase is far beyond 60 °C. 

For a substance or mixture packaged in a volume of 1000 litres, the classification comes to the 
following result. 

Figure 2.10 Results of UN N.4 Test according to the UN-MTC 

 
 
 
 
 
 
 
 
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2.11.7.2.  Example of substances and mixtures not fulfilling the 
classification criteria 

In general, liquids show no self-heating behaviour unless adsorbed on a large surface. 

Scientific background 

A  basic  model  for  the  thermal  explosion  of  solids  was  first  developed  by  Frank-Kamenetskii 
(Frank-Kamenetskii,  1969).  It  is  based  on  the  assumption  that  only  the  heat  loss  by  thermal 
conduction  is  relevant  for  the  phenomenon.  In  this  case,  the  critical  criterion  for  a  thermal 
runaway  reaction  can  be  described  as  a  linear  relationship  between  the  reciprocal  absolute 
temperature and the logarithm of volume. 

The classification scheme of the UN for self-heating substances and mixtures is based on charcoal 
as a reference system. The critical temperature for a 1 litre cube of charcoal is 140 °C and for a 
cube of 27 m³ 50 °C. When a parallel line is drawn in the 1/T vs. logarithm of volume diagram 

from the reference points 1 litre / 120 °C and 1 litre / 100 °C, the corresponding volumes for a 
critical temperature of 50 °C are found to be 3 m³ and 450 litre, respectively (see ). The black 
dotted line in  separates category 1 from category 2. For examples of results obtained in Test 
N.4 see section 33.3.4.6.5 of UN-MTC. 

Figure 2.11 Volume dependency of the critical temperature for charcoal 

2.11.8.  References 

Grewer, T. (1994). Thermal hazards of chemical reactions, Elsevier. 

Frank-Kamenetskii, D.A. (1969).  Diffusion and heat transfer in chemical kinetics, 2nd edition, 
Plenum Press, New York, London. 

Leuschke G. (1976). Self-Ignition of Powdered Materials, VFBD 5th International Fire Protection 
Seminar.  

Leuschke,  G.  (1981).  Experimental  investigations  on  self-ignition  of  dust  deposits  in  hot 
environments,  Runaway  Reactions,  Unstable  Products  and  Combustible  Powders,  IChemE 
Symposium Series 68. 

0,0020,00220,00240,00260,00280,0030,00320,0010,010,1110100100010000100000Temperature (°C)5060708090100120140160180200220Volume (liter)recipr.Temp.Charcoalreferenceline(UN Manual T + C)Not self-heatingExemption< 3 m³Exemption< 450 ltrCat. 1Cat. 2YellowdotssymbolizeUN Manual test pointsGrewer test 
 
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123 

Martin Schmidt, Marcus Gödde, Steffen Salg, René Erdt (2022). Self-ignition Behaviour of Bulk 
Materials:  How  Reliable  is  the  Extrapolation  of  Laboratory  Tests?,  Chemical  Engineering 
Transactions, Vol. 90, 289-294, DOI: 10.3303/CET2290049. 

2.12. SUBSTANCES OR MIXTURES WHICH, IN CONTACT WITH WATER, 
EMIT FLAMMABLE GASES 

2.12.1.  Introduction 

The criteria for ‘Substances and mixtures which, in contact with water, emit flammable gases’ 
are found in CLP Annex I, section 2.12 and are identical to those in chapter 2.12 of GHS18. 

Depending on the chemical structure and/or the physical state (e.g. particle size) substances or 
mixtures  may  be  able  to  react  with  water  (even  damp  /  air  humidity)  under  normal  ambient 
temperature  conditions.  Sometimes  this  reaction  can  be  violent  and/or  with  significant 
generation of heat. Where flammable gases evolve, this reaction may become very dangerous 
during use. In addition, it is important to know whether a substance or mixture emits flammable 
gases after contact with water because special precautions are necessary especially with regard 
to explosion protection. 

2.12.2.  Definitions and general considerations for classification of substances 

or mixtures which, in contact with water, emits flammable gases 

The following definition is given in CLP for substances and mixtures which, in contact with water, 
emit flammable gases (CLP Annex I, section 2.12). 

Annex I: 2.12.1. Substances or mixtures which, in contact with water, emit flammable gases 
means solid or liquid substances or mixtures which, by interaction with water, are liable to 
become spontaneously flammable or to give off flammable gases in dangerous quantities. 

2.12.3.  Relation to other physical hazards 

Gases exhibiting hazards other than flammability may be released by substances in contact with 
water. Some examples are demonstrated in the following table. 

Table 2.2 Examples of hazards, depending on the property of the emitted gas, when 
substances and mixtures are in contact with water 

Type of 
emitted gas  

Gas  
(in general) 

Example of hazards other than flammability  

CLP Reference 

•  Heating up of the substance 

•  Splashing of the substance and for example, 

contact with skin etc. or additional risk during 
fire fighting 

Annex II, section 1.1.3: 
Supplemental hazard 
information: 

EUH014* 

Flammable gas 

• 

• 

• 

Pressure rise and bursting of e.g. the 
packaging, tank 

Ignition  

Flash of fire 

Toxic gas 

•  Damage to health: intoxication (acute) 

Annex I, section 2.12: 
H260/H261 

Annex II, section1.2.1: 
Supplemental hazard 
information: 

 
 
 
 
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EUH029 

* For supplemental hazard information: see section 2.12.5.2 

If the chemical identity of the emitted gas is unknown, the gas must be tested for flammability 
(unless it ignites spontaneously). Pyrophoric liquids and pyrophoric solids have to be considered 
for classification in this hazard class as well and data about pyrophoric properties are needed 
prior to testing for this hazard class. 

2.12.4.  Classification of substances and mixtures which, in contact with 

water, emits flammable gases 

2.12.4.1. 

Identification of hazard information 

For the classification of substances and mixtures which, in contact with water, emit flammable 
gases the following data are needed, if applicable: 

• 

chemical structure; 

•  water solubility; 

• 

chemical identity and flammability of the emitted gas; 

•  pyrophoric properties of the tested substance or mixture; 

•  particle size in case of solids; 

• 

friability in case of solids;  

•  hazard properties in general; 

• 

information concerning the experience in production or handling.  

See also IR & CSA, Chapter R.7a: Endpoint specific guidance, section R.7.1.7 (Water solubility) 
and R.7.1.14 (Granulometry). 

Information  about  the  chemical  structure  is  used  to  check  whether  the  substance  or  mixture 
contains metals and/or metalloids. 

Many different types of chemicals may belong to the hazard class of substances and mixtures 
which, in contact with water, emit flammable gases, for example, alkali metals, alkyl aluminium 
derivatives, alkyl metals, metal hydrides, metal phosphides, certain metal powders. An extensive 
list can be found in Bretherick’s Handbook of Reactive Chemical Hazards (Urben, 2007). 

The water solubility is used to decide whether the substance or mixture is  soluble in water to 
form a stable mixture. This may also be decided based on information concerning experience in 
handling or use, e.g. the substance or mixture is manufactured with water or washed with water 
(see section 2.12.4.4.1). 

The chemical identity of the emitted gas is used to decide whether the evolved gas is flammable 
or  not.  If  the  chemical  identity  of  the  emitted  gas  is  unknown,  the  gas  must  be  tested  for 
flammability (see section 2.2). 

In case of pyrophoric substances and mixtures the UN Test N.5 of the UN-MTC, Part III, section 
33.5.4.  must  be  executed  under  nitrogen  atmosphere.  Therefore,  data  about  pyrophoric 
properties are needed prior to testing. 

The  melting  point,  boiling  point  and  information  about  viscosity  are  necessary  to  identify  the 
physical state of the substance or mixture. See also IR & CSA, Chapter R.7a: Endpoint specific 
guidance, sections R.7.1.2 (Melting point/freezing point), R.7.1.3 (Boiling point), and R.7.1.18 
(Viscosity). Even though the UN Test N.5 can be applied to both, solids and liquids, these data 
are necessary to decide whether information concerning the friability (for solids) in accordance 
with the test method is necessary.  

 
 
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The particle size and the friability of a solid substance or mixture are crucial parameters for the 
classification of substances and mixtures which, in contact with water, emit flammable gases. 
These  parameters  have  a  significant  effect  on  the  test  result.  Thus,  specific  requirements 
regarding the particle size and the friability are prescribed in the UN Test N.5. For further details 
regarding the test procedure see section 2.12.4.4.1. 

The references in section 2.12.8 provide good quality data on physical hazards. 

2.12.4.2.  Screening procedures and waiving of testing 

For the majority of substances and mixtures, flammability as a result of contact with water is 
not a typical property and testing can be waived based on a consideration of the structure and 
experiences in handling and use. 

Annex I: 2.12.4.1. The classification procedure for this class need not be applied if: 

a) the chemical structure of the substance or mixture does not contain metals or 

metalloids; or 

b) experience in handling and use shows that the substance or mixture does not react with 

water, e.g. the substance is manufactured with water or washed with water; or 

c) the substance or mixture is known to be soluble in water to form a stable mixture. 

2.12.4.3.  Classification criteria 

Annex I: Table 2.12.1 

Criteria for substances or mixtures which in contact with water emit flammable gas 

Category  Criteria 

Any substance or mixture which reacts vigorously with water at ambient 
temperatures and demonstrates generally a tendency for the gas produced to 
ignite spontaneously, or which reacts readily with water at ambient temperatures 
such that the rate of evolution of flammable gas is equal to or greater than 10 
litres per kilogram of substance over any one minute. 

Any substance or mixture which reacts readily with water at ambient temperatures 
such that the maximum rate of evolution of flammable gas is equal to or greater 
than 20 litres per kilogram of substance per hour, and which does not meet the 
criteria for Category 1. 

Any substance or mixture which reacts slowly with water at ambient temperatures 
such that the maximum rate of evolution of flammable gas is equal to or greater 
than 1 litre per kilogram of substance per hour, and which does not meet the 
criteria for Categories 1 and 2. 

1 

2 

3 

Note: 

The test shall be performed on the substance or mixture in its physical form as presented. If 
for example, for the purposes of supply or transport, the same chemical is to be presented in 
a physical form different from that which was tested and which is considered likely to 
materially alter its performance in a classification test, the substance must also be tested in 
the new form. 

 
 
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2.12.2.2. A substance or mixture shall be classified as a substance or mixture which in 
contact with water emits flammable gases if spontaneous ignition takes place in any step of 
the test procedure. 

2.12.4.4.  Testing and evaluation of hazard information 

2.12.4.4.1.  Testing procedure 

Care must be taken during testing as the emitted gas might be toxic or corrosive. 

The testing procedure for substances and mixtures which in contact with water emit flammable 
gases  is  sensitive  to  a  number  of  influencing  factors  and  therefore  must  be  carried  out  by 
experienced personnel. Some of these factors are described in the following: 

1.  Apparatus / measuring technique 

In UN Test N.5 no special laboratory apparatus / measuring technique to determine the rate of 
gas evolution is required and no reference material is prescribed. As demonstrated in the past 
by  a  round  robin  test  (Kunath,  K.  et  al.  2011),  the  gas  evolution  rate  measured  by  different 
apparatuses may vary widely. Therefore, to avoid measuring and classification errors adequate 
quality control measures are necessary to validate the results and should be noted in the test 
report. 

2.  Particle size and/or friability 

The particle size of a solid has a significant effect on the test result. Therefore, if for solids the 
percentage of powder with a particle size of less than 500 µm constitutes more than 1 % of the 
total mass, or if the substance or mixture is friable, then the complete sample must be ground 
to a powder before testing to account for a possible reduction in particle size during handling 
and transport.  

In certain cases, grinding may not be applicable and/or the sample cannot be ground completely 
to a particle size of less than 500 µm (e.g. metal granules). 

Information on these pre-treatments and the respective procedures, the particle  size and the 
friability have to be provided in the test report. 

3.  Atmospheric parameters  

Variations of the atmospheric parameters (mainly air pressure and temperature) during the test 
have a considerable influence on the test result. Therefore, the substance or mixture must be 
tested at 20 °C, i.e. make sure that the test apparatus is acclimatised to 20 °C. 

However, it is difficult to regulate and stabilise the air pressure during the testing. To characterise 
this  influencing  factor  and  to  avoid  false  positive  results,  an  additional  ‘blank  test’  is  highly 
recommended. The results of the blank test should be noted in the test report. 

4.  Test with demineralised (distilled) water  

The UN Test N.5 is performed with demineralised (distilled) water. In practice, contact with water 
can be to water in the liquid state (fresh water, sea water) or humid air, respectively. Note that 
the reactivity and therefore the gas evolution rate observed in practice may differ from the gas 
evolution  rate  value  measured  using  demineralised  water.  This  should  be  taken  into  account 
when handling substances and mixtures which in contact with water emit flammable gases. 

5.  Stirring procedures during the test 

Stirring of the sample or water mixture during the test may have a considerable effect on the 
test result (e.g. significant increase or decrease of the gas evolution rate). Therefore, the sample 
or  water  mixture  should  not  be  stirred  continuously  during  the  test,  e.g.  by  an  automatic 
magnetic  stirrer,  even  if  the  test  sample  has  hydrophobic  properties  and  moistening  of  the 
sample becomes impossible (see Kunath K. et al., 2011). 

6.  Spontaneous ignition 

 
 
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Spontaneous ignition of the evolved gas without contact with an additional ignition source, i.e. 
without  the  flame  of  the  gas  burner  results  in  classification  as  category  1.  This  does  not 
necessarily mean that the evolved gas is pyrophoric but often the heat of reaction is sufficient 
to ignite the evolved gas (e.g. the hydrogen evolved when sodium reacts with water). 

2.12.4.4.2.  Evaluation of hazard information 

To accurately interpret the test results the evaluating person must have sufficient experience in 
the application of the test methods and in the disturbing / influencing factors as described above. 

The evaluation of data comprises two steps: 

•  evaluation of all available data; and 

• 

identification of the study or studies giving rise to the highest concern (key studies). 

The  criteria  for  assignment  to  categories  2  or  3  are  gas  evolution  rates  of  20  and  1  litre  per 
kilogram of substance or mixture per hour, respectively, but for category 1 the relevant criterion 
is 10 litres per kilogram of substance or mixture over any one minute period (if the gas does not 
ignite spontaneously). This has to be considered while testing and for correct evaluation of the 
test results. 

