2007 2009 2011 2013 2015

PSI Count PSI Rate PSI Severity Rate

PS Industry Wide Metric

Process Safety

Leading and Lagging Metrics

...You Don’t Improve What You Don’t Measure

CCPS

An AIChE Technology Alliance

Center for Chemical Process Safety

2013 2015

Revised: January 2011
2

CCPS

An AIChE Technology Alliance CCCenter for Chemical Process Safety

PS

An AIChE Technology Alliance

Center for Chemical Process Safety

An AIChE Industry Technology Alliance

Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure

Preface

The Center for Chemical Process Safety (CCPS®) was established in 1985 by the American Institute of Chemical 

Engineers (AIChE) for the express purpose of assisting industry in avoiding or mitigating catastrophic chemical 

accidents. More than 130 corporate members around the world drive the activities of CCPS.

In 2006, the CCPS Technical Steering Committee authorized the creation of a project committee to develop a 

Guideline book for the development and use of Leading and Lagging Process Safety Metrics. That committee 

identified that a key breakthrough opportunity for industry was the development of an industry lagging metric 

that would become the benchmark across the chemical and petroleum industry for measuring process safety 

performance. To achieve this objective, representatives and members from each of the major chemical and 

petroleum trade associations as well as other key global stakeholders were engaged. 

The outcome of that effort was published in December 2007. Many companies and organizations have used those 

metric definitions since 2008. Those definitions established in 2007 were a key input to the creation of a new 

ANSI/API standard (ANSI/API RP 754), which has been finalized and released in April 2010. CCPS and several 

members of the original CCPS Metric committee were involved in the API standard committee. 

CCPS has elected to update the original (December 2007) document describing the CCPS metric 

recommendations with minor revisions with the intent to align the CCPS and API documents. The intent is 

that if a company or organization utilizes either the CCPS or API definitions for the top tier process safety 

incident definitions that they will count the same incidents. However, there are a few principles described in 

the CCPS metric document which are not incorporated in the API document (e.g., the description and use of a 

severity-weighted metric). Since the API document references the CCPS definition it is important to retain both 

documents, yet maintain good alignment between the two.

There are also a few additions incorporated into the ANSI/API RP 754 document which may not be deemed 

necessary by all companies or trade associations internationally that have already began utilizing the 2007 CCPS 

document (e.g., the definitions of a “Tier 2” process safety event). This updated CCPS metric document will 

note those differences, yet describe those as “optional” metrics or definitions.

The ultimate goal of the 2006 CCPS project was to develop and then promote the use of common metrics across 

the industry and around the world. CCPS continues to support that objective, whether via adoption of the ANSI/

API RP 754 definitions or via use of this document.

1 American Petroleum Institute, ANSI/API Recommended Practice 754, Process Safety Performance Indicators for the Refining and 

Petrochemical Industries, First Edition, Washington D.C., 2010.
3

For more information on CCPS or these metrics 

please visit www.ccpsonline.org

CCPS Process Safety Metrics

“You don’t improve what you don’t measure”

Introduction...................................................................................................4

I. Lagging Metrics ........................................................................................................................ 6

 1.0 Process Safety Incident (PSI) (Tier 1 - PSE as per API-754): ....................................... 6

 Process Involvement ....................................................................................................... 6 

 Reporting Thresholds ...................................................................................................... 7

 Location .......................................................................................................................... 9

 Acute Release ................................................................................................................. 9

 Flowchart ........................................................................................................................ 9

 2.0 Tier 2 Process Safety Events (Tier 2 - PSE as per API 754) ....................................... 12 

 Tier 2 Indicator Purpose ............................................................................................... 12

 Process Involvement ..................................................................................................... 12

 Tier 2 Indicator Definition and Consequences ............................................................. 12

 3.0 Definitions ..................................................................................................................... 14

 4.0 Rate Adjusted Metrics .................................................................................................. 17

 5.0 Industry Process Safety Metrics ................................................................................... 17

 6.0 Applicability ................................................................................................................. 18

 7.0 Interpretations and Examples ....................................................................................... 19

II. Leading Metrics .................................................................................................................... 28

 1.0 Mechanical Integrity ..................................................................................................... 29

 2.0 Action Items Follow-up ................................................................................................ 30

 3.0 Management of Change ................................................................................................ 30

 4.0 Process Safety Training and Competency .................................................................... 33

 5.0 Safety Culture ............................................................................................................... 33

 6.0 Operating & Maintenance Procedures .......................................................................... 34

 7.0 Fatigue Risk Management ............................................................................................ 35

