DRAFT UGANDA STANDARD  
  DUS 761  
Second Edition  
2017 -may-dd 
 
 
 Reference number  
WDUS 761: 2017  
© UNBS 2017   
  
Biomass stoves  — Requirements  
 DUS 761: 2017  
ii © UNBS 2017  – All rights reserved  
 Compliance with this standard does not, of itself confer immunity from legal obligations  
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct applicatio n 
© UNBS 2017   
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, including photocopying and microfilm, without prior written 
permission from UNB S. 
Requests for permission to reproduce this document should be addressed to  
The Executive Director  
Uganda National Bureau of Standards  
P.O. Box 6329  
Kampala  
Uganda  
Tel: +256 41 4 333 2 50/1/2/3  
Fax: +256 41 4 286 123  
E-mail: info@unbs.go.ug  
Web: www.unbs.go.ug  DUS 761:2017  
© UNB S 2017  – All rights reserved  iii 
 Contents   Page 
Foreword  ................................ ................................ ................................ ................................ .............................  v 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Classification  ................................ ................................ ................................ ................................ .........  2 
5 Technical requirements  ................................ ................................ ................................ ........................  2 
5.1 Basic requirements  ................................ ................................ ................................ ...............................  2 
5.2 Manufactu ring requirement s ................................ ................................ ................................ ................  3 
5.3 Performance requirements  ................................ ................................ ................................ ...................  3 
6 Safety requirements  ................................ ................................ ................................ ..............................  3 
7 Durability requirements  ................................ ................................ ................................ ........................  4 
8 Tests for cookstoves ................................ ................................ ................................ .............................  4 
8.1 Manufacturer/supplier description  ................................ ................................ ................................ ...... 4 
8.3 Test procedures  ................................ ................................ ................................ ................................ ..... 4 
9. User instructions and safety precautions ................................ ................................ ...........................  4 
10 Marking and packa ging ................................ ................................ ................................ .........................  5 
10.1  Marking  ................................ ................................ ................................ ................................ ...................  5 
10.2  Packaging  ................................ ................................ ................................ ................................ ...............  5 
Annex A (normative)    Test report  ................................ ................................ ................................ ....................  6 
Annex B (normative)    Thermal performance tests  ................................ ................................ .........................  7 
B.1 Thermal performance test  ................................ ................................ ................................ ....................  7 
B.1.1  Test equipment and instruments  ................................ ................................ ................................ .........  7 
B.1.2  Pot size and water quantity  ................................ ................................ ................................ ..................  7 
B.2 Test conditions  ................................ ................................ ................................ ................................ ...... 7 
B.3 Test preparation  ................................ ................................ ................................ ................................ .... 7 
B.4 Test steps  ................................ ................................ ................................ ................................ ...............  8 
B.5 Calculation  ................................ ................................ ................................ ................................ .............  8 
B.5.1  Useful energy  ................................ ................................ ................................ ................................ .........  8 
B.5.2  Cooking power  ................................ ................................ ................................ ................................ ....... 8 
B.5.3  Cooking thermal efficie ncy ................................ ................................ ................................ ..................  9 
Annex C (normative)    Emissions tests  ................................ ................................ ................................ ..........  10 
C.1 Emission measurements of PM 2.5 and CO  ................................ ................................ ........................  10 
C.1.1  Test preparation  ................................ ................................ ................................ ................................ .. 10 
Figure C.2 — Hood and dilution tunnel apparatus  for collecting emissions from cookstoves 
without chimneys  ................................ ................................ ................................ ................................  12 
C.1.2  Test method  ................................ ................................ ................................ ................................ .........  12 
C.1.3  Test steps  ................................ ................................ ................................ ................................ .............  13 
C.2 Calculation of Emission Factors  ................................ ................................ ................................ ........  14 
C.2.1  PM 2.5 ................................ ................................ ................................ ................................ ......................  14 
C.2.2  CO ................................ ................................ ................................ ................................ .........................  14 
C.3 Testing repeats  ................................ ................................ ................................ ................................ .... 14 
Annex D (normative)    safety tests and scoring tables  ................................ ................................ ................  15 
D.1 Safety tests  ................................ ................................ ................................ ................................ ..........  15 
D.1.1  Sharp e dges and points test  ................................ ................................ ................................ ..............  15 
D.1.2  Cookstove tipping test  ................................ ................................ ................................ ........................  15 DUS 761: 2017  
iv © UNBS 2017  – All rights reserved  
 D.1.3  Containment of fuel test  ................................ ................................ ................................ .....................  17 
D.1.4  Obstructions near cooking surface test  ................................ ................................ ...........................  18 
D.1.5  Surface temperature test  ................................ ................................ ................................ ...................  19 
D.1.6  Heat transfer to the environment test  ................................ ................................ ...............................  19 
D.1.7  Handle temperature test  ................................ ................................ ................................ .....................  21 
D.1.8  Chimney test  ................................ ................................ ................................ ................................ ....... 22 
D.1.9  Flames surrounding cooking vessel test  ................................ ................................ .........................  22 
D.1.10  Flames exiting fuel chamber test  ................................ ................................ ................................ ...... 22 
D.1.11  Overall safe ty score  ................................ ................................ ................................ ............................  23 
Annex E (normative)    Durability tests and scoring  ................................ ................................ .....................  24 
E.1 Durability tests  ................................ ................................ ................................ ................................ .... 24 
E.1.1  Visual examination  after thermal performance and safety  tests  ................................ ...................  24 
E.1.2  Quenching test  ................................ ................................ ................................ ................................ .... 24 
E.1.2.4  Overall durability score  ................................ ................................ ................................ ......................  25 
Annex F (normative)    Features for visual inspection  ................................ ................................ ..................  26 
Bibliography  ................................ ................................ ................................ ................................ .....................  27 
 DUS 761:2017  
© UNB S 2017  – All rights reserved  v 
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry of Trade , Industry and 
Cooperatives established under Cap 327 , of the Laws of Uganda , as amended .  UNBS is mandated to co -
ordinate the elaboration of standards and  is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex Alimentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT  Agreement  of the World Trade Organisation (WTO).  
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a given field or area and consists of key stakeholders 
including government, academia, consumer groups, private secto r and other interested parties.  
Draft Uganda Standards adopted by the Technical Committee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval an d declaration as Uganda Standards by the National Standards Council.  
The committee responsible for this document is Technical Committee UNBS/TC 4, Mecha nical Engineering 
and Metallurgy . 
This second  edition cancels and replaces the first  edition ( US 761:2007), which has been technically revised.  
 DRAFT UGANDA STANDARD  DUS 761: 2017  
 