The  assignment  to  the  respective  hazard  class/category  will  further  determine  the  technical 
means  to  be  taken  to  avoid  dangerous  events  which,  in  combination  with  other  safety 
characteristics such as i) explosion limits, ii) flash points (applicable only for liquids) or iii) self-
ignition temperature, can lead to clear restrictions in the conditions of use. 

2.12.4.5.  Decision logic 

Classification of substances and mixtures which, in contact with water, emit flammable gases is 
done according to decision logic 2.12.4.1 as included in GHS. 

NOTE: The person responsible for the classification of substances and mixtures which, in 
contact with water, emit flammable gases should be experienced in this field and be familiar 
with the criteria for classification. 

 
 
 
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Figure 2.12 Decision logic for substances and mixtures which, in contact with water, emit 
flammable gases (Decision logic 2.12 of GHS) 

Substance/mixture 

In contact with water, does it react slowly at ambient temperatures such 
that the maximum rate of evolution of flammable gas is > 1 litre per kg 
of substance per hour? 

No 

Not classified  

Yes 

In contact with water, does the substance react vigorously with water at 
ambient temperatures and demonstrate generally a tendency for the gas 
produced to ignite spontaneously, or does it react readily with water at 
ambient temperatures such that the rate of evolution of flammable gas is 
≥ 10 litres per kg of substance over any one minute? 

Yes 

No 

In contact with water, does it react readily with water at ambient 
temperatures such that the maximum rate of evolution of flammable 
gas is ≥ 20 litres per kg of substance per hour? 

Yes 

No 

Category 1 

Danger 

Category 2 

Danger 

Category 3 

Warning 

 
 
 
 
 
 
 
 
 
 
 
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2.12.5.  Hazard communication for substances or mixtures which, in contact 

with water, emits flammable gases 

2.12.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

Annex I: Table 2.12.2 

Label elements for substances or mixtures which in contact with water emit 
flammable gases 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Hazard Statement 

H260: 

Danger 

H261: 

Warning 

H261: 

In contact with water 
releases flammable 
gases which may 
ignite spontaneously 

In contact with 
water releases 
flammable gases 

In contact with 
water releases 
flammable gases 

Precautionary 
Statement 
Prevention 

P223 

P223 

P231 + P232 

P231 + P232 

P231 + P232 

P280 

P280 

P280 

Precautionary 
Statement Response 

P302 + P335 + P334 

P370 + P378 

P302 + P335 + 
P334 

P370 + P378 

P370 + P378 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

P402 + P404 

P402 + P404 

P402 + P404 

P501 

P501 

P501 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.12.5.2.  Additional labelling provisions 

Annex  II  to  CLP  provides  the  following  additional  labelling  provisions  for  water-reactive 
substances and mixtures. These statements must be assigned in accordance with CLP, Article 
25(1), to substances and mixtures classified for physical, health or environmental hazards. There 
are no criteria or test methods provided for these EUH statements. 

 
 
 
 
 
 
 
 
 
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Annex II: 1.1.1.     EUH014 – 'Reacts violently with water' 

For substances and mixtures which react violently with water, such as acetyl chloride, alkali 
metals, titanium tetrachloride. 

Annex II: 1.2.1.     EUH029 - 'Contact with water liberates toxic gas' 

For substances and mixtures which in contact with water or damp air, evolve gases classified 
for acute toxicity in category 1, 2 or 3 in potentially dangerous amounts, such as aluminium 
phosphide, phosphorus pentasulphide. 

2.12.6.  Relation to transport classification 

Division 4.3 within Class 4 of the UN RTDG Model Regulations covers substances and mixtures 
which in contact with water emit flammable gasses. Substances and mixtures which are classified 
and/or  labelled  in  Division  4.3  in  the  modal  transport  regulations  (ADR,  RID,  ADN  and  IMDG 
Code,  ICAO  TI)  are  classified  as  substances  and  mixtures  which,  in  contact  with  water,  emit 
flammable gases under CLP. See Annex I for additional information on transport classification in 
relation to CLP classification. 

2.12.7.  Example of classification for substances or mixtures which, in contact 

with water, emits flammable gases 

2.12.7.1.  Example of substances and mixtures fulfilling the classification 
criteria 

2.12.7.1.1.  Example 1 

SUBSTANCE FULFILLING THE CRITERIA FOR CLP CLASSIFICATION 

Substance: 

Magnesium alkyls (Index No. 012-003-00-4) 

Chemical structure: 

Flammable gas: 

R2Mg  

Hydrogen 

Gas evolution rate: 

Not applicable 

Spontaneous ignition: 

Not possible due to the nitrogen atmosphere during the 
UN Test N.5  

Transport classification: 

- 

Reference: 

Former Annex I to DSD and Annex VI to CLP 

 CLP Classification: 

Water-react. 1; H260 

Pyr. Sol. 1; H250 

Supplemental Hazard Information: 

EUH014 

 
 
 
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2.12.7.2.  Example of substances and mixtures not fulfilling the 
classification criteria 

2.12.7.2.1.  Example 2 

SUBSTANCE NOT FULFILLING THE CRITERIA FOR CLP CLASSIFICATION 

Substance 

Manganese ethylene bis (dithiocarbamate) complex with 
zinc salt 88% (Mancozeb) 

Gas evolution rate: 

0 litres per kilogram of substance per hour. 

Spontaneous ignition: 

Not applicable 

Transport classification: 

Not Class 4.3 

Reference: 

UN Test N.5, UN-MTC section 33.5.4.5 

 CLP Classification: 

Not classified as substance which, in contact with 
water, emit flammable gases 

2.12.8.  References 

Haynes, W. M. et al. (2012) CRC Handbook of Chemistry and Physics 93rd Edition. CRC Press, 
Taylor and Francis, Boca Raton, FL 

GESTIS-database on hazardous substances: 
https://www.dguv.de/ifa/gestis/gestis-stoffdatenbank/index-2.jsp 

Janès,  A.,  Marlair,  G.,  Carson,  D.,  Chaineaux,  J.  (2012)  Towards  the  improvement  of  UN  N.5 
test method for the characterization of substances which in contact with water emit flammable 
gases,  Journal  of  Loss  Prevention  in  the  Process  Industries,  Volume  25,  Issue  3,  524-534, 
https://www.sciencedirect.com/science/article/pii/S0950423011002166 

Kunath, K., Lüth, P., Uhlig, S. (2011). Interlaboratory test on the method UN Test N.5 / EC A.12 
“Substances  which,  in  contact  with  water,  emit  flammable  gases”  2007.  Short  report.  BAM 
Bundesanstalt 
für  Materialforschung  und  –prüfung.  Berlin.  ISBN  978-3-9814634-1-5. 
http://www.bam.de/de/service/publikationen/publikationen_medien/short__report_rv_un_n_5
.pdf 

O'Neil, Maryadele J. et al. (2016, 2012) The Merck Index - An Encyclopaedia of Chemicals, Drugs, 
and Biologicals (14th Edition – Version 14.9). Merck Sharp & Dohme Corp., a subsidiary of Merck 
& Co., Inc. 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier

 
 
 
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2.13. OXIDISING LIQUIDS 

2.13.1.  Introduction 

The  criteria  for  ‘Oxidising  liquids’  are  found  in  CLP  Annex  I,  section  2.13  and  are  identical  to 
those in chapter 2.13 of GHS18. 

The  hazard  class  oxidising  liquids  comprises  liquid  substances  and  mixtures  whose  hazard  is 
characterised  by  the  fact  that,  in  contact  with  other  materials,  they  are  able  to  cause  or 
contribute to the combustion of those materials. The other materials do not necessarily have to 
belong to a certain hazard class to be able to be affected by the presence of oxidising substances 
or mixtures. This is for example the case when a solid material (e.g. wood) is soaked with an 
oxidising liquid. 

Certain combinations of combustible materials and oxidising substances or mixtures may even 
result in spontaneous combustion, thermal instability or form an explosive mixture. 

Although  widely  known  as  oxidising  materials,  their  hazard  and  behaviour  might  be  better 
understood by considering them to be fire enhancing substances or mixtures. 

Apart from the combustion hazard, the production of toxic and/or irritating fumes may cause an 
additional  hazard.  For  example,  when  nitrates  are  involved  in  a  fire,  nitrous  fumes  may  be 
formed. 

The testing procedure and criteria for oxidising substances or mixtures are not appropriate for 
ammonium nitrate compounds or solutions, ammonium nitrate-based fertilisers, and ammonium 
nitrate  emulsions,  suspensions  or  gels  due  to  their  complex  hazard  profiles.  Therefore,  for 
classification and labelling of substances or mixtures containing ammonium nitrate, experience 
should  be  used  and  expert  judgement  should  be  sought.  For  the  classification  procedures  for 
intermediates for blasting explosives, such as ammonium nitrate emulsions, suspensions or gels, 
see section 2.1. 

Annex I: 2.13.4.3  

In the event of divergence between test results and known experience in the handling and 
use of substances or mixtures which shows them to be oxidising, judgments based on 
known experience shall take precedence over test results. 

2.13.2.  Definitions and general considerations for classification of oxidising 

liquids 

The CLP text comprises the following definition for oxidising liquids. 

Annex I: 2.13.1.     Definition 

Oxidising liquid means a liquid substance or mixture which, while in itself not necessarily 
combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of 
other material. 

2.13.3.  Relation to other physical hazards 

Oxidising  liquids  that  are  mixed  with  combustible  materials  or  reducing  agents  may  have 
explosive properties and should be considered for  classification in the hazard class  explosives 
(including the applicable screening procedures), see section  2.1 or as self-reactive substances 
and mixtures, see CLP Annex I, section 2.8.2.1(b) and section 2.8. 

 
 
 
 
 
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The classification procedure and criteria for  oxidising substances  or mixtures is not applicable 
for organic peroxides. The majority of the organic peroxides do not possess oxidising properties; 
their main hazards are reactivity and flammability. Under CLP, organic peroxides are comprised 
in a separate hazard class (CLP Annex I, section 2.15) and they must not be considered according 
to the procedures described for oxidising liquids.  

Inorganic oxidising liquids are not flammable and therefore do not have to be subjected to the 
classification  procedures  for  the  hazard  classes  flammable  liquids  or  pyrophoric  liquids.  Also, 
other liquids that are classified as oxidising liquids are normally not flammable, although a few 
exemptions may exist. Expert judgement should be sought in case of doubt. 

2.13.4.  Classification of substances and mixtures as oxidising liquids 

2.13.4.1. 

Identification of hazard information 

Oxidising liquids may cause, or  contribute to,  the combustion  of other material. Although the 
definition states that they generally do this by yielding oxygen, halogens can behave in a similar 
way.  Therefore, any  substance  or mixture  containing oxygen and/or  halogen atoms  should in 
principle  be  considered  for  inclusion  into  the  hazard  class  oxidising  liquids.  This  does  not 
necessarily  mean  that  every  substance  or  mixture  containing  oxygen  and/or  halogen  atoms 
should be subjected to  the full testing procedure. For example, appropriate testing  should be 
considered when the screening criteria are not met. 

2.13.4.2.  Screening procedures and waiving of testing 

Liquids that are classified as explosives should not be subjected to the testing procedures for 
oxidising liquids. 

Organic  peroxides  should  be  considered  for  classification  within  the  hazard  class  organic 
peroxides, see section 2.15. For exceptional cases, in particular low concentrated peroxyacetic 
acid formulations see 2nd paragraph in section 2.15.6. 

Before  submitting  a  substance  or  a  mixture  to  the  full  test  procedure,  an  evaluation  of  its 
chemical  structure  may  be  very  useful  as  it  may  prevent  unnecessary  testing.  The  person 
applying this procedure should have sufficient experience in testing and in theoretical evaluation 
of  hazardous  substances  and  mixtures.  Some  substances  may  react  exothermally  with  the 
hydroxy groups in the cellulose molecule without affecting its polymeric structure. This reaction 
occurs spontaneously upon mixing and should not be interpreted as an oxidation. Substances 
known for such false positive behaviour are isocyanates and acid halides. Further, the following 
text provides a guideline for the theoretical evaluation of potential oxidising properties on the 
basis of its composition and chemical structure. In case of doubt, the full test must be performed. 

The CLP text comprises the following screening considerations: 

Annex I: 2.13.4.1. 

For organic substances or mixtures the classification procedure for this hazard class need not 
to be applied if: 

(a) 

the substance or mixture does not contain oxygen, fluorine or chlorine; or 

(b) 

the substance or mixture contains oxygen, fluorine or chlorine and these elements are 
chemically bonded only to carbon or hydrogen. 

2.13.4.2. 

For inorganic substances or mixtures, the classification procedure for this hazard class need 
not be applied if they do not contain oxygen or halogen. 

On the basis of this theoretical evaluation only a distinction can be made between ‘potentially 
oxidising’ (i.e. further testing required) and ‘non-oxidising’ (i.e. no further testing for this hazard 

 
 
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class required). It is not possible to assign a hazard category on basis of a theoretical evaluation. 
Even  though  for  ‘potentially  oxidising’  substances  classification  cannot  be  excluded  based  on 
theoretical evaluation, in some cases it might not be necessary to test a substance or mixture. 
However, this decision requires expert judgement. 

Any substance or mixture that complies with the above waiving criteria can be safely regarded 
to have no oxidising properties and, hence, does not to be tested and should not be regarded as 
an  oxidising  liquid.  However,  such  a  substance  or  mixture  may  still  possess  other  hazardous 
properties that require classification into another hazard class.  

In case a mixture of an oxidising substance and a non-hazardous inert substance is offered for 
classification, the following should be taken into account: 

•  By  definition  an  inert  material  does  not  contribute  to  the  oxidising  capability  of  the 
oxidising substance. Hence, the mixture can never be classified into a more severe hazard 
category. 

• 

If an oxidising substance is mixed with an inert material, the oxidising capability of the 
mixture does not linearly decrease with decreasing content of oxidising substance. The 
relationship is more or less logarithmic and depends on the characteristics of the oxidising 
substance. For instance, a mixture containing 50 % of a strong oxidiser and 50 % of an 
inert  material  may  retain  90  %  of  the  oxidising  capability  of  the  original  oxidising 
component.  Non-testing  classification  of  mixtures  based  solely  on  test  data  for  the 
original  oxidising  substance  should  therefore  be  done  with  extreme  care  and  only,  if 
sufficient experience in testing exists. 

•  The  determination  of  the  oxidising  properties  of  an  aqueous  solution  of  solid  oxidising 
substances and the classification as an oxidising mixture is not necessary provided that 
the total concentration of all solid oxidisers in the aqueous solution is less than or equal 
to 20 % (w/w).  