III. Near Miss Reporting and other Lagging Metrics ............................................................ 35

 Definition of a Process Safety Near Miss ............................................................................ 36

 Examples of Process Safety Near Miss ................................................................................ 36

 Maximizing Value of Near Miss Reporting .......................................................................... 38

Appendix A: UN Dangerous Goods Classification and Listing Chemicals ................................... 38

Appendix B: Additional Clarifications regarding UN Dangerous Goods lists & Exceptions ..........41
4

CCPS

An AIChE Technology Alliance CCCenter for Chemical Process Safety

PS

An AIChE Technology Alliance

Center for Chemical Process Safety

An AIChE Industry Technology Alliance

Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure

Introduction

An essential element of any improvement program is the measure of existing and future performance. Therefore, to 

continuously improve upon process safety performance, it is essential that companies in the chemical and petroleum 

industries implement effective leading and lagging process safety metrics. This document describes the recommendations assembled by the Center for Chemical Process Safety (CCPS) Process Safety Metric committee for a common 

set of company and industry leading and lagging metrics.

Within this document is a description of three types of metrics:

“Lagging” Metrics – a retrospective set of metrics that are based on incidents that meet the threshold of 

severity that should be reported as part of the industry-wide process safety metric.

“Leading” Metrics – a forward looking set of metrics which indicate the performance of the key work 

processes, operating discipline, or layers of protection that prevent incidents

“Near Miss” and other internal Lagging Metrics – the description of less severe incidents (i.e., below 

the threshold for inclusion in the industry lagging metric), or unsafe conditions which activated one or more 

layers of protection. Although these events are actual events (i.e., a “lagging” metric), they are generally 

considered to be a good indicator of conditions which could ultimately lead to a more severe incident.

These three types of metrics can be considered as measurements at different levels of the “safety pyramid” illustrated 

in Figure 1. Although Figure 1 is divided into four separate layers (Process safety incidents, Other incidents, Near 

miss, and Unsafe behaviors/Insufficient operating discipline), it is easier to describe metrics in terms of the categories 

shown above. Figure 1 illustrates how each of these four areas is captured under the three sections of this document.

It is strongly recommended that all companies incorporate each of these three types of metrics into their internal 

process safety management system. Recommended metrics for each of these categories are included in the three 

primary sections of this document.

Process Safety Incident: (Tier 1 PSEs as per API 754)

incidents which meet the threshold of severity which should be

reported as the industry-wide process safety metric.

Unsafe Behaviors or insufficient

operating discipline: 

measurements to ensure that safety protection layers

and operating discipline are being maintained.

Process Safety Event—Tier 2: (Tier 2 PSEs as per API 754)

incidents which didn't meet the definition of PS incident

for purposes of the industry PS incident metric.

(e.g., Loss of Primary Containment Incidents or fires causing Reportable incidents 

that restrict work, require medical treatment or were 10% of the TQ of a PSI)

Near Miss: Minor LOPCs or System failures

which could have led to an incident.

(e.g., instrument had failed, pipe wall thickness low)

}

}

Described in CCPS

Leading Metric section.

CCPS common 

Lagging indicators,

Described in this document

under the "Near Miss"

reporting section.

These two types of events

should be collected as 

independent or integrated 

"Near Miss" company metrics.

Collect for the learning

benefit, improve

awareness, and enhance

PS Culture.

Figure 1: Process Safety 

Metric Pyramid
5

For more information on CCPS or these metrics 

please visit www.ccpsonline.org

Tier 2 Process

Safety Events:

LOPCs with lesser significance

Near Miss:

Minor LOPCs, System failures which

could have led to an incident

Unsafe behaviors or insufficient

operating discipline

Process

Saftey

Incident H

A

Z

A

R

D

C

O

N

S

E

Q

U

E

N

C

E

H

A

Z

A

R

D

C

O

N

S

E

Q

U

E

N

C

E

H

A

Z

A

R

D

C

O

N

S

E

Q

U

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N

C

E

H

A

Z

A

R

D

C

O

N

S

E

Q

U

E

N

C

E

LEGEND:

Barriers or Layer of Protection

Mitigation & Emergency

Preparedness Measures

Failure of a barrier or 

mitigation measure

Figure 3: Process Safety Pyramid / Failed Protection Layers

Figure 2: Swiss Cheese Model 

Another way to consider metrics is that the incidents at the top of the pyramid reflect situations where failures to the 

multiple layers of protection which are intended to prevent an incident (both physical layers and work process/operating 

procedure layers) have failed, while the bottom of the pyramid reflects failures or challenges to one or two of these layers 

of protection – yet other layers continue to function. The multiple layer of protection concept is represented in Figure 2.