© UNBS 2017  – All rights reserved  1 
 Biomass stoves  — Requirements  
1 Scope   
This Draft Uganda standard specifies the classification , technical requirements, performance requirements 
safety requirements, test methods and inspection procedure of biomass  cookstoves.  
This draft standard is applicable to cookstoves using  solid biomass in its natural or densified  form. 
2 Normative references   
The following referenced documents referred to in the text in such a way that some or all of their content 
constitute s requirements of this document. For dated references, only the edition cited applies. For undated 
references, the latest edition of the referenced document (including any amendments) applies.  
ISO 18125 , Solid biofuels — Determination of calorific value  
ISO 4224 , Ambient air — Determination of carbon monoxide — Non-dispersive infrared spectrometric method  
ISO 25597 , Stationary source emissions — Test method for determining PM 2.5 and PM 10 mass in stack gases 
using cyclone samplers and sample dilution  
ISO 909 6, Stationary source emissions — Manual determination of mass concentration of particulate matter  
ISO 12039 , Stationary source emissions — Determination of carbon monoxide, carbon dioxide and oxygen — 
Performance characteristics and calibration of automate d measuring systems  
3 Terms and definitions   
For the purposes of this document, the following terms and definitions apply.  
3.1 
biomass cookstove  
stoves with cooking function, burning solid biomass  in its natural or densified form 
3.2 
densified biomass  
solid biomass  made by mechanically compressing  biomass  or thermally treated biomass into a specific size 
and shape such as cubes, pressed logs,  pellets  or  briquettes  
3.3 
useful energy  
energy absorbed by the water in the pot including the energy that raises the temperature and that evaporates 
water from the pot during the test  DUS 761: 2017  
2 © UNBS 2017  – All rights reserved  
 3.4 
cooking power  
useful energy per unit time.  
3.5 
cooking thermal efficiency  
the ratio of useful energy to the energy of fuel consumed.  
3.6 
emission factor  
the ratio of the mass of a pollutant emitted to the energy  of fuel consumed   
3.7 
PM 2.5 
particulate matter with an aerodynamic diameter of less than or equal to a nominal 2.5 µm, as determined in 
Annex C  
3.8 
Energy of fuel consumed  
amount of heat released during the combustion o f a specified amount of biomass  
ISO and IEC maintain terminological databases for use in standardization at the following addresses:  
— ISO Online browsing platform: available at http://www.iso.org/obp  
4 Classification  
Biomass stoves shall be classified as W-XX-Y, where :  
a) W represents of fuel type (for example C for charcoal, B for briquettes, a mong others ); 
b) XX represents nominal cooking power of the stove, kW; and   
c) Y specifies class  in accordance with Table 1 . 
Table 1 — Performance indicators of biomass s toves  
Class  Efficiency , 
ηc  
%  Emission  factor  Safety   
% Durability  
% PM 2.5  
mg/MJ  CO  
g/MJ  
Class 1  ＞50 ＜60 ＜5 ≥95 ≥94 
Class 2  41 - 50  60 - 99 5 - 8  76-94 80 - 93 
Class 3  30 - 40   100 - 250  8 - 12  ≥75 70 - 79 
NOTE  The values are determin ed in a ccordance with the test methods in the annexes  (Annex 
D for safety and Annex E for durability) . These values should be corrected to nearest whole 
number.  
 