2.13.4.3.  Classification criteria 

The testing procedures for oxidising liquids are based on the capability of an oxidising liquid to 
enhance  the  combustion  of  a  combustible  material.  Therefore,  in  the  applicable  test  method 
substances  and  mixtures  that  are  submitted  for  classification  testing  are  mixed  with  a 
combustible material. Dried fibrous cellulose is used as a combustible material. The mixture of 
the potentially oxidising liquid and cellulose is then ignited, and its behaviour is observed and 
compared to the behaviour of reference materials. 

For  liquids  the  mixture  with  cellulose  is  ignited  under  confinement  in  an  autoclave  and  the 
pressure rise rate that is caused by the ignition and the subsequent reaction is recorded. The 
pressure  rise  rate  is  compared  to  that  of  three  reference  material  mixtures.  The  higher  the 
pressure rise rate, the stronger the oxidising capability of the liquid tested. 

Annex I: 2.13.2.1.  

An oxidising liquid shall be classified in one of the three categories for this class using test 
O.2 in Part III, sub-section 34.4.2 of the UN RTDG, Manual of Tests and Criteria in 
accordance with Table 2.13.1: 

Table 2.13.1 

Criteria for oxidising liquids 

Category  Criteria 

1 

Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or 
mixture) and cellulose tested, spontaneously ignites; or the mean pressure 
rise time of a 1:1 mixture, by mass, of substance (or mixture) and cellulose is 
less than that of a 1:1 mixture, by mass, of 50 % perchloric acid and cellulose. 

 
 
 
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2 

3 

Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or 
mixture) and cellulose tested, exhibits a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 40 % 
aqueous sodium chlorate solution and cellulose; and the criteria for Category 1 
are not met. 

Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or 
mixture) and cellulose tested, exhibits a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 65 % 
aqueous nitric acid and cellulose; and the criteria for Category 1 and 2 are not 
met. 

For additional information regarding the use of non-testing data see the next section and Urben, 
2007 (see section 2.13.7). 

2.13.4.4.  Testing and evaluation of hazard information 

The  test  methods  for  oxidising  liquids  are  designed  to  give  a  final  decision  regarding  their 
classification.  Apart  from  testing,  also  experience  in  the  handling  and  use  of  substances  or 
mixtures  which  shows  them  to  be  oxidising  is  an  important  additional  factor  in  considering 
classification  in  this  hazard  class.  The  CLP  text  comprises  the  following  classification 
consideration: 

Annex I: 2.13.4     Additional Classification Considerations 

2.13.4.3 In the event of divergence between test results and known experience in the 

handling and use of substances or mixtures which shows them to be oxidising, 
judgements based on known experience shall take precedence over test results. 

A substance or mixture must not be classified into a less severe category or as non-oxidising 
based on experience only. 

2.13.4.5.  Decision logic 

Classification of oxidising liquids is done according to decision logic 2.13 as included in GHS. 

NOTE: The person responsible for the classification of oxidising liquids should be experienced 
in this field and be familiar with the criteria for classification. 

 
 
 
 
 
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Figure 2.13 Decision logic for oxidising liquids (Decision logic 2.13 of GHS) 

The substance/mixtures is a liquid 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, exhibits a pressure rise ≥ 2070 kPa (gauge)? 

Yes 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, exhibit a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 
65 % aqueous nitric acid and cellulose? 

No 

No 

Yes 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, exhibit a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 
40 % aqueous sodium chlorate and cellulose? 

No 

Yes 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, spontaneously ignite or exhibit a mean 
pressure rise time less than that of a 1:1 mixture, by mass, of 50 
% perchloric acid and cellulose?  

No 

Yes 

Not 
classified 

Not 
classified 

Category 3 

Warning 

Category 2 

Warning 

Category 1 

Danger 

2.13.4.6.  Hazard communication for oxidising liquids 

2.13.4.6.1.  Pictograms, signal words, hazard statements and precautionary 

statements 

The pictograms and hazard statements are designed to indicate that oxidising substances and 
mixtures  may  cause  or  contribute  to  fire  or  explosion  and  therefore  in  principle  should  be 
separated from combustible materials. 

 
 
 
  
 
 
  
 
  
 
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Annex I: Table 2.13.2 

Label elements for oxidising liquids 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Danger 

Warning 

Hazard Statement 

H271: May cause fire or 
explosion; strong oxidiser 

H272: May intensify 
fire; oxidiser 

H272: May intensify 
fire; oxidiser 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Storage 

Precautionary 
Statement 
Disposal 

P210 

P220 

P280 

P283 

P306 + P360 

P210 

P220 

P280 

P210 

P220 

P280 

P371 + P380 + P37 

P370 + P378 

P370 + P378 

P370 + P378 

P420 

P501 

P501 

P501 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.13.5.  Relation to transport classification 

Division  5.1  within  Class  5  of  the  UN  RTDG  Model  Regulations  covers  oxidising  liquids  and 
oxidising solids, using the same tests and criteria as CLP. Therefore, a liquid substance or mixture 
classified  as  Division  5.1  (sometimes  referred  to  as  Class  5.1)  according  to  any  of  the  modal 
transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) is normally also classified as an 
oxidising  liquid  according  to  CLP.  Packing  Groups  I,  II  and  III  of  the  transport  regulations 
correspond  directly  to  Categories  1,  2  and  3  of  CLP,  respectively.  See  Annex  I  for  additional 
information on transport classification in relation to CLP classification. 

2.13.6.  Example of classification for oxidising liquids 

2.13.6.1.  Example of substances and mixtures fulfilling the classification 
criteria 

The non-exhaustive list of substances and mixtures fulfilling the criteria for classification is only 
presented for information purposes. For examples of results see section 34.4.2.5 of UN-MTC. 

 
 
 
 
 
 
 
 
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•  Ferric nitrate, saturated aqueous solution 

•  Lithium perchlorate, saturated aqueous solution 

•  Magnesium perchlorate, saturated aqueous solution 

•  Perchloric acid, 55 % 

•  Sodium nitrate, 45 % aqueous solution 

2.13.6.2.  Example of substances and mixtures not fulfilling the 
classification criteria 

•  Nickel nitrate, saturated aqueous solution 

•  Potassium nitrate, 30 % aqueous solution 

•  Silver nitrate, saturated aqueous solution 

2.13.7.  Reference 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 
(7th Edition). Elsevier.  

2.14. OXIDISING SOLIDS 

2.14.1.  Introduction 

The criteria for ‘Oxidising solids’ are found in CLP Annex I, section 2.14 and are identical to those 
in chapter 2.14 of GHS18. 

The  hazard  class  oxidising  solids  comprises  substances  and  mixtures  whose  hazard  is 
characterised  by  the  fact  that,  in  contact  with  other  materials,  they  are  able  to  cause  or 
contribute to the combustion of those materials. The other materials do not necessarily have to 
belong to a certain hazard class to be affected by the presence of an oxidising solid. This is for 
example  the  case  when  a  liquid  fuel  (e.g.  gas  oil)  mixes  with  an  oxidising  solid.  Certain 
combinations of combustible materials and oxidising substances or mixtures may even result in 
spontaneous combustion, thermal instability or form an explosive mixture. 

Although  widely  known  as  ‘oxidising  materials’,  their  hazard  and  behaviour  might  be  better 
understood by considering them to be ‘fire enhancing substances’. 

Apart from the combustion hazard, the production of toxic and/or irritating fumes may cause an 
additional  hazard.  For  example,  when  nitrates  are  involved  in  a  fire,  nitrous  fumes  may  be 
formed. 

The testing procedure and criteria for oxidising substances or mixtures are not appropriate for 
ammonium  nitrate-based  products.  For  classification  of  such  products,  experience  should  be 
applied and expert judgement should be sought.  

Ammonium nitrate-based fertilisers are  classified based  on their composition according to the 
UN Manual of Tests and Criteria, section 39. For the classification of ammonium  nitrate-based 
emulsions, suspensions or gels (intermediate for blasting explosives), see section 2.1.  

 
 
 
 
 
 
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2.14.2.  Definitions and general considerations for classification of oxidising 

solids 

The CLP text comprises the following definition for oxidising solids. 

Annex I: 2.14.1.     Definition 

Oxidising solid means a solid substance or mixture which, while in itself is not necessarily 
combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of 
other material. 

Special consideration on particle size 

The oxidising properties of a solid depend on its particle size. Smaller particles  enable a more 
intimate contact between the solid oxidiser and a combustible solid. The smaller the particle size, 
the  higher  the  oxidising  capability  of  the  solid.  As  a  consequence,  it  may  happen  that  large 
particles of a certain solid are considered to be non-hazardous, while small particles of the same 
solid  need  to  be  classified  into  the  hazard  class  of  oxidising  solids.  In  rare  cases,  very  small 
particles of a solid oxidiser may even show explosive properties (e.g. ammonium perchlorate). 

Hence, it is very important that oxidising properties for solids are investigated on the substance 
or mixture as it is actually presented (including how it can reasonably be expected to be used, 
see Article 8 (6) of CLP). This is indicated by the Note 2 cited in CLP Annex I, section 2.14.2.1. 

Annex I: 2.14.2.1.  

[…] 

Note 2: The test shall be performed on the substance or mixture in its physical form as 
presented. If for example, for the purposes of supply or transport, the same chemical is to 
be presented in a physical form different from that which was tested and which is 
considered likely to materially alter its performance in a classification test, the substance 
shall also be tested in the new form. 

2.14.3.  Relation to other physical hazards 

Oxidising  solids  that  are  mixed  with  combustible  materials  or  reducing  agents  may  have 
explosive properties and should be considered for  classification in the hazard class  explosives 
(including the applicable screening procedures), see section 2.1. Such mixtures may also exhibit 
self-reactive behaviour, see section 2.8. Expert judgement should be sought in case of doubt. 

The classification procedure and criteria for oxidising substances and mixtures is not applicable 
for organic peroxides. The majority of the organic peroxides do not possess oxidising properties; 
their  main  hazards  are  reactivity  and  flammability.  Under  CLP,  organic  peroxides  comprise  a 
separate hazard class (CLP Annex I, section 2.15) and they must not be considered according 
to the procedures described for oxidising solids.  

Inorganic  oxidising  solids  are  not  flammable  and  therefore  do  not  need  to  be  subject  to  the 
classification procedures for the hazard classes flammable solids or pyrophoric solids. Also, other 
solids of organic or partially organic nature that are classified as oxidising solids are normally 
not flammable, although a few exceptions may exist. Expert judgement should be sought in case 
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2.14.4.  Classification of substances and mixtures as oxidising solids 

2.14.4.1. 

Identification of hazard information 

Oxidising  solids  may  cause,  or  contribute  to,  the  combustion  of  other  material.  Although  the 
definition in CLP Annex I, section 2.14.1, quoted above,  states that they generally do this by 
yielding  oxygen,  halogens  can  behave  in  a  similar  way.  Therefore,  any  substance  or  mixture 
containing oxygen and/or halogen atoms should in principle be considered for inclusion into the 
hazard  categories  oxidising  solids.  This  does  not  necessarily  mean  that  every  substance  or 
mixture  containing  oxygen  and/or  halogen  atoms  should  be  subjected  to  the  full  testing 
procedure.  

2.14.4.2.  Screening procedures and waiving of testing 

Solids  that  are  classified  as  explosives  should  not  be  subjected  to  the  testing  procedures  for 
oxidising solids. 

Organic  peroxides  should  be  considered  for  classification  within  the  hazard  class  organic 
peroxides, see section 2.15. 

Before  submitting  a  substance  or  a  mixture  to  the  full  test  procedure,  an  evaluation  of  its 
chemical  structure  may  be  very  useful  as  it  may  prevent  unnecessary  testing.  The  person 
applying this procedure should have sufficient experience in testing and in theoretical evaluation 
of hazardous substances and mixtures. The following text provides a guideline for the theoretical 
evaluation  of  potential  oxidising  properties  on  the  basis  of  its  composition  and  chemical 
structure. In case of doubt, the full test must be performed. 

The CLP text comprises the following screening considerations: 

Annex I: 2.14.4.1. 

For organic substances or mixtures the classification procedure for this hazard class need not 
to be applied if: 

(a) 

the substance or mixture does not contain oxygen, fluorine or chlorine; or 

(b) 

the substance or mixture contains oxygen, fluorine or chlorine and these elements are 
chemically bonded only to carbon or hydrogen. 

2.14.4.2. 

For inorganic substances or mixtures, the classification procedure for this hazard class need 
not be applied if they do not contain oxygen or halogen. 

On the basis of this theoretical evaluation a distinction can only be made between ‘potentially 
oxidising’ (i.e. further testing required) and ‘non-oxidising’ (i.e. no further testing for this hazard 
class  required).  It  is  not  possible  to  assign  a  hazard  category  on  the  basis  of  a  theoretical 
evaluation. Even though for ‘potentially oxidising’ substances, classification cannot be excluded 
based on theoretical evaluation, in some cases it might not be necessary to test a substance or 
mixture. However, this decision requires expert judgement. 

Any substance or mixture that complies with the above waiving criteria can be safely regarded 
to have no oxidising properties and, hence, does not to be tested and should not be regarded as 
an  oxidising  solid.  However,  such  a  substance  or  mixture  may  still  possess  other  hazardous 
properties that require classification into another hazard class. 

In case a mixture of an oxidising substance and a non-hazardous inert substance is offered for 
classification, the following should be taken into account: 

 
 
 
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•  An  inert  material  by  definition  does  not  contribute  to  the  oxidising  capability  of  the 
oxidising substance. Hence, the mixture can never be classified into a more severe hazard 
category. 

• 

If an oxidising substance is mixed with an inert material, the oxidising capability of the 
mixture does not linearly decrease with decreasing content of oxidising substance. The 
relationship is more or less logarithmic and depends on the characteristics of the oxidising 
substance. For instance, a mixture containing 50 % of a strong oxidiser and 50 % of an 
inert  material  may  retain  90  %  of  the  oxidising  capability  of  the  original  oxidising 
component.  Non-testing  classification  of  mixtures  based  solely  on  test  data  for  the 
original  oxidising  substance  should  therefore  be  done  with  extreme  care  and  only  if 
sufficient experience in testing exists. 

2.14.4.3.  Classification criteria 

The testing procedures for oxidising solids are based on the capability of an oxidising solid to 
enhance  the  combustion  of  a  combustible  material.  Therefore,  in  the  applicable  test  method 
solids that are submitted to classification testing are mixed with a combustible material. Dried 
fibrous cellulose is used as a combustible material. The mixture of the potentially oxidising solid 
and cellulose is then ignited, and its behaviour is observed and compared to the behaviour of 
reference material mixtures. 