Incorporating the layer of protection concept, Figure 1 can then be redrawn as shown in Figure 3, to reflect that 

additional layers of protection or mitigation have failed as you progress from the bottom of the pyramid to the top.

• Hazards are contained by multiple 

protective barriers

• Barriers may have weaknesses or 

holes’

• When holes align, the hazard passes 

through the barriers resulting in the 

potential for adverse consequences.

• Barriers may be physical engineered 

containment or behavioral controls 

dependent on people

• Holes can be latent/incipient, or 

actively opened by people
6

CCPS

An AIChE Technology Alliance CCCenter for Chemical Process Safety

PS

An AIChE Technology Alliance

Center for Chemical Process Safety

An AIChE Industry Technology Alliance

Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure

I. Lagging Metrics

The BP US Refineries Independent Safety Review Panel (“Baker Panel”)2 and US Chemical Safety Board3 each 

recommended improved industry-wide process safety metrics in their final reports dealing with the 2005 explosion at 

the BP Texas City refinery. CCPS member companies also share the vision of a new industry-wide process safety metric, 

including a common set of definitions and threshold levels that will serve individual companies and industry as a whole by 

providing a mechanism to:

 • indicate changes in company or industry performance, to be used to drive continuous improvement 

 in performance; 

 • perform company-to-company or industry segment-to-segment benchmarking and 

 • serve as a leading indicator of potential process safety issues which could result in a catastrophic event.

This section of the document describes a set of definitions and metrics recommended as industry-wide lagging metrics.

1.0 Process Safety Incident (PSI) (Tier 1 PSE per API RP - 754):

For the purposes of the common industry-wide process safety lagging metrics, an incident is reported as a process safety

incident if it meets all four of the following criteria:

 (1) Process involvement

 (2) Above minimum reporting threshold

 (3) Location;

 (4) Acute release

Process Involvement

An incident satisfies the chemical or chemical process involvement criteria if the following is true:

A process must have been directly involved in the damage caused. For this purpose, the term 

"process" is used broadly to include the equipment and technology needed for chemical, petrochemical and refining production, including reactors, tanks, piping, boilers, cooling towers, 

refrigeration systems, etc. An incident with no direct chemical or process involvement, e.g., an 

office building fire, even if the office building is on a plant site, is not reportable.
7

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2 Baker, J.A. et al., “The Report of the BP U.S. Refineries Independent Safety Review Panel,” January 2007

http://www.bp.com/liveassets/bp_internet/globalbp/globalbp_uk_english/SP/STAGING/local_assets/assets/pdfs/Baker_panel_report.pdf

3 U.S. Chemical Safety and Hazard Investigation Board, Investigation Report No. 2005-04-I-TX, “Refinery Explosion and Fire,” BP, Texas 

City, March 2005.

An employee injury that occurs at a process location, but in which the process plays no direct part, is not reportable 

as a PSI (though it could be an OSHA or other agency reportable injury). The intent of this criterion is to identify 

those incidents that are related to process safety, as distinguished from personnel safety incidents that are not 

process-related. For example, a fall from a ladder resulting in a lost workday injury is not reportable simply because 

it occurred at a process unit. However, if the fall resulted from a chemical release, then the incident is reportable.

Reporting Thresholds

An unplanned or uncontrolled release of any material, including non-toxic and non-flammable materials (e.g., steam, hot 

condensate, nitrogen, compressed CO2 or compressed air), from a process that results in one or more of the consequences 

listed below:

Note: Steam, hot condensate, and compressed or liquefied air are only included in this definition if their release results in one of the 

consequences other than a threshold quantity release. However, other nontoxic, nonflammable gases with defined UNDG Division 2.2 

thresholds (such as nitrogen, argon, compressed CO2) are included in all consequences including, threshold releases

1. An employee or contractor day(s) away from work injury and/or fatality, or hospital admission and/or fatality of a third 

 party (non-employees/contractor)