 
5 Technical requirements  
5.1 Basic requirements  
The stove shall have good finish  without b urrs (rough or sharp edges)  or rust outside.  DUS 761: 2017  
© UNBS 2017  – All rights reserved  3 
 5.2 Manufacturing requirement s 
5.2.1  The stove or any of its parts may be manufactured using different material s and /or method s. 
5.2.2 Castings shall  have  a good finish and without cracks, stomata  (holes)  and s and holes.  
5.2.3 Weldments shall be flat and uniform without perforations and slag stomata.  
5.2.4 Stamped parts have  a good finish without cracks, wrinkles, flashes and burrs.  
5.2.5 Sheet metal surfaces and edges shall have  a good finish  without cracks, wr inkles, bumps and any 
type of imperfection.  
5.2.6 Riveted pieces shall be firmly attached and the rivets shall not be loose and /or skewed. Rivet heads 
shall be smooth and shall not protrude.  
5.2.7 Ceramic parts shall have  a good finish without cracks and v oids.  
5.2.8 For stoves made of different  parts such as ceramic core and a metal cladding, the parts shall be 
firmly assembled.  
5.3 Performance requirements   
5.3.1  The cooking power shall not be less than the stove nominal value  when tested in accordance with 
Annex B . 
5.3.2  The stove shall have a minimum efficiency of 30 %, maximum PM 2.5 of 250  mg/MJ , maximum CO 
emission level of 12  g/MJ, minimum safety of 75  % and minimum durability of 70  %. 
6 Safety requirements  
6.1 When the stove is in use, the surface t emperature shall be less than 60  ℃ when tested in accordance 
Annex D . 
6.2 The stove shall be stable on a flat surface and shall score a minimum of 0.94 when tested in 
accordance with D.1.2. 
6.3 Surfaces which in normal use have to be touched for short peri ods e.g. handles , the difference between 
maximum temperature and air temperature  shall not  exceed 38 ℃ when tested in ac cordance with Annex 
D.1.7. 
6.4 Flames  touching the cookpot shall be concealed and not able to come into contact  with hands or 
clothing.  
6.5 Flames or fuel shall  not protrude from any fuel loading area, storage container, or  flow-pipes during use.  
6.6 If the cookstove with a chimney fails a test in D.1.8 (a), a shield shall be employed to increase safety.  
The chimney shielding shall pass th e test in D.1.8 (b).  
6.7 For a stove with a chimney, the chimney shall exit outside the dwelling, and en sure the smooth flow of 
exhaust.  
6.8 For a stove with a chimney, there shall be no smoke leakage  
6.9 The stove with electrical fans shall have electri city safety controls.  DUS 761: 2017  
4 © UNBS 2017  – All rights reserved  
 7 Durability requirement s 
7.1 When subjected to the durability test, as specified in Annex E,  the stove shall maintain its basic structure 
and stability and shall not have broken parts,  cracks  and warping.   
7.2 The cookstove shall ha ve a lifespan of at least 2 years under  normal use  and a warranty  of 1 year  shall 
be given . 
8 Tests for cookstoves  
8.1 Manufacturer/supplier description  
The manufacturer/supplier shall provide documentation giving a detailed description  corresponding to th e 
stove provided. Information to be provided shall include:  
a) parts and assembly  instructions , where applicable,  
b) user instructions , 
c) dimensions,  
d) cooking power; and  
e) fuel type  
8.2 Visual  inspection  
Prior to the testing, a  detailed visual inspection of the coo kstove shall be conducted , noting the features in 
relation to the tests to be done . Observations  shall be recorded on a data sheet  as given in Annex F.  
Photographs  taken shall be attached to the data sheet . A ruler should be included in photographs, as a p oint 
of reference.  
8.3 Test procedures  
8.3.1  Cookstoves shall be subjected to the following tests in accordance with their respective annexes : 
a) thermal performance , Annex B  
b) emissions , Annex C  
c) safety , Annex  D 
d) durabilit y, Annex  E 
8.3.2  Results from the tests shall be reported in a test report given in Annex A.  
9. User instructions and safety precautions   
The cook stove shall be supplied with a suitable form of user instructions and safety precautions . DUS 761: 2017  
© UNBS 2017  – All rights reserved  5 
 10 Marking  and packaging  
10.1 Marking  
The stove shall be legibly and indelibly marked with  the following information  on the cookstove :  
a) Name of the manufacturer  and or trademark ; 
b) Country of origin;  
c) Classification;  
d) Serial/ Batch  number;  and 
e) reference  to this Uganda Standard . 
10.2 Packaging  
Stoves shall be packa ged in a suitable package  in order to protect them while in storage and transportation.  
The package shall contain the following information/d ocumentation ; 
a) name and address of manufacturer  
b) user instructions;  
c) safety  instructions;  
d) Parts list;  and 
d) Gross an d net weight . DUS 761: 2017  
6 © UNBS 2017  – All rights reserved  
 Annex A 
(normative)   
 
Test report  
The format of the stove performance test report is provided in Table A.1 . 
Table A.1  — Test report of cookstove  
Name and type of the stove:   Manufacturer:  
Fuel type and  water content:    Lower heating value, as received:   
Test site:   Test date:  
Standard referred:   Fan power (kW):   
Test environment conditions:   
Test equipment  and number of test 
repetitions   
Test items  Unit  Average  Standard deviation   
Thermal performance  Pc  kW      
ηc  %      
Emission factor  PM 2.5  mg/MJ      
CO  g/MJ      
Notes   
Test institution:   Tester:  
Examine and verify:   Sign and issue:  
 DUS 761: 2017  
© UNBS 2017  – All rights reserved  7 
 Annex B  
(normative)   
 