For solids, the mixture with cellulose is ignited at atmospheric conditions and the time necessary 
for the combustion reaction to consume the mixture is recorded. The faster the combustion rate, 
the stronger the oxidising capability of the solid tested. 

The UN-MTC currently has two methods for the determination of oxidising properties of solids, 
i.e.  tests  O.1  and  O.3.  In  test  O.1,  the  reaction  between  the  oxidiser  and  the  combustible 
material is observed visually while in test O.3 a gravimetric method is applied. Both methods 
can be used although in certain cases the one or the other method may be preferred. In this 
case, expert judgement should be sought. 

Annex I: 2.14.2.1. An oxidising solid shall be classified in one of the three categories for this 
class using test O.1 in Part III, sub-section 34.4.1 or test O.3 in Part III, sub-section 34.4 3 of 
the UN RTDG, Manual of Tests and Criteria, in accordance with Table 2.14.1: 

Table 2.14.1 

Criteria for oxidising solids 

Category  Criteria using test O.1  

Criteria using test O.3 

1 

2 

3 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
time less than the mean burning time of 
a 3:2 mixture, (by mass), of potassium 
bromate and cellulose. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
rate greater than the mean burning rate 
of a 3:1 mixture (by mass) of calcium 
peroxide and cellulose. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
time equal to or less than the mean 
burning time of a 2:3 mixture (by mass) 
of potassium bromate and the criteria 
for Category 1 are not met. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
rate equal to or greater than the mean 
burning rate of a 1:1 mixture (by mass) 
of calcium peroxide and cellulose and 
the criteria for Category 1 are not met. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 

 
 
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mass) tested, exhibits a mean burning 
time equal to or less than the mean 
burning time of a 3:7 mixture (by mass) 
of potassium bromate and cellulose and 
the criteria for Categories 1 and 2 are 
not met. 

mass) tested, exhibits a mean burning 
rate equal to or greater than the mean 
burning rate of a 1:2 mixture (by mass) 
of calcium peroxide and cellulose and 
the criteria for Categories 1 and 2 are 
not met. 

Note 1  
Some oxidising solids also present explosion hazards under certain conditions (when stored in 
large quantities). Some types of ammonium nitrate may give rise to an explosion hazard 
under extreme conditions and the 'Resistance to detonation test' (IMSBC Code (International 
Maritime Solid Bulk Cargoes Code, IMO), Appendix 2, Section 5) can be used to assess this 
hazard. Appropriate information shall be made in the SDS. 

Note  1  may  also  apply  to  other  oxidising  ammonium  salts.  Experience  indicates  that  the 
conditions required for ammonium nitrate to present an explosion hazard involve a combination 
of  factors,  such  as  storage  in  large  volumes  (multiple  tonnes)  and  either  contamination  (e.g. 
with metals, acids, organics) or excessive heat (e.g. under conditions of fire). The resistance to 
detonation (RTD) test is extensively described in Regulation (EC) No 2019/1009 for ammonium 
nitrate. 

For  additional  information  regarding  the  use  of  non-testing  data  see  CLP,  Annex  I  section 
2.14.4.3 below and Urben, 2007 (see section 2.14.7). 

2.14.4.4.  Testing and evaluation of hazard information 

The  test  methods  for  oxidising  solids  are  designed  to  give  a  final  decision  regarding  their 
classification.  Apart  from  testing,  also  experience  in  the  handling  and  use  of  substances  or 
mixtures  which  shows  them  to  be  oxidising  is  an  important  additional  factor  in  considering 
classification  in  this  hazard  class.  The  CLP  text  comprises  the  following  classification 
consideration: 

Annex I: 2.14.4     Additional Classification Considerations 

2.14.4.3 In the event of divergence between test results and known experience in the 
handling and use of substances or mixtures which shows them to be oxidising, judgements 
based on known experience shall take precedence over test results. 

A substance or mixture must not be classified into a less severe category or as non-oxidising 
based on experience only. 

2.14.4.5.  Decision logic 

Classification of oxidising solids is done according to decision logic 2.14 as included in GHS. 

NOTE:  The  person  responsible  for  the  classification  of  oxidising  solids  should  be 
experienced in this field and be familiar with the criteria for classification. 

 
 
 
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Figure 2.14 Decision logic for oxidising solids (Decision logic 2.14 of GHS) 

The substance/mixture is a solid 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, tested 
ignite or burn? 

No 

Not 
classified 

Yes 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, tested 
exhibit a mean burning time ≤ the mean burning time of a 3:7 
mixture, by mass, by potassium bromate and cellulose? 

Or 

a mean burning rate ≥ the mean burning rate of a 1:2 mixture, by 
mass, of a calcium peroxide and cellulose? 

No 

Not 
classified 

Category 3 

Yes 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, test exhibit 
a mean burning time ≤ the mean burning time of a 2:3 mixture, by 
mass, of potassium bromate and cellulose? 

No 

Warning 

a mean burning rate ≥  the mean burning rate of a 1:1 mixture, by 
mass, of a calcium peroxide and cellulose? 

Or 

Yes 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, tested 
exhibit a mean burning time < the mean burning time of a 3:2 
mixture, by mass, of potassium bromate and cellulose? 

Or 

a mean burning rate > the mean burning rate of a 3:1 mixture, by 
mass, of a calcium peroxide and cellulose? 

Yes 

Category 2 

No 

Danger 

Category 1 

Danger 

 
 
 
  
 
  
 
 
  
 
  
 
  
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2.14.5.  Hazard communication for oxidising solids 

2.14.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

The pictograms and hazard statements are designed to indicate that oxidising substances and 
mixtures  may  cause  or  contribute  to  fire  or  explosion  and  therefore  in  principle  should  be 
separated from combustible materials. 

Annex I: Table 2.14.2 

GHS Pictograms 

Label elements for oxidising solids 

Category 1 

Category 2 

Category 3 

Signal Word 

Danger 

Danger 

Warning 

Hazard Statement 

H271: May cause fire or 
explosion; strong oxidiser 

H272: May intensify 
fire; oxidiser 

H272: May intensify 
fire; oxidiser 

Precautionary 
Statement Prevention 

Precautionary 
Statement Response 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

P210 

P220 

P280 

P283 

P306 + P360 

P210 

P220 

P280 

P210 

P220 

P280 

P371 + P380 + P37 

P370 + P378 

P370 + P378 

P370 + P378 

P420 

P501 

P501 

P501 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.14.6.  Relation to transport classification 

Division  5.1  within  Class  5  of  the  UN  RTDG  Model  Regulations  covers  oxidising  liquids  and 
oxidising solids, using the same tests and criteria as CLP. Therefore, a solid substance or mixture 
classified  as  Division  5.1  (sometimes  referred  to  as  Class  5.1)  according  to  any  of  the  modal 
transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) is normally also classified as an 
oxidising  solid  according  to  CLP.  Packing  Groups  I,  II  and  III  of  the  transport  regulations 
correspond  directly  to  Categories  1,  2  and  3  of  CLP,  respectively.  See  Annex  I  for  additional 
information on transport classification in relation to CLP classification. 

 
 
 
 
 
 
 
 
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2.14.7.  Example of classification for oxidising solids 

2.14.7.1.  Example of substances and mixtures fulfilling the classification 
criteria 

The non-exhaustive list of substances and mixtures fulfilling the criteria for classification is only 
presented for information purposes. Note that oxidising properties of these substances may differ 
depending on particle size. For examples of results see section 34.4.3.6 of UN-MTC. 

•  Calcium nitrate, anhydrous 

•  Chromium trioxide 

•  Potassium nitrite 

•  Potassium nitrate 

•  Potassium perchlorate 

•  Potassium permanganate 

•  Sodium chlorate 

•  Sodium nitrite 

•  Sodium nitrate 

•  Strontium nitrate, anhydrous 

2.14.7.2.  Example of substances and mixtures not fulfilling the 
classification criteria 

•  Calcium nitrate, tetrahydrate 

•  Cobalt nitrate, hexahydrate 

2.14.8.  Reference 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 
(7th Edition). Elsevier.  

2.15. ORGANIC PEROXIDES 

2.15.1.  Introduction 

The criteria for ‘Organic peroxides’ are found in CLP Annex I, section 2.15 and are identical to 
those in chapter 2.15 of GHS18. 

The hazard class organic peroxides is unique in the respect that it is the only category to which 
chemicals are assigned on the basis of their chemical structure. Being an organic peroxide cannot 
be seen as an ‘intrinsic property’ per se but all organic peroxides have intrinsic properties that 
are  hazardous  as  they  are  thermally  unstable  substances  or  mixtures,  which  can  undergo 
exothermic  self-accelerating  decomposition.  However,  the  hazardous  nature  of  a  peroxide  is 
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2.15.2.  Definitions and general considerations for classification of organic 

peroxides 

In CLP, the following definition is given for organic peroxides. 

Annex I: 2.15.1.     Definition  

Organic peroxides means liquid or solid organic substances which contain the bivalent -O-O- 
structure and may be considered derivatives of hydrogen peroxide, where one or both of the 
hydrogen atoms have been replaced by organic radicals. The term organic peroxide includes 
organic peroxide mixtures (formulations) containing at least one organic peroxide. Organic 
peroxides are thermally unstable substances or mixtures, which can undergo exothermic self-
accelerating decomposition. In addition, they can have one or more of the following 
properties: 

(i) be liable to explosive decomposition; 

(ii) burn rapidly; 

(iii) be sensitive to impact or friction; 

(iv) react dangerously with other substances. 

2.15.1.2. An organic peroxide is regarded as possessing explosive properties when in 
laboratory testing the mixture (formulation) is liable to detonate, to deflagrate rapidly or to 
show a violent effect when heated under confinement. 

2.15.3.  Relation to other physical hazards 

In addition to the definition (CLP Annex I, section 2.15.1), organic peroxides may: 

a.  be flammable; 

b.  emit flammable gas when heated. 

In general, organic peroxides do not have or have only weak oxidising properties and typically 
do not require additional classification as oxidising solids or liquids. 

The  additional  (subsidiary)  labelling,  as  indicated  in  the  list  of  classified  organic  peroxides 
included  in  the  UN  RTDG  Model  Regulations,  section  2.5.3.2.4,  represents  the  additional 
hazardous properties.  

Neither  the  burning  properties  nor  the  sensitivity  to  impact  and  friction  form  part  of  the 
classification  procedure  for  organic  peroxides  in  CLP.  However,  these  properties  may  be  of 
importance for the safe handling of organic peroxides (see section 2.15.4.3.2 additional testing). 

In addition, the following should be noted: 

Explosive properties 

The explosive properties do not have to be determined according to CLP Annex I, section 2.1, 
because explosive properties are already incorporated in the classification of organic peroxides. 

2.15.4.  Classification of substances and mixtures as organic peroxides 

2.15.4.1. 

Identification of hazard information 

As a consequence of the hazard class definition, if the chemical structure does not contain the 
bivalent -O-O- structure, the substance is not classified as organic peroxide. 

The  classification  of  an  organic  peroxide  in  one  of  the  seven  categories  ‘Types  A  to  G’  is 
dependent  on  its  detonation,  deflagration  and  thermal  explosion  properties,  its  response  to 
heating under confinement, its explosive power and the concentration and  the type of diluent 
added to desensitise the organic peroxide. Specifications of acceptable diluents that can be used 

 
 
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safely  are  given  in  the  UN  RTDG  Model  Regulations,  2.5.3.5.  The  classification  of  an  organic 
peroxide as Type A, B or C is dependent on the type of packaging in which the organic peroxide 
is tested as it affects the degree of confinement to which the organic peroxide is subjected. This 
has to be considered when handling the organic peroxide; stronger packaging may result in more 
violent reactions when the organic peroxide decomposes. This is why it is important that storage 
and transport is done in packaging, allowed for the type of organic peroxide, that conforms the 
requirements of the UN-packaging or IBC41 instruction (P520/IBC520) or tank instruction (T23). 

2.15.4.2.  Classification criteria 

Annex I: 2.15.2.1. Any organic peroxide shall be considered for classification in this class, 
unless it contains: 

a) not more than 1,0 % available oxygen from the organic peroxides when containing not 

more than 1,0 % hydrogen peroxide; or 

b) not more than 0,5% available oxygen from the organic peroxides when containing more 

than 1,0 % but not more than 7,0 % hydrogen peroxide. 

[…] 

In  CLP  decision  logic  Annex  I,  Figure  2.15.1,  classification  of  organic  peroxides  is  based  on 
performance-based testing both small scale tests and, where necessary, some larger scale test 
with the organic peroxide in its packaging.  

Organic peroxides are classified into one of the seven categories of ‘Types A to G’ according to 
the classification  criteria of  CLP. The classification principles are given in decision logic Figure 
2.15.1 of CLP and the Test Series A to H, as described in the Part II of the UN-MTC, should be 
performed. 

Annex I: 2.15.2.2. Organic peroxides shall be classified in one of the seven categories of 
‘Types A to G’ for this class, according to the following principles: 

(a) any organic peroxide which, as packaged, can detonate or deflagrate rapidly shall be 

defined as organic peroxide TYPE A; 

(b) any organic peroxide possessing explosive properties and which, as packaged, neither 
detonates nor deflagrates rapidly, but is liable to undergo a thermal explosion in that 
package shall be defined as organic peroxide TYPE B; 

(c) any organic peroxide possessing explosive properties when the substance or mixture as 
packaged cannot detonate or deflagrate rapidly or undergo a thermal explosion shall be 
defined as organic peroxide TYPE C; 

(d) any organic peroxide which in laboratory testing: 

(i) detonates partially, does not deflagrate rapidly and shows no violent effect when 

heated under confinement; or 

(ii) does not detonate at all, deflagrates slowly and shows no violent effect when 

heated under confinement; or 

(iii) does not detonate or deflagrate at all and shows a medium effect when heated 

under confinement; 

shall be defined as organic peroxide TYPE D; 

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(e) any organic peroxide which, in laboratory testing, neither detonates nor deflagrates at all 

and shows low or no effect when heated under confinement shall be defined as organic 
peroxide TYPE E; 

(f) any organic peroxide which, in laboratory testing, neither detonates in the cavitated state 

nor deflagrates at all and shows only a low or no effect when heated under confinement as 
well as low or no explosive power shall be defined as organic peroxide TYPE F; 

(g) any organic peroxide which, in laboratory testing, neither detonates in the cavitated state 

nor deflagrates at all and shows no effect when heated under confinement nor any 
explosive power, provided that it is thermally stable, i.e. the SADT is 60 oC or higher for a 
50 kg package(1), and, for liquid mixtures, a diluent having a boiling point of not less than 
150 oC is used for desensitisation, shall be defined as organic peroxide TYPE G. If the 
organic peroxide is not thermally stable or a diluent having a boiling point less than 150 oC 
is used for desensitisation, the organic peroxide shall be defined as organic peroxide 
TYPE F. 