2. An officially declared community evacuation or community shelter-in-place;

3. Fires or explosions resulting in greater than or equal to $25,000 of direct cost to the company, or;

4. An acute release of flammable, combustible, or toxic chemicals greater than the chemical release threshold quantities 

 described on Table 1. Note that table 1 has an additional threshold quantity level column which is recommended for 

 indoor releases 

 • Releases include pressure relief device (PRD) discharges, whether directly or via a downstream destructive device 

 that results in liquid carryover, discharge to a potentially unsafe location, on-site shelter-in-place, or public protective 

 measures (e.g., road closure)
8

CCPS

An AIChE Technology Alliance CCCenter for Chemical Process Safety

PS

An AIChE Technology Alliance

Center for Chemical Process Safety

An AIChE Industry Technology Alliance

Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure

For a full list of materials cross-referenced to the UN Dangerous Goods definitions, see chemical list or spreadsheet 

tools posted on the web site www.ccpsonline.org

Table 1 – Process Safety Incident Threshold Values

Threshold 

Release 

Category

Material Hazard 

Classifi cation a,c,d

Threshold 

Quantity

Recommended 

Threshold Quantity 

for indoorb releases 

(Optional )

1 TIH Zone A Materials 5 kg (11 lb) 2.5 kg (5.5 lb)

2 TIH Zone B Materials 25 kg (55 lb) 12.5 kg (27.5 lb)

3 TIH Zone C Materials 100 kg (220 lb) 50 kg (110 lb)

4 TIH Zone D Materials 200 kg (440 lb) 100 kg (220 lb)

5

Flammable Gases 

or Liquids with Initial Boiling Point ≤ 35 °C 

(95 °F) and Flash Point < 23 °C (73 °F) 

or Other Packing Group I Materials 

excluding strong acids/bases

500 kg (1100 lb) 250 kg (550 lb)

6

Liquids with Initial Boiling Point > 35 °C 

(95 °F) and Flash Point < 23 °C (73°F)

or Other Packing Group II Materials 

excluding moderate acids/bases

1000 kg (2200 lb 

or 

7 bbl

500 kg (1100 lb) 

or 

3.5 bbl

7

Liquids with Flash Point ≥ 23 °C (73 °F) 

and ≤ 60 °C (140 °F) or Liquids with Flash 

Point > 60 °C (140 °F) released at a temperature at or above Flash Point or strong acids/

bases or Other Packing Group III Materials

or Division 2.2 Nonflammable, Nontoxic 

Gases (excluding Steam, hot condensate, and 

compressed or liquefied air)

2000 kg (4400 lb) 

or 

14 bbl

1000 kg (2200 lb) 

or 

7 bbl

It is recognized that threshold quantities given in kg and lb or in lb and bbl are not exactly equivalent. 

Companies should select one of the pair and use it consistently for all recordkeeping activities.

a Many materials exhibit more than one hazard. Correct placement in Hazard Zone or Packing Group shall follow the rules of DOT 49 CFR 173.2a [14] 

 or UN Recommendations on the Transportation of Dangerous Goods, Section 2 [10]. See Annex B.

b A structure composed of four complete (floor to ceiling) walls, floor, and roof.

c For solutions not listed on the UNDG, the anhydrous component shall determine the TIH zone or Packing Group classification. The threshold quantity 

 of the solution shall be back calculated based on the threshold quantity of the dry component weight.

d For mixtures where the UNDG classification is unknown, the fraction of threshold quantity release for each component may be calculated. If the sum 

 of the fractions is equal to or greater than 100%, the mixture exceeds the threshold quantity. Where there are clear and independent toxic and 

 flammable conse quences associated with the mixture, the toxic and flammable hazards are calculated independently. See Annex A, Examples 29, 

 30 and 31.
9

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Location

An incident satisfies the location criteria if:

The incident occurs in production, distribution, storage, utilities or pilot plants of a facility reporting metrics 

under these definitions. This includes tank farms, ancillary support areas (e.g., boiler houses and waste water 

treatment plants), and distribution piping under control of the site. 

All reportable incidents occurring at a location will be reported by the company that is responsible for operating that 

location. This applies to incidents that may occur in contractor work areas as well as other incidents. 

At tolling operations and multi-party sites, the company that operates the unit where the incident initiated should 

record the incident and count it in their PSI metric.

For further clarification, look at the exclusions described in Section 6 (Applicability). 

Acute Release

A “1-hour” rule applies for the purpose of the reporting under this metric, i.e. the release of material reaches or 

exceeds the reporting threshold in any 1-hour period. If a release does not exceed the TQ level during any 1-hour 

period, it would not be treated as a PSI. Typically, acute releases occur in 1-hour or less; however, there may be 

some releases that would be difficult to prove if the threshold amount release occurred in 1-hour. (Example: A large 

inventory of flammable liquid is spilled from a tank or into a dike overnight due to a drain valve being left upon prior 

to a transfer operation. It may not be discovered for several hours, so it is difficult to know the exact time when the 

threshold quantity was exceeded.) If the duration of the release cannot be determined, the duration should be assumed 

to be 1 hour.