Thermal performance tests  
B.1 Thermal performance tes t  
B.1.1  Test equipment and instruments  
a) Weighing balance  with a resolution of 5 g and an accuracy of 1 .0 g;  
b) Stopwatch;  
c) Thermometers  with an accuracy of  1 C and resolution of 0.2 ℃;  
d) Humidity measuring device ;  
e) Wind speed measuring device  with a resolu tion of 0.5m/s.  
f) Moisture content measuring device, of accuracy to 1  
g) Fuel removing device  
h) Bomb calorimeter  
B.1.2  Pot size and water quantity  
The size of pot and water quantity used is determined according to the cooking power, as listed in Table B.1. 
Table B.1 — pot size and the water quantity  
Cooking power(kW)  Diameter of pot (mm)  Initial water(kg)  
≤2.0 240 5 
＞2.0 280 7 
 
B.2 Test conditions  
a) Ambient air temperature: 10 ℃ - 35℃; 
b) Relative humidity:<85%;  
c) Wind speed:<1.0  m/s; 
d) The test stove should be far away from other heat and combustion sources. If multiple stoves are to 
be tested in the same room,  the distance between each s tove should be greater than 3  m. 
B.3 Test preparation  
B.3.1 The tester shall be familiar with the operation of the stove and have sufficient experience  in testing 
stoves.  DUS 761: 2017  
8 © UNBS 2017  – All rights reserved  
 B.3.2 The instruments shall be calibrated.  
B.3.3 Use appr opriate fuel types according to the stove instructions.  
B.3.4 Weigh and record the mass, B of enough biomass fuels , based on a burning duration of 1 h. 
B.3.5 Measure the low calorific value of biomass fuel according to ISO 18125 . 
B.3.6 Weigh the water and then pour it into the pot. Record the initial mass of water , G1 and initial water 
temperature  T1.  
B.3.7 Place the thermometer in the pot using a holder; the sensor of the thermometer should be 5  cm above 
the bottom of the pot. Do not use a pot lid.  
B.4 Test steps  
B.4.1 Light the fire and record the time as t1  
B.4.2 When the water temperature has increased to the boiling point, record the temperature of the water T2 
and the time as  t2, and continue with the testing during the water evaporation phase.  
B.4.3 During the evaporation phase, record water temperature every 5 minutes.  
B.4.4 When the water temperature has dropped 5 ℃ below the boiling point, end the test, record the time t3, 
and weigh and record the water mass in the pot as G2. 
B.5 Calculation  
B.5.1 Useful energy  
Q1 = 4.18*G1 *(T2 −T1)+(G1 −G2)γ …1)  
Where ; 
Q1 the useful energy, kJ;  
G1 the initial mass of water in the pot, kg;  
G2 the final mass of water in the pot, kg;  
T1 the initial temperature of water, ℃; 
T2 the boiling point of the water, ℃; 
γ the latent  heat of water vaporization at boiling point, kJ/kg;  and 
4.18  the specific heat capacity of water, kJ/ (kg· ℃). 
B.5.2 Cooking power  
1 31
ttQPc
 ...2)  
Where ; 
Pc cooking power, kW;  DUS 761: 2017  
© UNBS 2017  – All rights reserved  9 
 (t3 −t1) test duration, s.  
B.5.3 Cooking thermal effici ency  
100
.1
arnetc
BQQ
 …3) 
Where ; 
ηc cooking thermal efficiency;  
B  mass of biomass fuel, kg;  
Qnet.ar  lower heating value (as received) of the biomass fuel, kJ/kg.  DUS 761: 2017  
10 © UNBS 2017  – All rights reserved  
 Annex C  
(normative)   
 
Emissions tests  
C.1 Emission measurements of PM 2.5 and CO  
C.1.1 Test preparation  
C.1.1.1  The test procedure shall depend on whether or not the stove has a chimney.  
C.1.1. 2 For a stove with a chimney, l ocate the hood over the stove chimney exhaust  (see Figure C.1) . 
Operate the blower at the flow rate that will be used during the test. Measure the static pressure imposed on 
the stove by the dilution tunnel (i.e., the difference in t he draft measured with and without the dilution tunnel 
operating) at a location no greater than 0.3m above the flue connector. Adjust th e distance between the top of 
the stove chimney and the hood so that the induced static pressure of the dilution tunnel is less than 1.25Pa. 
During this check and adjustment activity, no fire shall be in the stove.  
C.1.1.3 When the stove is burning at hig h burning rates, make sure that all emissions are captured by the 
hood system by adjusting the dilution tunnel flow rate or adjusting the distance between the top of the stove 
chimney and the hood, or both. The gas flow rate in the dilution tunnel should b e no less than 5m/s. If the 
distance between the top of the stove chimney and the hood decrease, recheck the static pressure imposed 
on the stove by the dilution tunnel according to C.1.1.2. 
C.1.1. 4 When testing stoves with low emissions, in order to ensur e sufficient capture of emissions in the 
form of mass collected on filters, additional dilution as shown in Figure C.1 should not be applied. When 
testing stoves with high emissions, additional dilution may be used to prevent overloading filters and to 
prevent instrument ranges from being exceeded. If increased air flow causes an excessive increase in hood 
face velocity, dilution air should be used to reduce hood face velocity. Dilution air may be filtered . 
C.1.1.5  For a stove without a chimney, locate the stove under the hood (see Figure C.2) . DUS 761: 2017  
© UNBS 2017  – All rights reserved  11 
 
 
Figure C.1 — Hood and dilution tunnel apparatus for collecting total emissions from cookstoves with 
chimneys  DUS 761: 2017  
12 © UNBS 2017  – All rights reserved  
 