Where the test is conducted in the package form and the packaging is changed, a further test 
shall be conducted where it is considered that the change in packaging will affect the outcome 
of the test. 

(1) See UN RTDG, Manual of Test and Criteria, sub-sections 28.1, 28.2, 28.3 and Table 28.3. 

For reference, a list of currently classified organic peroxides is included in the UN RTDG Model 
Regulations, section 2.5.3.2.4. 

2.15.4.3.  Testing and evaluation of hazard information 

2.15.4.3.1.  Thermal stability tests and temperature control 

In addition to the classification tests given in decision logic Figure 2.15.1 of CLP, the thermal 
stability of the organic peroxide has to be assessed to determine the SADT. For the determination 
of the SADT, the testing method in UN-MTC, section 28, may be used. 

The SADT is defined as the lowest temperature at which self-accelerating decomposition of an 
organic peroxide may occur in the packaging as used in transport, handling and storage. The 
SADT is a measure of the combined effect of the ambient temperature, decomposition kinetics, 
package size and the heat transfer properties of the organic peroxide and its packaging. 

There is no relation between the SADT of an organic peroxide and its classification in one of the 
seven categories ‘Types A to G’. The SADT is used to derive safe handling, storage and transport 
temperatures (control temperature) and alarm temperature (emergency temperature).   

Depending on its SADT an organic peroxide needs temperature control and the rules as given in 
CLP Annex I, section 2.15.2.3, consist of the following two elements: 

1.  Criteria for temperature control: 

The following organic peroxides need to be subjected to temperature control: 

a.  Organic peroxide types B and C with a SADT ≤ 50 °C; 

b.  Organic peroxide type D showing a medium effect when heated under 

confinement with a SADT ≤ 50 °C or showing a low or no effect when heated 
under confinement with a SADT ≤ 45 °C; and 

c.  Organic peroxide types E and F with a SADT ≤ 45 °C. 

 
 
 
 
 
 
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2.  Derivation of control and emergency temperatures: 

Type of receptacle 

SADT * 

Control temperature  Emergency 

temperature 

Single packaging and 
IBC’s 

20 °C or less 

20 °C below SADT 

10 °C below SADT 

over 20 °C to 35 °C 

15 °C below SADT 

10 °C below SADT 

over 35 °C 

10 °C below SADT 

5 °C below SADT 

Tanks 

< 50 °C 

10 °C below SADT 

5 °C below SADT 

* i.e. the SADT of the organic peroxide as packaged for transport, handling and storage 

It should be emphasised that the SADT is dependent on the nature of the organic peroxide itself, 
together with the volume and heat-loss characteristics of the packaging or vessel in which the 
organic peroxide is handled. The temperature at which self-accelerating decomposition occurs 
falls: 

•  as the size of the packaging or vessel increases; and 

•  with increasing efficiency of the insulation on the package or vessel. 

The SADT is only valid for the organic peroxide as tested and when handled properly. Mixing the 
organic  peroxide  with  other  chemicals,  or  contact  with  incompatible  materials  (including 
incompatible  packaging  or  vessel  material)  may  reduce  the  thermal  stability  due  to  catalytic 
decomposition, and lower the SADT. This may increase the risk of decomposition and has to be 
avoided. 

2.15.4.3.2.  Additional considerations and testing 

Explosive properties 

The sensitivity of organic peroxides to impact (solids and liquids) and friction (solids only) may 
be of importance for the safe handling of the organic peroxide if they have pronounced explosive 
properties (e.g. they are liable to detonate, to deflagrate rapidly or show a violent effect when 
heated under confinement). Test methods to determine these properties are described in Test 
Series 3 of the UN-MTC (see Test 3 (a) (ii) and 3 (b) (i)). This information on the mechanical 
sensitivity could be included in the SDS. 

Burning properties 

In some national storage guidelines, the burning rate is commonly used for classification for the 
purposes of storage and consequential storage requirements. Test methods are incorporated in 
these national storage regulations. 

Flash point 

The flash point for liquid organic peroxides is only relevant in the temperature range where the 
organic peroxide is thermally stable. Above the SADT of the organic peroxide, determination of 
the flash point is not relevant because decomposition products evolve. 

NOTE:  In  case  a  flash  point  determination  seems  reasonable  (expected  flash  point  below 
the SADT) a test method using small amount of sample is recommended. In case the organic 
peroxide is diluted or dissolved, the diluent may determine the flash point. 

Auto-ignition temperature 

The  determination  of  the  auto  ignition  temperature  is  not  relevant  for  organic  peroxides. 
Available  test  methods  are  for  non-decomposing  vapour  phases,  but  the  vapours  of  organic 
peroxides decompose during execution of the test and auto ignition of these organic peroxide 
vapours can never be excluded. This information should be included in the SDS.  

 
 
 
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Self-ignition temperature 

The determination of the self-ignition temperature (applicable for solids) is not relevant, since 
the thermal stability of organic peroxides is quantitatively given by the SADT. 

Control and Emergency temperatures 

The Control and Emergency temperatures are based on the SADT as in most cases determined 
by UN Test Series H. In UN Test Series H.2 and H.3, the heat loss applied in the calculating the 
SADT should be representative for the packaging, IBC, tank or vessel in which the substance or 
mixture  is  handled  or  stored.  In  UN  Test  H.4,  the  Dewar  vessel  used  is  supposed  to  be 
representative for the organic peroxide handled in packages. For handling the organic peroxide 
in  larger  quantities  (IBCs/tanks/vessels  etc.)  and/or  in  (thermally)  insulated  containers,  the 
SADT has to be determined for that quantity with that degree of insulation. From that SADT the 
Control and Emergency temperatures can be derived (see also section 2.15.4.3.1). 

2.15.4.3.3.  Additional classification considerations 

Currently the following properties are not incorporated in the classification of organic peroxides 
under CLP: 

•  mechanical sensitivity i.e. impact and friction sensitivity (for handling purposes); 

•  burning properties (for storage purposes); 

• 

flash point for liquids; and 

•  burning rate for solids. 

Furthermore: 

Annex I: 2.15.4.2. Mixtures of already classified organic peroxides may be classified as the 
same type of organic peroxide as that of the most dangerous component. However, as two 
stable components can form a thermally less stable mixture, the SADT of the mixture shall 
be determined. 

Note: The sum of the individual parts can be more hazardous than the individual 
components. 

2.15.4.4.  Decision logic 

The decision logic for organic peroxides is applicable according to CLP.  

NOTE:  The  person  responsible  for  the  classification  of  organic  peroxides  should  be 
experienced in this field and be familiar with the criteria for classification. 

 
 
 
 
 
 
 
 
 
 
 
 
 
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Annex I: Figure 2.15.1 

Organic Peroxide 

 
 
 
 
 
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2.15.5.  Hazard communication for organic peroxides 

2.15.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

According to CLP the following label elements must be used for organic peroxide meeting the 
criteria for this hazard class: 

Annex I: Table 2.15.1 

Label elements for organic peroxides 

Classification  Type A 

Type B 

Type C & D 

Type E & F 

Type G1 

GHS 
pictograms 

Signal Word 

Danger 

Danger 

Danger 

Warning 

Hazard 
Statement 

H240: 
Heating may 
cause an 
explosion 

H241: 
Heating may 
cause a fire 
or explosion 

H242: 
Heating may 
cause a fire 

H242: 
Heating may 
cause a fire 

Precautionary 
statement 

Prevention 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

Precautionary 
statement 

P370 + P372 
+ 

P370 + P380 
+ 

P370 + P378  P370 + P378 

There are no 
label elements 
allocated to 
this hazard 
category 

Response  

P380 + P373 

Precautionary 
statement 

Storage 

Precautionary 
statement 

Disposal 

P403 

P410 

P411 

P420 

P501 

P375[+ 
P378]2 

P403 

P410 

P411 

P420 

P501 

P403 

P410 

P411 

P420 

P501 

P403 

P410 

P411 

P420 

P501 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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1 Type G has no hazard communication elements assigned but should be considered for 
properties belonging to other hazard classes. 

2 See introduction to Annex I for details on the use of square brackets. 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.15.5.2.  Additional labelling provisions 

Additional hazardous properties, resulting in additional (subsidiary) labelling, are indicated in the 
list of classified organic peroxides included in the UN RTDG Model Regulations, section 2.5.3.2.4. 

2.15.6.  Relation to transport classification 

Division 5.2 within Class 5 of the UN RTDG Model Regulations covers organic peroxides. A list of 
currently  classified  organic  peroxides  is  included  in  the  UN  RTDG  Model  Regulations,  section 
2.5.3.2.4. This table includes organic peroxides Type B - Type F (and some formulations Type 
G, so-called exempted organic peroxides).  

An exceptional case in this respect is a peroxyacetic acid formulation, as currently classified in 
the  UN  RTDG  Model  Regulations  under  UN  3149,  with  the  following  description:  HYDROGEN 
PEROXIDE  AND  PEROXYACETIC  ACID  MIXTURE  with  acid(s),  water  and  not  more  than  5  % 
peroxyacetic  acid,  STABILISED.  In  the  classification  procedure  for  organic  peroxides,  see 
decision logic in section 2.15.4.4, this formulation will be assigned to organic peroxide Type G, 
and consequently no label elements are allocated. In view of the above, this formulation can be 
classified,  also  in  accordance  with  CLP,  as  an  oxidising  liquid,  category  2.  See  Annex  I  for 
additional information on transport classification in relation to CLP classification. 

2.15.7.  Example of classification for organic peroxides 

2.15.7.1.  Example of substances and mixtures fulfilling the classification 
criteria 

Substance to be classified: Example Peroxide 

Molecular formula: n.a. 

According to CLP Annex I, section 2.15.2.1, the substance has an active oxygen content of 7.40 
% and has to be considered for classification in the hazard class organic peroxides. 

Test results and classification according to CLP decision logic 2.15.1 for organic peroxides and 
the UN-MTC, Part II, is as follows: 

CLASSIFICATION TEST RESULTS 

1. Name of the organic peroxide: 

Example Peroxide 

2. General data 

2.1. 

Composition: 

Example Peroxide, technically pure (97 %) 

2.2. 

Molecular formula: 

Not applicable 

2.3. 

Active oxygen content: 

2.4. 

Physical form: 

2.5. 

Colour: 

2.6. 

Density (apparent): 

7.18 % 

Liquid 

Colourless 

900 kg/m3 

 
 
 
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CLASSIFICATION TEST RESULTS 

3. Detonation (Test Series A) 

Box 1 of the decision logic: 

Does the peroxide propagate a detonation? 

3.1. 

Method: 

UN Test A.1: BAM 50/60 steel tube test 

3.2. 

Sample conditions: 

Peroxide assay 97 % 

3.3. 

Observations: 

Fragmented part of the tube: 18 cm 

3.4. 

Result: 

3.6. 

Exit: 

4. Deflagration (Test Series C) 

No 

1.3 

Box 5 of the decision logic: 

Can the peroxide propagate a deflagration? 

4.1. 

Method 1: 

Time/pressure test (Test C.1) 

4.1.1. 

Sample conditions: 

Ambient temperature 

4.1.2.  Observations: 

4.1.3. 

Result: 

4000 ms 

Yes, slowly 

4.2. 

Method 2: 

Deflagration test (Test C.2) 

4.2.1. 

Sample conditions: 

Temperature: 25 °C 

4.2.2.  Observations: 

Deflagration rate: 0.74 mm/s 

4.2.3. 

Result: 

4.3. 

Final result: 

4.4. 

Exit: 

Yes, slowly 

Yes, slowly 

5.2 

5. Heating under confinement (Test Series E) 

Box 8 of the decision logic: 

What is the effect of heating it under 
confinement? 

5.1. 

Method 1: 

Koenen test (Test E.1) 

5.1.1. 

Sample conditions: 

- 

5.1.2.  Observations: 

Limiting diameter: 2.0 mm  

Fragmentation type ‘F’ 

5.1.3. 

Result: 

Violent 

5.2. 

Method 2: 

Dutch pressure vessel test (test E.2) 

5.2.1. 

Sample conditions: 

- 

5.2.2.  Observations: 

Limiting diameter: 6.0 mm (with 10 g) 

5.2.3. 

Result: 

Medium 

 
 
 
 
 
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CLASSIFICATION TEST RESULTS 

5.3. 

Final result: 

5.4. 

Exit: 

Violent 

8.1 

6. Explosion test in package (Test Series G) 

Box 10 of the decision logic: 

Can it explode as packaged? 

6.1. 

Method: 

Thermal explosion test in package (Test G.1) 

6.2. 

Sample conditions: 

30 litre packaging, 

6.3. 

Observations: 

No fragmentation (N.F.) 

6.4. 

Result: 

6.5. 

Exit: 

No 

10.2 

7. Thermal stability (outside of the decision logic) 

7.1. 

Method: 

Heat accumulation storage test (Test H.4) 

7.2. 

Sample conditions: 

Mass 380 g. Half-life time of cooling of Dewar 
vessel with400 ml DMP: 

10.0 h (representing substance in package) 

7.3. 

Observations: self 

Accelerating decomposition at 35 °C 

7.4. 

Result: 

8. General remarks: 

9. Final classification 

Hazard class: 

Label:  

Signal word: 

No self-accelerating decomposition at 30 °C 

SADT 35 °C 

The decision logic is given in Figure x42 

Organic peroxide, Type C, liquid, temperature 
controlled 

Flame (GHS02) 

Danger 

Hazard statement: 

H242: Heating may cause a fire 

Temperature control: 

Needed based on SADT (35 °C, in package) 

Control temperature*: 

20 °C (in package) 

Emergency temperature*: 

25 °C (in package) 

*see UN-MTC, table 28.2. 