Flowchart

The criteria for reporting incidents as a PSI described above are illustrated in the attached flowchart (Figure 4). 

Figure 4: Determining if an incident meets definition of a reportable Process Safety Incident (PSI) under the 

definitions of the CCPS Industry Lagging Metric

Was Process Directly Involved 

in the Damage Caused?

Did the Incident Occur in Production, 

Distribution, Storage, Utilities, or Pilot 

Plants of a Facility reporting These Metrics?

Was there any unplanned or uncontrolled release 

of any material that resulted in....

An employee or contractor lost 

time injury or fatality, OR hospital 

admission or fatality of a third 

party (non-employee / contractor).

Fires or Explosions resulting 

in $25,000 of Direct Cost

to the Company?

An acute release of

flammable Combustible 

or toxic chemicals?

Was there an officially declared 

community evacuation or 

community shelter-in-place?

Reportable Process

Safety Incident

Does Not Meet Criteria for

Process Safety Incident

Yes 

Yes 

Yes 

Yes Yes Yes

No No

No

No 

No 

No
10

CCPS

An AIChE Technology Alliance CCCenter for Chemical Process Safety

PS

An AIChE Technology Alliance

Center for Chemical Process Safety

An AIChE Industry Technology Alliance

Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure

Severity Level

(Note 4)

 NA

4

(1 point used in severity 

rate calculations for each 

of the attributes which 

apply to the incident)

3

(3 points used in severity 

rate calculations for each 

of the attributes which 

apply to the incident)

2

(9 points used in severity 

rate calculations for each 

of the attributes which 

apply to the incident)

1

(27 points used in severity

rate calculations for each 

of the attributes which 

apply to the incident)

Safety/Human Health

(Note 5)

Does not meet or 

exceed Level 4 threshold

Injury requiring treatment beyond first aid to 

employee or contractors 

(or equivalent, Note 1) 

associated with a process 

safety incident

(In USA, incidents meeting the definitions of an 

OSHA recordable injury)

Lost time injury to 

employee or contractors 

associated with a process 

safety event

On-site fatality - employee 

or contractors associated with a process safety 

event; multiple lost time 

injuries or one or more 

serious offsite injuries 

associated with a process 

safety event.

Off-site fatality or multiple on-site fatalities 

associated with a process 

safety event.

Fire or Explosion 

(including overpressure)

Does not meet or exceed 

Level 4 threshold

Resulting in $25,000 to 

$100,000 of direct cost

Resulting in $100,000 to 

1MM of direct cost.

Resulting in $1MM to 

$10MM of direct cost.

Resulting in direct cost 

>$10MM

Potential Chemical 

Impact

(Note 3)

Does not meet or exceed 

Level 4 threshold

Chemical released within 

secondary containment or 

contained within the unit - 

see Note 2A

Chemical release outside of containment but 

retained on company 

property 

OR 

flammable release without 

potential for vapor cloud 

explosives - see Note 2B

Chemical release with 

potential for injury off 

site or flammable release 

resulting in a vapor cloud 

entering a building or 

potential explosion site 

(congested/confined area) 

with potential for damage 

or casualties if ignited - 

see Note 2C

Chemical release with 

potential for significant 

on-site or off-site injuries 

or fatalities - see Note 2D

Community/Environment 

Impact

(Note 5)

Does not meet or exceed Level 

4 threshold

Short-term remediation to address 

acute environmental impact. 

No long term cost or company 

oversight. 

Examples would include spill 

cleanup, soil and vegetation 

removal. 

Minor off-site impact with precautionary shelter-in-place

OR

Environmental remediation 

required with cost less than 

$1MM. No other regulatory oversight required.

OR 

Local media coverage

Shelter-in-place or community 

evacuation 

OR

Environmental remediation 

required and cost in between 

$1MM - $2.5 MM. State government investigation and oversight 

of process. 

OR 

Regional media coverage or brief 

national media coverage.

National media coverage over 

multiple days 

OR 

Environmental remediation 

required and cost in excess of $2.5 

MM. Federal government investigation and oversight of process. 

OR 

other significant community 

impact

A severity level will be assigned for each consequence category for each process safety incident utilizing the criteria shown in 

Table 2.