 
Figure C.2 — Hood and dilution tunnel apparatus  
for collecting emissions from cookstoves without chimne ys 
C.1.2 Test method  
C.1.2.1  Locate the stove under the hood, and place the stove chimney just below the hood (See  Figure 
C.1).Flue gas emitted from the stove during the test is diluted and cooled by the ambient air, and then passes 
through the hood, the duct, the blower, and is discharged into the atmosphere. Measure the flow velocity in 
the duct according to the ISO 9096   
C.1.2.2 The sampling of PM 2.5 (See Fig ure C .3) shall be in accordance with  ISO 9096 , and the 
instruments and filter analysis procedure  shall be in accordance with ISO 25597 . The sampling and testing of 
CO procedure refer to the ISO 12039 . 
C.1.2.3 When ambient air is used as the dilution air, sample and analyse  ambient PM 2.5 and CO 
according to the ISO 25597 and ISO 4224 . DUS 761: 2017  
© UNBS 2017  – All rights reserved  13 
 
 
Figure.C.3 — Dilution sampling test for emission  
 
Figure C.4  — PM 2.5 sampling test  
C.1.3 Test steps  
C.1.3.1 Locate the stove below the hood, turn on the blower, measure the flow rate and adjust the valves 
to be sure that all emissions are captured and the flow rate is no less than 5  m/s.  
C.1.3.2 Start to sample both PM 2.5 and CO at the same time point as the fire is ignited. When the water 
temperature in the pot drops 5 ℃ below the boiling point, end the sampling and turn off the blower.  DUS 761: 2017  
14 © UNBS 2017  – All rights reserved  
 C.2 Calculation of Emission Fact ors  
C.2.1 PM 2.5  
EF PM2.5 =
0001
15.2QMPM  …4)  
M PM2.5 =
s
stM
VV  …5) 
M s =  
s
ssVVM
PM




5.2  …6)  
Where  
EFPM2.5 PM2.5 emission factor, mg/MJ;  
MPM2.5 the mass of PM2.5 emitted during the sampling period, mg;  
Vt volume of tot al exhaust in the dilution tunnel during the sampling period, m3;  
Vs volume of gas sampled during the sampling period, m3;  
Ms the mass of PM2.5 collected on the filter corrected for background, mg (if the dilution air passes 
through the High Efficiency P articulate Absorber ( HEPA ), and PM is removed efficiently, the 
correction is not necessary);  
M’s the mass of PM2.5 collected on the filter, mg;  
ρPM2.5 the concentration of PM2.5 in ambient air, mg/m3.  
C.2.2 CO 

1QVEFt CO CO
CO
   (7) 
 (7)  
Where:  
EFco  CO emission factor, g/MJ  
ρ’co the concentration of CO in the dilution tunnel, mg/m3  
ρco the concentration of CO in the ambient air, mg/m 3  
C.3 Testing repeats  
Repeat the test at least three times using the same method. Average the results for therm al efficiency and 
emission factors as the final reported value  DUS 761: 2017  
© UNBS 2017  – All rights reserved  15 
 Annex D  
(normative)   
 
safety tests and scoring tables  
D.1 Safety tests  
D.1.1 Sharp edges and points test  
D.1.1.1  Equipment  
Piece of cloth, rag, or loose clothing  
D.1.1.2  Procedure  
A piece of cotton cloth  shall be rubbed gently over the entire exterior surface of the cookstove to find areas 
that catch or tear the cloth . 
The safety rating for this hazard shall be determined by adding together the number of  times the cloth 
becomes caught or entangl ed. Th e sum shall then be applied to the metric in Table  D 1. 
Table D.1 — Scoring system for sharp edges and points test  
 
Number of catches  Rating  Score  
None  Best 4 
One or two  Good  3 
Three  Fair 2 
Four or more  Poor  1 
 
D.1.2 Cookstove tipping test  
D.1.2.1 Equipment:  
a) fuel; 
b) ruler / tape measure ; and  
c) calculator . 
D.1.2.2  Procedure  
a) Set stove on flat surface and load with fuel but do not ignite  
b) Pick a side to tip towards and measure the height of its tallest point  and record it as a standing height, 
H (see f igure D 1) DUS 761: 2017  
16 © UNBS 2017  – All rights reserved  
 Slowly tip cookstove in the outward direction from the side chosen until the stove begins to tip on its own  
Note  For the case of firewood stoves in which fuel is fed from the side  and protrudes outside , do not tip the 
stove from that side.  
c) Hold stove tilted where it can overturn an d measure new height, h (see figure D 1). 
 