42 Not attached to this example. 

 
 
 
 
 
 
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2.15.7.2.  Additional remarks 

Explosive properties 

As shown in section 2.15.7.1 a substance and a mixture may have explosive properties when 
handled under greater confinement and where the packaging in which it was tested in UN Test 
G.1  (see  point  6  of  classification  test  results  above)  is  changed.  Such  information  should  be 
given in the SDS. 

The  example  in  section  2.15.7.1  shows  a  violent  effect  when  heated  under  confinement  (see 
point 5.3 of the above results). Consequently, also the impact sensitivity according to UN Test 
Series 3, Test 3 (a) (ii), BAM43 Fallhammer should be determined. For this example, it amounts 
to 20 J. Such information should be given in the SDS. 

Burning properties 

For the example in section 2.15.7.1, the burning properties as determined by the test method 
described  in  the  storage  guidelines,  currently  in  place  in  France,  Germany,  Netherlands  and 
Sweden, is 7.0 kg/min/m². Based on this figure and the classification as organic peroxide type 
C, the storage classification can be assigned in those countries. 

Flash point 

The example substance thermally decomposes before the temperature at which the vapour can 
be  ignited  is  reached  (see  section  2.15.4.3)  and  consequently  a  flash  point  cannot  be 
determined. 

2.16. CORROSIVE TO METALS 

2.16.1.  Introduction 

The criteria for ‘Corrosive to metals’ are found in CLP Annex I, section 2.16 and are identical to 
those in chapter 2.16 of GHS18. 

A substance or a mixture that is corrosive to metal under normal conditions is a substance or a 
mixture  liable  to  undergo  an  irreversible  electrochemical  reaction  with  metals  that  leads  to 
significant damage or, in some cases, even to full destruction of the metallic components. The 
corrosive  to  metal  property  is  a  quite  complex  property,  since  it  is  a  substance  (or  mixture) 
related  as  well  as  a  material  (metal)  related  property.  This  means  a  corrosive  substance  or 
mixture leads to corroded material (metal), according to a number of external conditions. From 
the  material  side,  many  types  of  corrosion  processes  may  occur,  according  to  configurations, 
liquid  or  fluid  media  inducing  the  corrosion  process,  nature  of  metal,  potential  passivation 
occurring by oxide formation during corrosion. 

From the substance or mixture side, many parameters may influence the corrosion properties of 
a substance or mixture, such as the nature of the chemical or the pH. From an electrochemistry 
point  of  view,  corrosion  conditions  are  often  studied  using  Pourbaix  diagrams,  which  plot  the 
electrochemical potential (in Volt) that develops according to electrical charges transfer versus 
the pH-value. Such  a diagram is  shown for the  case of iron and applies only for  carbon steel 
corrosion (Jones, 1996). 

43 BAM: Bundesanstalt für Materialforschung und -prüfung 

 
 
 
 
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Figure 2.15 Potential pH (also called Pourbaix) diagram for iron in water at 25 °C, indicating 
stable form of the Fe element and implicitly, corrosion domains 

For  the  purposes  of  CLP,  corrosion  to  metal  will  only  be  considered,  by  pure  convention,  for 
substances and mixtures that are liable to attack carbon steel or aluminium, two of the most 
common  metals  that  may  come  in  contact  with  chemical  substances  (containment  material, 
reactor material). The classification scheme applied here must not be considered as a material 
(metal) classification method for metals regarding resistance to corrosion. By no means steel or 
aluminium specimens that are treated to resist to corrosion, must be selected for testing. 

2.16.2.  Definitions and general considerations for classification of corrosive 

to metals 

CLP comprises the following definition for substances and mixtures that are corrosive to metal. 

Annex I: 2.16.1.     Definition 

A substance or a mixture that is corrosive to metals means a substance or a mixture which by 
chemical action will materially damage, or even destroy, metals. 

2.16.3.  Relation to other physical hazards 

There is no direct relation to other physical hazards. 

2.16.4.  Classification of substances and mixtures as corrosive to metals 

2.16.4.1. 

Identification of hazard information 

Importance of the physical state of the test substance or mixture 

There is no reference in the definition (CLP Annex I, section 2.16.1) to the physical state of the 
substances or mixtures that need consideration for potential classification in this hazard class. 
According  to  the  test  method  for  considering  classification  under  this  hazard  class,  it  can  be 
stated at least that gases are out of the scope of the corrosive to metal hazard class. Neither 
the corrosivity of gases nor the formation of corrosive gases is currently covered by CLP classes 
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Based on practical considerations, only substances and mixtures for which the application of the 
UN  Test  C.1  (described  in  part  III,  section  37.4.1  of  the  UN-MTC)  is  relevant  need  to  be 
considered.  Application  of  classification  criteria  in  the  UN-MTC,  Section  37.4  excludes  solids, 
while ‘liquids and solids that may become liquids (during transport)’, have to be considered for 
such a classification. 

The wording ‘solids that may become liquids’ was developed for the UN RTDG Model Regulations 
classification purposes  and needs further explanation. One common  way by which solids may 
become  liquids  is  by  melting  (due  to  increase  in  temperature).  Solids  having  a  melting  point 
lower than 55 °C (which is the test temperature required in UN Test C.1) must then be taken 
into consideration. Another common physical way to transform a solid into liquid is by dissolution 
in water or another solvent. Classification of solid substances that may become liquids, such as 
through water intake from humid air environments, requires further expert judgement and may 
need adaptation of the classification criteria or test protocol (see section 2.16.4.4.2). Interaction 
with liquids may come from air moisture or unintentional contact with water. Other solvent traces 
may result from the extraction process during manufacturing, and these may induce corrosion 
in practice, as far as it allows some mobility of subsequent ions. Expert judgement would also 
be  required  for  low  melting  point  solids  that  also  partially  convert  into  gas  phase  through 
sublimation process (e.g. methyl isothiocyanate). 

Substances and mixtures in a liquid state must be tested without any modification before testing. 
It should be specified how such substances or mixtures are prepared (transformed into liquids) 
to be able to determine their corrosivity to metals. As an example, it is thought that the quantity 
of solvent (water or any other solvent) to liquefy the test substance before testing would greatly 
influence results of the UN Test C.1 test and may not necessarily represent the real-life situation 
of a product during transport, handling or use.  

Non-testing data 

Following parameters are helpful to evaluate corrosive properties before testing: 

•  melting points for solids; 

• 

chemical nature of the substances and mixtures under evaluation (e.g. strong acids);  

•  pH values (liquids). 

See  also  IR  &  CSA,  Chapter  R.7a:  Endpoint  specific  guidance,  section  R.7.1.2  (Melting 
point/freezing point). 

Literature  may  also  provide  information  on  widely  used  substances  and  liquids  ‘compatibility 
tables’, taking account of the corrosiveness of the products that may serve to decide whether 
testing  must  be  conducted  before  assigning  the  corrosive  to  metals  hazard  class,  on  basis  of 
expert judgement. 

The following substances and mixtures should be considered for classification in this class: 

• 

• 

• 

substances and mixtures having acidic or basic functional groups; 

substances or mixtures containing halogen; 

substances able to form complexes with metals and mixtures containing such 
substances. 

2.16.4.2.  Screening procedures and waiving of testing 

Experience may have proven the corrosivity of given substances and mixtures. In such cases, 
no more testing is needed (see examples in Section 2.16.7). 

Generally  extreme  pH-values  point  to  a  higher  likelihood  that  the  substance  or  mixture  is 
corrosive. However, it cannot lead to immediate classification in the hazard class corrosive to 
metals. As a proof of that, Figure 2.15 shows that immunity zones (where steel does not corrode) 
still exist on the full spectrum of pH values as far as carbon steel is concerned. 

 
 
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Corrosivity is so complex that the evaluation of a mixture cannot be extrapolated from similar 
behaviour of constituents of a mixture. However, if one significant component of a mixture is 
corrosive  to  metals  the  mixture  is  likely  to  be  corrosive  to  metals  as  well.  Testing  the  actual 
mixture is therefore highly recommended. As already mentioned, solids are currently difficult to 
test according to the current CLP requirements, as the UN Test C.1 was designed for liquids. 

Where an initial test on either steel or aluminium indicates the substance or mixture being tested 
is corrosive, the follow up test on the other metal is not required. 

2.16.4.3.  Classification criteria 

Substances  and  mixtures  of  hazard  class  corrosive  to  metals  are  classified  in  a  single  hazard 
category on the basis of the outcome of the UN Test C.1 (UN-MTC, Part III, Section 37, paragraph 
37.4). 

Annex I: Table 2.16.1 

Criteria for substances and mixtures corrosive to metals 

Category 

Criteria 

1 

Corrosion rate on either steel or aluminium surfaces exceeding 6,25 mm per 
year at a test temperature of 55 °C when tested on both materials. 

2.16.4.4.  Testing and evaluation of hazard information 

2.16.4.4.1.  General considerations 

It is important to point out that the criteria of corrosion rate will never be applied in an absolute 
way,  but  by  extrapolating  the  measured  rate  of  corrosion  over  the  test  period  to  the  annual 
assumed  correlating  corrosion  rate.  This  exercise  has  to  take  account  of  the  fact  that  the 
corrosion  rate  is  not  necessarily  constant  over  time.  Expert  judgement  may  be  required  to 
consolidate the optimum test duration and to ascertain test results. However, the possibility of 
increasing the testing period from minimum one week to four weeks as well as the use of two 
different metals in the UN Test C.1 act as barriers against erroneous classification. 

Whatever the result of the classification may be, the classification as corrosive to metals relates 
to steel and/or aluminium only and does not provide information with regard to the corrosivity 
potential to other metals than those tested. 

Two types of corrosion phenomena need to be distinguished for classification of substances and 
mixtures in this hazard class, although not reported in CLP: the uniform corrosion attack and 
the localised corrosion (e.g. pitting corrosion, shallow pit corrosion). 

Table 2.3 (Section 37.4.1.4.1 of the UN-MTC) translates the corresponding minimum mass loss 
rates leading to classify the test substance or mixture as corrosive to metals for standard metal 
specimens (2 mm of thickness), according to time of exposure, for reasons of uniform corrosion 
process. In case of use of metal plates of a thickness that differs from the specified 2 mm (see 
comments in Section 2.16.4.2), the values in Tables 2.3 and 2.4 need adjustments due to the 
fact that the corrosion process depends on the surface of specimen. 

 
 
 
 
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Table 2.3 Minimum mass loss of specimens after different exposure times (corresponding to 
the criterion of 6.25 mm/year, correspond to Table 37.4.1.1 of UN-MTC) 

Exposure time (days) 

Mass loss (%) 

7 

14 

21 

28 

13.5 

26.5 

39.2 

51.5 

Table 2.4 (Section 37.4.1.4.2 of the UN-MTC) indicates the criteria leading to classification of 
the test substance or mixture as corrosive to metals for standard metal specimens, according to 
time of exposure, for reasons of localised corrosion process. 

Table 2.4 Minimum intrusion depths after exposure times (corresponding to the criterion of 
localised corrosion of 6.25 mm/year, correspond to Table 37.4.1.2 of UN-MTC) 

Exposure time (days) 

Min. intrusion depth (m) 

7 

14 

21 

28 

120 

240 

360 

480 

It is not mentioned explicitly in the text that localised corrosion as well as uniform corrosion has 
also been taken into account. However, localised corrosion, that is entirely part of the UN Test 
C.1  protocol,  has  to  be  taken  into  account.  In  addition,  although  the  type  of  corrosion  is  not 
reflected in the classification result, this valuable information should be given in the SDS. 

2.16.4.4.2.  Additional notes on best practice for testing 

Competence required for testing 

The overall evaluation of appropriate data for considering the corrosion properties of a substance 
or a mixture, in particular for testing according to the mentioned criteria for this hazard class, 
requires certain qualifications and experience. Expertise is often needed for this hazard class, 
which relates to a complex and multi-faceted hazardous phenomenon. 

Selection of metal specimens 

CLP refers to two types of metals (carbon steel and aluminium) meeting accurate specifications 
(technical  characteristics  of  metal  sheets  and  plate  thickness).  Thicker  metal  sheets,  such  as 
cast materials, of which the thickness is reduced to 2 mm by any form of mechanical treatment, 
may  never  be  used.  Mechanical  reduction  of  sheet  (metal)  thickness  could  induce  corrosion 
enhanced  process  due  to  cross  section  heterogeneity  in  metal  grain  and  impurities.  It  is  far 
better to use slightly different specifications of metal in the correct thickness or slightly different 
specimen  plate  thicknesses.  It  is  recognised  that  it  will  not  always  be  easy  to  obtain  metal 
specimens with the profile as described above. 

Regarding the type of aluminium or steel to be used for this test see UN-MTC, Section 37.4.1.2. 

Minimum corrosive media volume 

To prevent any limitation on the corrosion process due to full consumption of the corrosive media 
before the end of the testing period, a minimum volume of substance or mixture (1.5 L, according 

 
 
 
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to  the  UN-MTC)  has  to  be  used.  (Note:  volume/surface  ratio  of  10  mL/cm²  is  stated  in  DIN 
50905, similar in ASTM G31–72.) 

Adjustment of the test temperature  

Corrosion processes are temperature dependent. In the context of CLP, the property corrosive 
to metals is assessed through testing metal specimens at a specified temperature of 55 °C  1 
°C. In practice, it may be difficult with standard testing equipment to stay within the temperature 
window (55 °C  1 °C) of the gas phase, all over the test period. In such case, the test can be 
performed conservatively at a slightly higher temperature and somewhat lower accuracy (e.g. 
57 °C  3 °C). 

Selecting the appropriate test duration 

The  evaluation  of  the  criterion  of  6.25  mm/year  is  generally  based  on  a  test  duration  not 
exceeding 1 month. There is the option to stop the test procedure already after 1 week. For the 
decision on test duration, the non-linear behaviour of the corrosion process must be taken due 
account of. In borderline cases a non-appropriate test duration may result in either false positive 
or false negative results. 

Specimen cleaning 

Attention must be paid to the correct cleaning of the corroded residue before measurement of 
the  corrosion  characteristics.  In  case  of  adhesive  corroded  layer,  the  same  cleaning  process 
needs  to  be  carried  out  on  a  non-corroded  sample  to  verify  if  the  cleaning  procedure  is  not 
significantly abrasive. For further information see UN-MTC, section 37.4.1.3. 

Testing soluble solids 

As said in Section 2.16.4.4.2, for solids that may become liquids through dissolution in water or 
in a solvent, the adequate testing procedure is more complex (not explicitly described in the UN 
C.1 test protocol). In no case will simple dilution of the solid substance or mixture in any quantity 
of water lead to satisfactory testing of the substance or mixture for corrosion to metals. 