Table 2: Process Safety Incidents & Severity Categories

Process Safety Incident Severity
11

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NOTE 1: For personnel located or working in process manufacturing facilities.

NOTE 2: It is the intent that the “Potential Chemical Impact” definitions shown in Table 2 to provide sufficient definition such that plant owners or users of this metric can select from the appropriate qualitative severity descriptors 

without a need for dispersion modeling or calculations. The user should use the same type of observation and judgment typically used to determine the appropriate emergency response actions to take when a chemical release occurs. 

However, CCPS does not want to preclude the use of a “sharper pencil” (e.g. dispersion modeling) if a company so 

chooses. In those cases, the following notes are being provided, as examples, to clarify the type of hazard intended 

with the four qualitative categories:

A: AEGL-2/ERPG-2 concentrations (as available) or 50% of Lower Flammability Limits (LFL) does not extend 

beyond process boundary (operating unit) at grade or platform levels, or small flammable release not entering a potential explosion site (congested/confined area) due to the limited amount of material released or location of release (e.g., 

flare stack discharge where pilot failed to ignite discharged vapors). 

B: AEGL-2/ERPG-2 concentrations (as available) extend beyond unit boundary but do not extend beyond property 

boundary. Flammable vapors greater than 50% of LFL at grade may extend beyond unit boundaries but did not entering a potential explosion site (congested/confined area); therefore, very little chance of resulting in a VCE.

C: AEGL-2/ERPG-2 concentrations (as available) exceeded off-site OR flammable release resulting in a vapor cloud 

entering a building or potential explosion site (congested/confined area) with potential for VCE resulting in fewer than 

5 casualties (i.e., people or occupied buildings within the immediate vicinity) if ignited.

D: AEGL-3/ERPG-3 concentrations (as available) exceeded off-site over the defined 10/30/60 minute time frame OR 

flammable release resulting in a vapor cloud entering a building or potential explosion site (congested/confined area) 

with potential for VCE resulting in greater than 5 casualties (i.e., people or occupied buildings within the immediate 

vicinity) if ignited.

NOTE 3: The Potential Chemical Impact table reflects the recommended criteria. However, some companies may 

object to making a relative ranking estimate on the potential impact using the terms described. In those situations, 

it would be acceptable for those companies to substitute the following criteria corporate wide: Severity Level 4: 

1X to 3X the TQ for that chemical, Level 3: 3X to 9X, Level 2: 9X to 20X, and Level 1: 20X or greater the TQ for 

that chemical. However, if a company elects to use this alternative approach they should be consistent and use this 

approach for all releases. They should not select between the two methods on a case-by-case basis simply to get the 

lowest severity score.

NOTE 4: The category labels can be modified by individual companies or industry associations to align with the 

severity order of other metrics. It is important is to use the same severity point assignments shown.

NOTE 5: The severity index calculations include a category for “Community/Environmental” impact and a first aid 

(i.e., OSHA “recordable injury”) level of Safety/Human Health impact which are not included in the PSI threshold 

criteria. However, the purpose of including both of these values is to achieve greater differentiation of severity points 

for incidents that result in any form or injury, community, or environmental impacts.
12

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PS

An AIChE Technology Alliance

Center for Chemical Process Safety

An AIChE Industry Technology Alliance

Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure

Tier 2 Indicator Purpose

The count of Tier 2 Process Safety Events represent those LOPC incidents with a lesser consequence than a PSI. 

Tier 2 PSEs, even those that have been contained by secondary systems, indicate barrier system weaknesses that may 

be potential precursors of future, more significant incidents. In that sense, Tier 2 PSEs can provide a company with 

opportunities for learning and improvement of its process safety performance. 

Process Involvement

The same Process Involvement criteria apply to Tier 2 – PSEs as apply to PSI (Tier 1 – PSEs)

Tier 2 Indicator Defi nition and Consequences

A Tier 2 PSE is an event with lesser consequence then a PSI event. A Tier 2 LOPC is an unplanned or uncontrolled 

release of any material, including non-toxic and non-flammable materials (e.g. steam, hot condensate, nitrogen, compressed CO2 or compressed air), from a process that results in one or more of the consequences listed below and is not 

reported in Tier 1:

NOTE Steam, hot condensate, and compressed or liquefied air are only included in this definition if their release

 results in one of the consequences other than a threshold quantity release. However, other nontoxic, 

 nonflammable gases with defined UNDG Division 2.2 thresholds (such as nitrogen, argon, compressed CO2)

 are included in all consequences including, threshold releases

 1. an employee, contractor or subcontractor recordable injury;