Figure D.1a) — Measurement of H  
 
Figure D. 1b) — Measurement of h  
Figure D.1  — Showing how to measure stove standing height and tipped height  
d) Calcula te the ratio, R as per equation  
HhR
 …8) 
e) Repeat process as many times as there are legs on the stove (or four times for a circular base)  
f) Apply the result to table D.2 
Note  If the stove is fixed in position it automatically gets the bes t rating.  DUS 761: 2017  
© UNBS 2017  – All rights reserved  17 
 Table D.2 — Scoring system for cookstove tipping test  
 
Maximum ratio (R)  Rating  Score  
≤ 0.940  Best  4 
0.940 < R ≤ 0,961  Good  3 
0.961≤R <0.978  fair 2 
R≥0.978  poor  1 
 
D.1.3 Containment of fuel test  
This test provides a method for determining the likelihood for stoves to release  burning fuel whether standing 
upright or after being overturned . Enclosure of the combustion  chamber or fuel canister is important to restrict 
the uncontrolled movement of fuel during  use.  
D.1.3.1  Equipment  
a) fuel,  
b) ruler / tape measure,  
c) cookpot  
D.1.3.2  Procedure  
a) stock the cookstove with fuel but do not ignite  
b) place th e cook ing pot onto the cooking surface  
c) visually observe the gaps through which fuel can be seen;  
d) measure these gaps to determine their approximate areas.  
e) calculate the sum of these approximate areas  
f) use the summation of area, A, to find the rating  as per t able D 3 
Table D.3 — Scoring system for containment of fuel test  
Area exposed (A) (cm2) Rating  Score  
A ≤ 50  Best 4 
50 < A ≤ 150  Good  3 
150 < A ≤ 250  Fair 2 
A > 250  Poor  1 DUS 761: 2017  
18 © UNBS 2017  – All rights reserved  
 D.1.4 Obstructions near cooking surface test  
D.1.4.1  Equipment  
Ruler / tape mea sure 
D.1.4.2  procedure  
a) Inspect the cookstove for presence of the skirt; do not perform the test if skirt is present  
b) Measure height difference between the cooking surface and obstructions surrounding the cooking 
surface  
c) Use the largest height difference, D,  to find the rating  according to table D.4. 
Note  Stoves with skirts get good rating  
Table D.4 — Scoring system for obstructions near cooking surface test  
Maximum height difference (D)  
cm Rating  Score  
D ≤ 1  Best 4 
1 > D ≥ 2 .5 or cookstove with skirt  Good  3 
2.5 > D ≥ 4  Fair 2 
D > 4  Poor  1 
 
 
Figure 2  — schematic diagram of a stove with a skirt  DUS 761: 2017  
© UNBS 2017  – All rights reserved  19 
 D.1.5 Surface temperature test  
This test is employed with the intention that bur ns should not occur if the cookstove  surface is touched for a 
short duration . This short  duration is the time it takes for the body to react after touching something warm.  
D.1.5.1  Equipment  
a) fuel 
b) igniter  
c) chalk,  
d) ruler / tape measure,  
e) hand -held thermocouple  
f) cookpot  
D.1.5.2  Procedure  
a) Chalk 8 x 8 cm grid onto the cookstove. For horizontal marking the measurement shall start from the 
top of the cookstove.  
b) mark the grid intersections with a letter or number.  
c) Operate the cookstove at full output for 1 h before sta rting the measurement of temperature, with the 
cooking pot containing water placed over it  
d) Measure ambient air temp erature   
e) measure and record temperature  at grid intersections every after 10 minutes until a nearly constant 
surface temperature is attained . 
f) compute and record the temperature difference, T between air temperature and the highest recorded 
value of each intersection in ( e). 
g) use the maximum value of T in ( f) to find the rating as per table D 5 
Table D.5 — Scoring system for surface temperature test 
Difference between maximum temperature  
 and air temperature (T)  Rating  Score  
T ≤ 35  Best 4 
35 < T ≤ 45  Good  3 
45< T ≤ 50  Fair 2 
T > 50  Poor  1 
D.1.6 Heat transfer to the environment  test 
Large amounts of heat transmission to surroundings may ignit e combustibles or  construction in the area of the 
cookstove. Therefore cookstoves should not cause elevated  temperatures on surrounding surfaces in the 
environment  
D.1.6.1  Equipment 
a) fuel,  DUS 761: 2017  
20 © UNBS 2017  – All rights reserved  
 b) igniter,  
c) chalk,  
d) ruler / tape measure; and  
e) hand-held thermocouple  
D.1.6.2  Procedure: 
The following test procedures are used if the cookstove is placed within 10 cm of a  combustible or has a 
combustion chamber less than 5 cm in height from the ground. If th e stove is located outside these bounds it 
receives a rating of Be st.  
Note  For cookstoves that are  designed to be attached to the floor or wall, the procedures of this test should be 
omitted.  Instead the highest surface temperatures on the stove near where (5 cm from the wall or floor) it attaches to the 
ground or  wall are used for evaluation in this test.   
a) place the cookstove in its normal operating location and orientation  
b) sketch a n outline of the cookstove on the ground when looking  from above.  
c) sketch  an outline of the cookstove  on the wall while looking at the cooks tove from the  side, towards 
the wall.  
d) remove the cookstove and draw 8 x 8 cm approximate squares in a horizontal -vertical grid inside the 
outlines  on the floor and wall.  
e) return the cookstove to its normal operating location and orientation .  
f) measure ambien t air temperature  
g) operate the cookstove at full output for 1 h before starting the measurement of temperature, with the 
cooking pot containing water placed over it  
h) move the cookstove away to take temperature measurements for up to one minute at grid 
intersections on the floor and the wall,  
i) return the cookstove for at least five minutes.  
j) repeat steps (j) and (k) until all the grid intersections have been measured.  
k) compute the  temperatures difference, T, of the wall or floor with that of the ambient air  
l) use the maximum value of T in ( k) to find the rating as per table D 6 DUS 761: 2017  
© UNBS 2017  – All rights reserved  21 
 Table D.6 — Scoring system for heat transfer to the environment test  
 