For the specific case where the  corrosion potential is linked to the presence  of solvent traces 
(other than water), expert judgement is needed to determine whether further testing must be 
performed (where the solid is put in interaction with the metallic part considered). 

Example of equipment relevant for the performance UN Test C.1 

 
 
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Figure 2.16 Example of testing equipment available on the market to perform UN Test C.1 

2.16.4.5.  Decision logic 

Classification of substances and mixtures corrosive to metals is done according to decision logics 
2.16.4.1 as included in GHS. 

NOTE: The person responsible for the classification of substances and mixtures corrosive to 
metals should be experienced in this field and be familiar with the criteria for classification. 

 
 
 
 
 
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Figure 2.17 Decision logic for substances and mixtures corrosive to metals (Decision logic 2.16 
of GHS) 

Substance/mixture 

Does it corrode either steel or aluminium surfaces at a rate 
exceeding 6.25 mm/year at a test temperature of 55 °C 
when tested on both materials? 

No 

Yes 

Not classified 

Category 1 

Warning 

2.16.5.  Hazard communication for corrosive to metals 

2.16.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

Table 2.16.2 of CLP Annex I provides the label elements for hazard class corrosive to metals. 
The  hazard  statement  H290,  using  the  wording  ‘may’,  reflects  that  classification  under  this 
hazard  class  does  not  cover  all  metals  (testing  only  considers  carbon  steel  and  aluminium). 
Consequently,  we  may  find  examples  of  substances  and  mixtures  that  are  classified  in  this 
hazard  class  corrosive  to  metals  but  will  not  induce  corrosive  action  on  other  more  corrosive 
resistant metals (e.g. platinum) than those serving as reference materials. 

Label elements must be used for substances and mixtures meeting the criteria for classification 
in this hazard class in accordance with Table 2.16.2. 

Annex I: 2.16.3. Table 2.16.2 

Label elements for substances and mixtures corrosive to metals 

Classification 

GHS Pictogram 

Category 1 

Signal Word 

Hazard Statement 

Warning 

H290: May be corrosive to metals 

Precautionary Statement, Prevention 

Precautionary Statement, Response 

P234 

P390 

 
 
 
 
 
 
  
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Precautionary Statement, Storage 

P406 

Precautionary Statement, Disposal 

Note:  

Where a substance or mixture is classified as corrosive to metals but not corrosive to skin 
and/or eyes, the labelling provisions set out in Section 1.3.6 shall be used. 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

Furthermore, CLP Annex I, section 1.3.6 provides a derogation from labelling requirements for 
substances or mixtures classified as corrosive to metals but not corrosive to skin and/or eyes. 

Annex I: 1.3.6 Substances or mixtures classified as corrosive to metals but not 
classified as skin corrosion or as serious eye damage (Category 1) 

Substances or mixtures classified as corrosive to metals but not classified as skin corrosion 
or as serious eye damage (Category 1) which are in the finished state as packaged for 
consumer use do not require on the label the hazard pictogram GHS05. 

2.16.6.  Relation to transport classification 

Class 8 of the UN RTDG Model Regulations covers substances and mixtures that are classified 
for corrosivity to skin, metals or both. Valuable information can be obtained from the UN RTDG 
Model Regulations and the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO 
TI). Existing test results obtained in the context of the modal transport regulations (ADR, RID, 
ADN and IMDG Code, ICAO TI) may be applied since the UN Test C.1 serves as reference for 
testing  in  both  classification  systems.  See  Annex  I  for  additional  information  on  transport 
classification in relation to CLP classification. 

2.16.7.  Example of classification for corrosive to metals 

The following table lists some examples of substances and mixtures that should be classified, 
or not, in Class 2.16 (according to known UN Test C.1 results) in comparison with predicted 
results for skin corrosion hazard. 

Table 2.5 Examples of classified and non-classified substances and mixtures in Class 2.16 

Substance or mixture 

Steel 

Aluminium  CLP Annex I, 2.16 

classification 

Skin (for 
comparison) 

Hydrofluoric acid 

Not corroded  Corroded 

Classified 

Positive 

> 70 % (UN1790) 

Highly concentrated nitric 
acid (97 %) (UN2031) 

Not corroded  Corroded 

Classified 

Positive 

HNO3 red fuming (UN2032)  Not corroded  Not corroded  Not classified 

Positive 

Hydrochloric acid (diluted) 
(UN1789) 

Corroded 

Corroded 

Classified 

Negative 

NaOH solutions (UN1824) 

Not corroded  Corroded 

Classified 

Positive 

Note:  
the sense of UN Test C.1; ‘Positive’ or ‘Negative’ are results from skin corrosion. 

‘Corroded’ means corrosion attack in the sense of UN Test C.1; ‘Not corroded’ means corrosion resistant in 

 
 
 
 
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2.16.7.1.  Example of metal specimen plates after exposure to a corrosive 
mixture 

Figure 2.18 Example of corroded metal plates after testing according to UN Test C.1 for a 
classified mixture 

Plate located in the 
liquid phase 

Plate located in the 
interface 

Plate located in the 
vapour phase 

This example shows that the corrosion may develop at different rates according to the accurate 
position of the specimen related to the corroding mixture (sunk in the liquid, placed in the gas 
phase above liquid or at the liquid/gas interface). 

2.16.8.  References 

ASTM G31-72(2004) Standard Practice for Laboratory Immersion Corrosion Testing of Metals.  

Jones,  D.A.,  Principles  and  Prevention  of  Corrosion,  2nd  edition,  1996,  Prentice  Hall,  Upper 
Saddle River, NJ. ISBN 0-13-359993-0 Page 50-52. 

DIN  50905-1:  2007,  Corrosion  of  metals  -  Corrosion  testing  –  Part  1:  General  guidance 
(Korrosion der Metalle - Korrosionsuntersuchungen - Teil 1: Grundsätze). 

 
 
 
 
 
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2.17. DESENSITISED EXPLOSIVES 

2.17.1.  Introduction 

Desensitised explosives are covered in CLP Annex I, section 2.17. As the definition implies, they 
are derived from explosive substances and mixtures (see CLP Annex I, section 2.1.1.1(a) and 
(c)).  However,  desensitisation  of  explosive  articles  (CLP  Annex  I,  section  2.1.1.1(b))  is  not 
possible. 

The  desensitisation  is  achieved  on  the  one  hand  by  a  dilution  effect  (reduction  of  the 
decomposition energy), on the other hand by disruption of the propagation of a shock wave in 
combination with an energy-absorbing endothermic evaporation. 

As the definition implies, desensitised explosives are generally mixtures consisting of the original 
explosive substance or mixture and the phlegmatiser or diluent. However, if the phlegmatiser is 
built directly into the crystal lattice and is therefore chemically bonded (see note in CLP Annex 
I, section 2.17.1.2(a)), such desensitised explosive would be not a mixture but a substance. 

For the “regular” desensitised explosives it is essential that the original explosive and the diluent 
are HOMOGENEOUSLY mixed. For a solvent-based solid desensitised explosive this means that 
the diluent has to be evenly distributed among the crystals and not form a wet suspension in 
the lower part of a package with dry material on the top. Therefore, at least a sufficient amount 
of liquid has to remain between the crystals to function effectively as desensitiser; separation of 
excess material is tolerable. For desensitised explosives where a solid phlegmatiser is added to 
the  explosive  one  has  to  make  sure  that  the  components  are  permanently  homogeneously 
mixed.  This  is  usually  the  case  if  the  components  have  similar  crystal  sizes  and  comparable 
densities. See also note 1 in section 2.17.4.3. 

2.17.2.  Definitions and general considerations for desensitised explosives 

CLP  comprises  the  following  definition  for  substances  and  mixtures  that  are  desensitised 
explosives. 

Annex I: 2.17.1.1     Definition 

Desensitised explosives are solid or liquid explosive substances or mixtures which are 
phlegmatised to suppress their explosive properties in such a manner that they do not mass 
explode and do not burn too rapidly and therefore may be exempted from the hazard class 
‘Explosives’ (see also paragraph 3 in section 2.1.4.1) (1)  

2.17.1.2. The hazard class of desensitised explosives comprises: 

(a) Solid desensitised explosives: explosive substances or mixtures, which are wetted 
with water or alcohols or are diluted with other substances, to form a homogeneous solid 
mixture to suppress their explosive properties. 

NOTE: This includes desensitisation achieved by formation of hydrates of the substances. 

(b) Liquid desensitised explosives: explosive substances or mixtures, which are dissolved 
or suspended in water or other liquid substances, to form a homogeneous liquid mixture 
to suppress their explosive properties. 

(1)  Unstable explosives as defined in Section 2.1 can also be stabilised by desensitisation and 
consequently may be classified as desensitised explosives, provided all criteria of Section 
2.17 are met. In this case the desensitised explosive shall be tested according to test 
series 3 (Part I of the UN RTDG, Manual of Tests and Criteria) because information about 
its sensitiveness to mechanical stimuli is likely to be important for determining conditions 
for safe handling and use. The results shall be communicated in the safety data sheet. 

 
 
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2.17.3.  Relation to other physical hazards 

The only possibility to “enter” the class of desensitised explosives is from the class of explosives 
(section 0) by dilution or phlegmatisation. 

Classification as explosive and desensitised explosive are mutually exclusive. Further, note 3 in 
CLP Annex I, Table 2.17.1 explicitly states that “desensitised explosives do not fall additionally 
within the scope of sections […] 2.6 (flammable liquids) and 2.7 (flammable solids).” 

Explosives  may  sometimes  be  an  active  ingredient  in  aerosols,  specifically  used  for  medical 
purposes  (i.e.  nitroglycerin  spray  for  treatment  of  heart  emergencies).  However,  the 
concentration is usually so small that the respective aerosol is neither classified as explosive nor 
as desensitised  explosive, because the decomposition energy will fall  below the lower limit of 
300 J/g of CLP 2.17.2.1(c), so that classification as desensitised explosive does not apply. 

Since  desensitised  explosives  are  by  definition  explosives  that  have  been  phlegmatised,  they 
cannot be self-reactive substances and mixtures according to CLP Annex I, section 2.8.2.1(a). 
By  definition  in  CLP  Annex  I,  section  2.15.1.1,  organic  peroxides  cannot  be  classified  as 
desensitised explosives.   

Generally, desensitised explosives will not be classified as oxidising solids or liquids, respectively. 
It is advisable to also check the chapter about explosives in this guidance. 

Although a simultaneous classification as pyrophoric solid / liquid (sections 2.9 and 2.10), self-
heating (section 2.11) or water-reactive (section 2.12) cannot be precluded, such combination 
would be applicable  only in extremely rare cases where the resulting intrinsic increase of  risk 
has been intentionally accepted or designed. Substances and mixtures of these chapters usually 
consist  of chemicals that are reactive towards air or water whereas explosives have a certain 
decomposition energy stored as potential energy in the molecule or mixture that can be released. 

In rare cases, desensitised explosives may also be corrosive to metals (section 2.16). However, 
one  has  to  be  aware  that  metals  used  in  test  method  UN  C.1  of  the  UN-MTC  may  trigger 
decomposition. Therefore, it may not be possible to perform this test. In case of doubt, expert 
judgement should be applied. 

2.17.4.  Classification of substances and mixtures as desensitised explosives 

Annex I: 

2.17.2.1. Any explosive while in a desensitised state shall be considered in this class unless, in 
that state: 

(a) It is intended to produce a practical explosive or pyrotechnic effect; 

(b) It has a mass explosion hazard according to test series 6 (a) or 6 (b) or the corrected 
burning rate according to the burning rate test described in part V, subsection 51.4 of the UN 
RTDG, Manual of Tests and Criteria is greater than 1 200 kg/min; or 

(c) The exothermic decomposition energy is less than 300 J/g. 

NOTE 1: Substances or mixtures, which meet the criterion (a) or (b) in their desensitised 
state shall be classified as explosives (see Section 2.1). Substances or mixtures which meet 
the criterion (c) may fall within the scope of other physical hazard classes. 

NOTE 2: The exothermic decomposition energy may be estimated using a suitable calorimetric 
technique (see section 20, sub-section 20.3.3.3 in Part II of the UN RTDG, Manual of Tests 
and Criteria). 

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1.  Is the “original” substance or mixture (= substance or mixture before desensitisation) an 
explosive as defined in section 2.1? If not, a classification as desensitised explosive is not 
applicable. 

2.  Is  the  substance  or  mixture  in  the  desensitised  form  intended  to  produce  a  practical 

explosive or pyrotechnic effect? If yes, it remains in the class of explosives. 

3.  Does the diluent or phlegmatiser fulfil the intended function, especially with respect to a 
permanent homogeneous distribution (see explanations in section 2.17.1 above)? If not, 
a classification as desensitised explosive is not possible. 

4.  What is the value of exothermic decomposition energy? If the answer is less than 300 
J/g,  the  class  of  desensitised  explosives  is  not  applicable;  in  this  case,  potential 
classification as flammable liquids or flammable solids should be checked. 

5.  Is the phlegmatised explosive too sensitive or thermally unstable in accordance with Test 
Series 3 of the UN-MTC? If yes, such mixture will remain an explosive of class 2.1. Where 
a  mixture  contains  nitrocellulose,  additional  data  of  the  nitrocellulose  as  described  in 
Appendix 10 of the UN-MTC are needed to be used in nitrocellulose mixtures considered 
in this class. 

Subsequently, testing is required: 

Test 6 (a) and 6 (b) according to sections 16.4 and 16.5 of the UN-MTC should be performed to 
establish that the intended desensitised explosive has no mass explosion hazard. 

Alternatively, Test Series 2 according to Part I, section 2 of the UN-MTC may be performed with 
the phlegmatised explosive. If a negative result (“-”) is obtained in each of the three individual 
tests,  it  is  “too  insensitive  for  inclusion  in  the  class  of  explosives”  and  thus  may  qualify  for 
classification  as  a  desensitised  explosive.  In  this  case,  Test  6  (a)  and  6  (b)  need  not  be 
performed. 

Finally, the burning rate test of section 51.4 of the UN-MTC will confirm the classification as a 
desensitised  explosive  and  lead  to  the  assignment  of  the  category.  However,  if  the  corrected 
burning rate is found to be 1200 kg/min or more, such material is moved back to the class of 
explosives.  

2.17.4.1. 