 2. a fire or explosion resulting in greater than or equal to $2,500 of direct cost to the Company;

 3. An acute release of flammable, combustible, or toxic chemicals from the primary containment 

 (i.e., vessel or pipe) greater than the release threshold quantities described on Table 2, Note that 

 table 2 has an threshold quantity level column which are recommended for indoor releases.

 o including pressure relief device (PRD) discharges, whether directly or via a 

 downstream destructive device that results in liquid carryover, discharge to a 

 potentially unsafe location, on-site shelter-in-place, or public protective measures 

 (e.g., road closure)

2.0 Tier 2 Process Safety Events (Tier 2 - PSE as per API 754)
13

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Threshold 

Release 

Category

Material Hazard 

Classifi cation a,c,d

Threshold 

Quantity

Recommended 

Threshold Quantity 

for indoorb releases 

(Optional )

1 TIH Zone A Materials 0.5 kg (1.1 lb) 0.25 kg (0.55 lb)

2 TIH Zone B Materials 2.5 kg (5.5 lb) 1.2 kg (2.8 lb)

3 TIH Zone C Materials 10 kg (22 lb) 5 kg (11 lb)

4 TIH Zone D Materials 20 kg (44 lb) 10 kg (22 lb)

5

Flammable Gases or

Liquids with Initial Boiling Point ≤ 35 °C (95 

°F) and Flash Point < 23 °C (73 °F)

or Other Packing Group I Materials 

excluding strong acids/bases

50 kg (110 lb) 25 kg (55 lb)

6

Liquids with a Initial Boiling Point > 35 °C 

(95 °F) and Flash Point < 60 °C (140 °F)

or Liquids with Flash Point > 60 °C (140 °F) 

released at or above Flash Point;

Or Other Packing Group II and III Materials 

excluding moderate acids/bases

or Strong acids and bases 

100 kg (220 lb)

or

1 bbl

50 kg (110 lb)

or

0.5 bbl

7

Liquids with Flash Point > 60 °C (140 °F) 

released at a temperature below Flash Point

or Moderate acids/bases or Division 2.2 

Nonflammable, Nontoxic Gases

(excluding Steam, hot condensate, and 

compressed or liquefied air)

1000 kg (2200 lb)

or

10 bbl

500 kg (1100 lb)

or

5 bbl

In order to simplify determination of reporting thresholds for Tier 2, Categories 6 and 7 in Tier 1 have been combined into one 

category in Tier 2 (Category 6). A new category 7 has been added.

a Many materials exhibit more than one hazard. Correct placement in Hazard Zone or Packing Group shall follow the rules of DOT 49 CFR 173.2a [14] 

 or UN Recommendations on the Transportation of Dangerous Goods, Section 2 [10]. See Annex B.

b A structure composed of four complete (floor to ceiling) walls, floor and roof.

c For solutions not listed on the UNDG, the anhydrous component shall determine the TIH zone or Packing Group classification. The threshold quantity 

 of the solution shall be back calculated based on the threshold quantity of the dry component weight.

d For mixtures where the UNDG classification is unknown, the fraction of threshold quantity release for each component may be calculated. If the sum 

 of the fractions is equal to or greater than 100%, the mixture exceeds the threshold quantity. Where there are clear and independent toxic and 

 flammable consequences associated with the mixture, the toxic and flammable hazards are calculated independently. See Annex A, Examples 

 29, 30 and 31.

Location and Acute Release Criteria

The same location and acute release criteria apply to Teir 2 – PSEs as apply to PSIa (Tier 1 – PSEs)

Table 3 – Process Safety Incident Threshold Values
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Acids/Bases, Moderate 

Substances with pH ≥ 1 and < 2, or pH > 11.5 and ≤ 12.5, or more precisely, substances that cause full thickness destruction of intact skin tissue within an observation period up to 14 days starting after the exposure time of 60 minutes or less, 

but greater than three minutes, consistent with Globally Harmonized System of Classification and Labeling of Chemicals 

(GHS) Skin Corrosion Category 1B. 

Acids/Bases, Strong 

Substances with pH < 1 or > 12.5, or more precisely, substances that cause full thickness destruction of intact skin tissue 

within an observation period up to 60 minutes starting after the exposure time of three minutes or less, consistent with 

GHS Skin Corrosion Category 1A. 

Acute Release: A sudden release of material that reaches or exceeds the reporting threshold in any one (1) hour period.