Surface  Difference between maximum temperature  
 and air temperature (T)  Rating  Score  
Floor  T ≤ 45  Best  4 
45 < T ≤ 55  Good  3 
55 < T ≤ 65  Fair  2 
T ≤ 60  Poor   1 
Wall T > 80  Best 4 
60 < T ≤ 70  Good  3 
70 < T ≤ 80  Fair  2 
T > 65  Poor   1 
D.1.7 Handle temperature  test 
D.1.7.1  Equipment  
a) fuel,  
b) igniter,  
c) chalk,  
d) ruler / tape measure,  
e) hand-held thermocouple /infra -red  thermometer  
f) cookpot  of appropriate size  according to manufacturer’s instructions  
D.1.7.2  Procedure  
a) operate the cookstove at full output for 1 h before starting the measurement of temperature, with the 
cooking pot containing w ater placed over it  
b) measure ambient air temperature  
c) measure and record the temperature of all the parts of cookstove which may be necessary to touch 
during its operation every after 10 minutes until equilibrium is reached.  
Note  while measuring the tempera ture the thermometer shall be covered with a felt pad  or aluminium foil and kept 
in contact with that part for sufficient period of time until the maximum temperature is reached.  
d) compute and record the temperature difference, T between air temperature and the recorded value in 
(c). 
e) use the maximum value of T in (d ) to find the rating as per table D 7 
Table D.7 — Scoring system for handle temperature test  
 
Difference between maximum temperature  
and air temperature (T)  Rating  Score  
T ≤ 32  Best 4 
32 < T ≤ 38  Good  3 
38 < T ≤ 44  Fair 2 
T > 44  Poor  1 DUS 761: 2017  
22 © UNBS 2017  – All rights reserved  
 D.1.8 Chimney test  
Chimneys can become extremely hot during use and easily cause burns. The high  temperatures present on a 
chimney are from hot flue gases leaving the stove, often creati ng higher temperatures on the chimney than 
anywhere else on the stove.  
a) the ambient air and chimney surface  temperature are taken and applied against Table D.5 to  
determine a safety rating.  
b) if a shield is being used, measure the average area, A of the gaps . 
c) use the value obtained in (b) to find the rating as per table D 8 
Table D.8 — Scoring system for chimney shielding test  
Hole area (A) (cm2) Rating * Score  
A ≤ 10  Best 4 
10 < A ≤ 50  Good  3 
50 < A ≤ 150  Fair 2 
A > 150  Poor  1 
*Stoves without a chimney are scored best  
D.1.9 Flames surrounding cook ing vessel  test 
During this test the stove shall be  loaded with fuel and fully ablaze. The typical cookpot for t he stove shall be  
placed in its normal operating position to simulate how the stove is most often used. Amounts of uncovered 
flames surrounding the cookpot shall be  observed and applied to the metric given in Table D.9. 
Table D.9 — Scoring system for flame s surrounding cooking vessel test  
Amount of uncovered flames touching cooking vessel  Rating  Score  
None  Best 4 
Less than 4 cm up the sides of cooking vessel, not handles  Good  3 
Most of cooking vessel, not handles  Fair 2 
Entire cooking vessel and/or han dles Poor  1 
D.1.10  Flames exiting fuel chamber test  
a) with the cookstove fully ablaze  and a cooking pot on top , visually  inspect the amount, if any, of flames 
coming out of the fuel chamber, canister, or pipes and record if flames do or do not protrude  
b) rate the result in accordance with Table D.10 
Table D.10 — Scoring system for flames exiting fuel chamber test  
Occurrence of fire  Rating  Score  
Flames are 
contained  Best 4 
Flames protrude  Poor  1 DUS 761: 2017  
© UNBS 2017  – All rights reserved  23 
 D.1.11 Overall safety score  
To calculate the overall safety sc ore, the score fro m each of the 10 procedures is multiplied by a weighting 
factor based on Table D.11, and then summed for a total score:  
Table D.11 — Overall safety scoring system  
 
Procedure  Parameter*  Weight  
1 Sharp edges  1.5 
2 Tipping  3 
3 Containment  of fuel  2.5 
4 Obstructions near cooking surface  2 
5 Surface temperature  2 
6 Heat transfer to the environment  2.5 
7 Handle temperature  2 
8 Chimney  2.5 
9 Flames surrounding cooking vessel  3 
10 Flames exiting fuel chamber  4 
*For any stove to pass th e safety test, the minimum rating in each parameter 
shall be Good  
 
For procedures with multiple values, the minimum value is used to calculate the overall score. The total point 
score will be between 25 and 100.  DUS 761: 2017  
24 © UNBS 2017  – All rights reserved  
 Annex E  
(normative)   
 