Identification of hazard information 

Since desensitised explosives are derived from explosives it is advisable to gather information 
about these properties first. In a second step, the diluent or phlegmatiser should be checked; 
key requirements are: 

•  The diluent (phlegmatiser) has to be chemically inert towards the explosive. This means that 
this compound does not interact with the explosive in any way that would reduce the thermal 
or chemical stability. 

•  Further,  the  diluent  must  be  effective  in  its  function  as  a  desensitiser  (see  also  section 
2.17.1)  with  a  homogeneous  distribution  over  extended  periods  of  time  (i.e.  duration  of 
storage). 

2.17.4.2.  Screening procedures and waiving of testing 

The screening procedures for explosives are described in section 2.1.4.2. 

Phlegmatised mixtures with a decomposition energy below 300 J/g should not be classified as 
desensitised explosive (see CLP Annex I, section 2.17.2.1(c)). 

2.17.4.3.  Classification criteria 

Substances  and  mixtures  of  hazard  class  desensitised  explosives  are  classified  in  four  hazard 
categories on the basis of the corrected burning rate (UN-MTC, section 51.4), according to CLP 
Annex I, Table 2.17.1. 

 
 
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Annex I: Table 2.17.1 

Criteria for desensitised explosives 

Category 

Criteria 

1 

2 

3 

4 

Desensitised explosives with a corrected burning rate (AC) equal to or greater 
than 300 kg/min but not more than 1 200 kg/min 

Desensitised explosives with a corrected burning rate (AC) equal to or greater 
than 140 kg/min but less than 300 kg/min 

Desensitised explosives with a corrected burning rate (AC) equal to or greater 
than 60 kg/min but less than 140 kg/min 

Desensitised explosives with a corrected burning rate (AC) less than 60 kg/min 

Note 1: Desensitised explosives shall be prepared so that they remain homogeneous and do 
not separate during normal storage and handling, particularly if desensitised by wetting. The 
manufacturer/supplier shall give information in the safety data sheet about the shelf-life and 
instructions on verifying desensitisation. Under certain conditions the content of desensitising 
agent (e.g. phlegmatiser, wetting agent or treatment) may decrease during supply and use, 
and thus, the hazard potential of the desensitised explosive may increase. In addition, the 
safety data sheet shall include advice on avoiding increased fire, blast or projection hazards 
when the substance or mixture is not sufficiently desensitised. 

Note 2: Explosive properties of desensitised explosives shall be determined by test series 2 of 
the UN RTDG, Manual of Tests and Criteria, and shall be communicated in the safety data 
sheet. 

Note 3: For the purposes of storage, supply and use, desensitised explosives do not fall 
additionally within the scope of Sections 2.1 (explosives), 2.6 (flammable liquids) and 2.7 
(flammable solids). 

2.17.4.4.  Testing and evaluation of hazard information 

General considerations 

Due  to  the  high  risks  relating  to  the  handling  of  explosives,  the  testing  personnel  should  be 
sufficiently qualified and experienced in performing the  required tests. Please  refer to section 
2.1.4.4 for further details.  

Additional notes on best practice for testing 

Before applying the desensitiser, the explosive properties of the “original” substance or mixture 
should be known (in general: results of Test Series 2, 3 (a) and 3 (b) of the UN-MTC; further 
data  about  thermal  stability  such  as  Test  3  (c),  or  appropriate  data  determined  according  to 
section 20.3.3.3 of the UN-MTC or data from application of microcalorimetric methods). 

Subsequently, the effect of the diluent/phlegmatiser should be examined; see section 2.17.1. 

2.17.4.5.  Decision logic  

Classification of substances or mixtures as desensitised explosives is done according to decision 
logics in CLP Annex I, Figure 2.17.1. 

NOTE: The person responsible for desensitised explosives should be experienced in this 
field and be familiar with the criteria for classification. 

 
 
 
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Annex I: Figure 2.17.1  Desensitised explosives 

Substance/mixture is solid or liquid? 

Does it contain an explosive substance or mixture which is phlegmatized 
to suppress the explosive properties? 

Is the exothermic decomposition energy less than 300 J/g? 

Yes 

No 

Test 6 (a), 6 (b): Is the result a mass explosion? 

No 

Burning rate test (Part V, sub-section 51.4): 

Is the result a mass explosion? 

No 

Ac > 1200 kg/min? 

No 

Ac ≥ 300 kg/min but < 1200 kg/min? 

No 

Ac ≥ 140 kg/min but < 300 kg/min? 

No 

Ac ≥ 60 kg/min but < 140 kg/min? 

No 

Ac < 60 kg/min? 

No 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Yes 

Not classified as a 
desensitized explosive 

May fall within the scope of 
other physical hazard 
classes 

Explosive 
Division 1.1 

Danger 

Hazard class “Explosives” 
(see criteria in 
Chapter 2.1) 

Category 1 

Danger 

Category 2 

Danger 

Category 3 

Warning 

Category 4 

Warning 

 
 
 
 
 
 
 
 
 
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2.17.5.  Hazard communication for desensitised explosives 

2.17.5.1.  Pictograms, signal words, hazard statements and precautionary 
statements 

Table 2.17.2 of CLP Annex I provides the label elements for hazard class desensitised explosives. 

Label elements must be used for substances and mixtures meeting the criteria for classification 
in this hazard class in accordance with Table 2.17.2. 

Annex I: 2.16.3. Table 2.17.2 Label elements for desensitised explosives 

Classification 

Category 1 

Category 2 

Category 3 

Category 4 

GHS Pictogram 

Signal Word 

Danger 

Danger 

Warning 

Warning 

H206 Fire, blast or 
projection hazard; 
increase risk of 
explosion if 
desensitising agent is 
reduced 

H207 Fire or 
projection hazard; 
increased risk of 
explosion if 
desensitising agent is 
reduced 

H207 Fire or 
projection hazard; 
increased risk of 
explosion if 
desensitising agent is 
reduced 

H208 Fire hazard; 
increased risk of 
explosion if 
desensitising agent is 
reduced 

P210 

P212 

P230 

P233 

P280 

P210 

P212 

P230 

P233 

P280 

P210 

P212 

P230 

P233 

P280 

P210 

P212 

P230 

P233 

P280 

P370 + P380+ P375 

P370 + P380+ P375 

P370 + P380+ P375 

P371 + P380+ P375 

P401 

P401 

P401 

P401 

P501 

P501 

P501 

P501 

Hazard 
Statement 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Storage 

Precautionary 
Statement 
Disposal 

The wording of the precautionary statements is found in CLP Annex IV, Part 2. 

2.17.6.  Relation to transport classification 

Since desensitised explosives have a high rank in the precedence tables of the Dangerous Goods 
Regulations,  such  substances  and  mixtures  will  be  classified  likewise  in  CLP.  Unlike  in  CLP, 
desensitised  explosives  are  not  a  hazard  class  of  their  own  for  transport.  Instead,  such 
substances  and  mixtures  are  transported  under  specific  UN-numbers  in  class  3  (liquids)  or 
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2.17.7.  Examples of classification for desensitised explosives 

A detailed example for the classification of a new substance as a desensitised explosive can be 
found on the UN website using the following link: ST/SG/AC.10/C.3/2021/32 (unece.org). 

This  document  describes  in  detail  testing  that  has  been  performed  for  the  original  explosive 
substance, and subsequently the test results in the desensitised form up to the assignment of a 
category.

 
 
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ANNEX I: RELATION BETWEEN TRANSPORT AND CLP 
CLASSIFICATION REGARDING PHYSICAL HAZARDS 

Table  I.1  on  physical  hazards  only,  provided  in  this  annex,  contains  additional  information  on 
transport classifications in relation to CLP classifications that could be of added value. However, 
these comparisons have  certain restrictions with regard to their applicability. In particular, the 
area  of  applicability  of  the  transport  regulation  is  different  from  the  CLP  Regulation  (ADR  49 
countries, IMDG-Code, ICAO-TI international regulations). Therefore, the table should be used as 
reference for deriving CLP classifications and not vice versa. 

The transport classification of named substances or mixtures in the transport regulations reflects 
the transport conditions and therefore were not adapted to take into account the GHS criteria. 
The transport classifications may be based on  experience  or certain  events that are specific to 
transport.  The  transport  classification  of  named  substances  or  mixtures  is  legally  binding  for 
transport and should not be used to derive a CLP classification without an expert review. 

The  transport  regulations  include  the  concept  of  precedence  of  hazards  which  guarantees  that 
information on the most dangerous hazards is communicated with precedence. CLP does not apply 
a  precedence  of  hazards  and  therefore  substances  or  mixtures  might  need  to  be  classified  in 
additional hazard classes under CLP, which in the transport classification are allocated and noted 
under the respective UN-Number (giving information on subsidiary risks, appropriate packaging 
and transport conditions). 

It needs to be noted that a substance may have more than one entry in the Dangerous Goods 
List. These are usually within the same class, but transport conditions are different because of 
different severity of the hazard for different concentrations of this substance. 

The  following  table  refers  only  to  physical  hazards,  as  health  hazards  are  not  harmonised 
regarding cut-off values, and/or allowed methods. 

Table I.1  Relation between transport and CLP classifications regarding physical hazards 

  (NOTE that within transport, the term ‘substances’ covers also mixtures in CLP terms.) 

Transport classification 

Physical 
state 

CLP-classification 

Remarks 

Transport 
class and 
(sub)division 
(if 
applicable) 

Packing group, 
division, type, 
group or code 

Class 1 

Division 1.1 

Division 1.2 

Division 1.3 

Division 1.4 

Division 1.5 

Division 1.6 

Liquid or 
solid 

Hazard 
category, 
division, 
type or 
group 

Hazard class 

Explosives 

Division 1.1 

Matching criteria. 

Division 1.2 

Division 1.3 

Division 1.4 

Division 1.5 

Division 1.6 

However, if 
explosives are un-
packed or repacked, 
they have to be 
assigned to division 
1.1 unless the 
hazard is shown to 
correspond to one of 
the other divisions. 

 
 
 
 
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Class 2*  

– Gases 

1 Compressed 
gas 

Gaseous 

Gases under 
pressure 

Compressed 
gas 

2 Liquefied gas   Gaseous 

Liquefied gas  

3 Refrigerated 
liquefied gas 

Gaseous 

Refrigerated 
liquefied gas 

4 Dissolved gas 

Gaseous 

Dissolved gas 

A correspondence 
only applies to the 
form in which the 
gas is transported. If 
it is used in a 
different form, then 
the classification has 
to be amended. 

Matching criteria 
with 2.5. Note: 
Gases may be 
packaged in other 
forms such as 
“chemical under 
pressure” or 
“adsorbed gases” 
that are not 
considered in the 
GHS/CLP. 

The transport 
classification does 
not differentiate 
between Aerosols 
Category 1 and 2 
(both are classified 
as class 2.1)  

5 Aerosol 
dispensers,  

Class 2.1 

Class 2.2 

6 Other articles 
containing gas 
under pressure 

7 Non-
pressurised 
gases subject to 
special 
requirements  

8 Chemicals 
under 
pressure*** 

Not 
relevant 

(Articles)  

Aerosols 

Category 1 

Category 2 

Category 3 

Gaseous 

Flammable 
gases 

Category 1 

Gaseous 

Oxidising 
gases 

Category 1 

Not 
relevant 

9 Adsorbed gas 

Gaseous 

Class 3 

Packing group I 

Liquid 

Packing group II 

Liquid 

Packing group 
III 

Liquid 

Flammable 
liquid 

Flammable 
liquid 

Flammable 
liquid 

Category 1 

Category 2 

Category 3 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Class 4.1 

Types B-F 

Solid or 
liquid 

Self-reactive 
substances 

Types B-F 

Class 4.1 
(solid 
desensitized 
explosives) 

Class 4.1 
(only readily 
combustible 
solids) 

Class 4.1 
(only readily 
combustible 
solids) 

Class 4.2 

Pyrophoric 
substances 

Packing group I 

Solid 

Solid 
desensitized 
explosives 

Packing group II  Solid 

Flammable 
solids 

Category 1 

Packing group 
III 

Solid 

Flammable 
solids 

Category 2 

Packing group I 

Liquid 

Solid 

Class 4.2  

Packing group II  Solid 

Class 4.2 

Packing group 
III 

Solid 

Class 4.3 

Packing group I 

Packing group II 

Packing group 
III 

Liquid or 
solid 

Pyrophoric 
liquids 

Pyrophoric 
solids 

Self-heating 
substances 
and mixtures 

Self-heating 
substances 
and mixtures 

Substances 
which in 
contact with 
water emit 
flammable 
gases 

Category 1 

Category 1 

Category 1 

Category 2 

Category 1 

Category 2 

Category 3 

Class 5.1 

Packing group I 

Solid  

Oxidising solid  Category 1 

Packing group II 

Packing group 
III 

Class 5.1 

Packing group I 

Liquid 

Packing group II 

Packing group 
III 

Oxidising 
liquid 

Category 2 

Category 3 

Category 1 

Category 2 

Category 3 

Class 5.2  

Types B-F 

Solid or 
liquid 

Organic 
peroxides 

Types B-F 

Class 8 

Packing group 
III 

Liquid or 
solid 

Corrosive to 
metals  

Category 1 

Applies only when 
the substance or 
mixture is not 
classified as 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
176 

Version 4.0 – Nov 2024 

Guidance on the Application of the CLP Criteria, Part 2 

corrosive to skin 
and/or eye. 

(*) Substances and articles (except aerosols and chemicals under pressure) of Class 2 are assigned to one of 
the following transport groups according to their hazardous properties, as follows: An asphyxiant, O oxidising, 
F  flammable,  T  toxic,  TF  toxic,  flammable,  TC  toxic  corrosive,  TO  toxic,  oxidising,  TFC  toxic,  flammable, 
corrosive, TOC toxic, oxidising, corrosive 

(**) Aerosols are assigned to one of the following transport groups according to their hazardous properties, as 
follows: An asphyxiant, O oxidising, F flammable, T toxic, C corrosive, CO corrosive, oxidising, FC flammable, 
corrosive, TF toxic, flammable, TC toxic corrosive,  TO toxic, oxidising, TFC toxic, flammable, corrosive, TOC 
toxic, oxidising, corrosive 

(***)  Chemicals  under  pressure  are  assigned  to  one  of  the  following  transport  groups  according  to  their 
hazardous properties, as follows: An asphyxiant, F flammable, T toxic, C corrosive, FC flammable, corrosive, 
TF toxic, flammable

 
 
 
EUROPEAN CHEMICALS AGENCY 
P.O. BOX 400,  
ECHA.EUROPA.EU