Durability tests and scoring  
E.1 Durability tests  
Under normal circumstances durability test shall include inspection, extended run, impact test, corrosion, 
temperature resistance and quenching tests. However a simplified assessment may be based on an 
inspection after thermal and safety tests as well as a quenching test.  
E.1.1 Visual examination  after thermal performance and safety  tests 
Durability assessment of the cookstove shall be made by inspecting its state after thermal performance, 
emissions and safety tests. Thes e shal l be compared to it’s the s tate prior to testing.  If durability test is to be 
conducted, without the other tests, then the stove shall be inspected after it has been in operation at maximum 
power for six hours with a cooking pot on top.  
A detailed visual i nspection of the cookstove shall  be conducted, including documentation with photographs. 
Observations should be recorded on a data sheet. Whenever possible, a ruler should be included in 
photographs . Any signs of defects such as instability, discoloration,  cracks, twisted metal, broken 
components, warping etc . shall be noted.  
The scoring system for the quenching test is provided in, Table E.1.  
Table E.1 — Scoring system for inspection  
Level  Examples  Risk factor  Score  
No change  N/A +0 10 
Minor  Discolo uration, minor abrasion, 
etc. +1 8 
Major  Cracks < 2 cm in length, twisted 
metal, etc.  +3 4 
Critical  Broken components, cracks > 2 
cm in length, cloudy/hazy 
reflectors or glass, etc.  +5 0 
 
E.1.2 Quenching test  
E.1.2.1  Equipment  
Equipment required for this  test is as follows:  
a) representative fuel – enough for 5 h of operation;  
b) high temperature safety gloves and protective sleeves;  
c) safety glasses;  
d) cooking vessel with a diameter that is 20% less than the diameter of the cooking surface ; 
e) ruler;  and 
f) water contai ner or pitcher appropriate for pouring.  
E.1.2. 2 Procedure  
a) prior to testing, a detailed visual inspection of the cookstove should be conducted, including 
documentation with photographs. Observations should be recorded on a data sheet. Whenever 
possible, a ruler should be included in photographs, as a point of reference.  DUS 761: 2017  
© UNBS 2017  – All rights reserved  25 
 b) fill a cooking vessel with water to within 10 mm of the brim.  The cookstove should be run for 1 h. If 
cookstove power can be controlled, then the cookstove should be run at the maximum possi ble 
firepower.  
c) quickly pour an additional amount of water into the cooking vessel, causing overflow of water into the 
cookstove.  
d) allow at least 16 h for the cookstove to dry completely.  
e) repeat steps b) to d)  four times, for a total of five tests.  
f) post-testing observations and photographs should be taken and noted on the data sheet.  
NOTE  It is understood that some cookstove manufacturers specify the firepower for optimum performance. However, 
for this test the cookstove is operated at its maximum firepower, to model a worst -case scenario.  
WARNING  The tester should  wear safety glasses, high temperature safety gloves, and protective sleeves.  
WARNING  There  is a risk of water overflowing the container and/or hot cookstove components. Extreme caution should 
be tak en while conducting these tests.  
E.1.2.3  Scoring  
The scoring system for the quenching test is provided in  Table E.2 . 
Table E.2 — Scoring system for quenching test  
 
Level  Examples  Risk factor  Score  
No change  N/A +0 10 
Minor  Discolo uration or cracks  
< 2 c m in length  +1 8 
Major  Warped components or cracks  
> 2 cm in length  +3 4 
Critical  Broken or missing components,  
cloudy or hazy reflectors or glass, 
etc. +5 0 
NOTE  The score is obtained by multiplying by 2 and subtracting the risk factor 
from 10.  The f ormula used  is 10 –2 x (Risk factor )  
E.1.2.4 Overall durabili ty score  
To calculate the overall durability score, the score fro m each of the 2 procedures is multiplied by a weighting 
factor based on Table E.3, and then summed for a total sco re. 
Table E.3 — Overall durabili ty scoring system  
Procedure  Weight  
1 3 
2 7 DUS 761: 2017  
26 © UNBS 2017  – All rights reserved  
 Annex F  
(normative)   
 
Features for vi sual inspection  
Name and type of the stove:  Inspector:  
Product identity:  Inspection site:  
Manufacturer:  Date:  
Feature  Condition  Comment  
Cooking surface    
Liner    
Body (metal cladding)    
Handles    
Stands    
Pot rests    
Doors    
Air holes (if any)    
Combustion chamber    
Shelf    
Chimney    
Others    
NOTE  Condition shall either be G – Good, or B – Broken, or C – Cracked/Scratched  
 DUS 761: 2017  
© UNBS 2017  – All rights reserved  27 
 Bibliography  
[1] DKS 1814 -1:2017, Biomass stoves — Part 1: Performance requirements  
[2] GB/T 3402 1-2016 Clean biomass cookstove  
[3] IS.13152, Solid Bio -mass CHULHA -Specification, Part 1, Portable  
[4] Risk Analysis and Safety Evaluation of Household Stoves in Developing Nat ions by Nathan G Johnson   
 WDUS  761: 2017  
© UNBS 2017  – All rights reserved  29 
 Certification Marking  
Products that conform to Uganda standards may be marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The use of the UNBS Certification Mark is governed by th e Standards Act, and the Regulations made 
thereunder. This mark can be used only by those licensed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction with the relevant Uganda Standard. The 
presence of  this mark on a product or in relation to a product is an assurance that the goods comply with the 
requirements of that standard under a system of supervision, control and testing in accordance with the 
certification mark scheme of the Uganda National Bure au of Standards. UNBS marked products are 
continually checked by UNBS for conformity to that standard.  
Further particulars of the terms and conditions of licensing may be obtained from the Director, Uganda 
National Bureau of Standards.  
 WDUS 761: 2017    
 
ICS 97.040 20 
Price based on nn pages  
© UNBS 2017 – All rig hts reserved