BBL: Barrels; 42 U.S. gallons (35 Imperial gallons)

Company: "Company" (when designated with a capital C) or "the Company", refers to the operating company in the refining and petrochemical industries and/or any of its divisions, and/or any of its consolidated affiliates.

Contractor: Any individual not on the Company payroll, including subcontractors, whose exposure hours, injuries and illnesses are routinely tracked by the host Company.

Days Away From Work Injury

Work-related injuries that result in the employee being away from work for at least one calendar day after the day of the 

injury as determined by a physician or other licensed health professional. This is an abridged version of the definition used 

to report days away from work injuries for OSHA. 

Deflagration Vent

An opening in a vessel or duct that prevents failure of the vessel or duct due to overpressure. The opening is covered by a 

pressure-relieving cover (e.g. rupture disk, explosion disk, or hatch).

Destructive Device

A flare, scrubber, incinerator, quench drum, or other similar device used to mitigate the potential consequences of a PRD 

release.

Direct Cost: Cost of repairs or replacement, cleanup, material disposal, environmental remediation and emergency 

response. Direct cost does not include indirect costs, such as business opportunity, business interruption and feedstock/

product losses, loss of profits due to equipment outages, costs of obtaining or operating temporary facilities, or costs of 

obtaining replacement products to meet customer demand. Direct cost does not include the cost of the failed component 

leading to LOPC, if the component is not further damaged by the fire or explosion.

Employee: Any individual on the Company payroll and whose exposure hours, injuries and illnesses are routinely tracked 

by the Company. Individuals not on the Company payroll, but providing services under direct company supervision are also 

included (e.g. government sponsored interns, secondees, etc.). 

Explosion: A release of energy that causes a pressure discontinuity or blast wave (e.g. detonations, deflagrations, and 

rapid releases of high pressure caused by rupture of equipment or piping).

3.0 Definitions
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Facility

The buildings, containers or equipment that contain a process.

Fire

Any combustion resulting from a LOPC, regardless of the presence of flame. This includes smoldering, charring, smoking, 

singeing, scorching, carbonizing, or the evidence that any of these have occurred.

Flammable Gas

Any material that is a gas at 35 °C (95 °F) or less and 101.3 kPa (14.7 psi) of pressure and is ignitable when in a mixture 

of 13 % or less by volume with air, or has a flammable range of at least 12% as measured at 101.3 kPa (14.7 psi).

Hospital Admission

Formal acceptance by a hospital or other inpatient health care facility of a patient who is to be provided with room, board, 

and medical service in an area of the hospital or facility where patients generally reside at least overnight. Treatment in the 

hospital emergency room or an overnight stay in the emergency room would not by itself qualify as a “hospital admission.”

Loss Of Primary Containment (LOPC): An unplanned or uncontrolled release of material from primary containment. 

including non-toxic and non-flammable materials (e.g. steam, hot condensate, nitrogen, compressed CO2 or compressed air).

Major Construction

Large scale investments with specific, one-time project organizations created for design, engineering, and construction of 

new or significant expansion to existing process facilities.

Material

Substance with the potential to cause harm due to its chemical (e.g. flammable, toxic, corrosive, reactive, asphyxiate) or 

physical (e.g. thermal, pressure) properties.

Office Building

Buildings intended to house office workers (e.g. administrative or engineering building, affiliate office complex, etc.).

Officially Declared

A declaration by a recognized community official (e.g. fire, police, civil defense, emergency management) or delegate (e.g. 

Company official) authorized to order the community action (e.g. shelter-in-place, evacuation).

Pressure Relief Device (PRD)

A device designed to open and relieve excess pressure (e.g. safety valve, thermal relief, rupture disk, rupture pin, 

deflagration vent, pressure/vacuum vents, etc.).

Primary Containment: A tank, vessel, pipe, rail car or equipment intended to serve as the primary container or used 

for the transfer of the material. Primary containers may be designed with secondary containment systems to contain and 

control the release. Secondary containment systems include, but are not limited to, tank dikes, curbing around process 

equipment, drainage collection systems into segregated oily drain systems, the outer wall of double walled tanks, etc.

Definitions con't.
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Process

Production, distribution, storage, utilities, or pilot plant facilities used in the manufacture of chemical, petrochemical and petroleum refining products. This includes process equipment (e.g. reactors, vessels, piping, furnaces, boilers, pumps, compressors, 

exchangers, cooling towers, refrigeration systems, etc.), storage tanks, ancillary support areas (e.g. boiler houses and waste 

water treatment plants), on-site remediation facilities, and distribution piping under control of the Company.

Process Safety

A disciplined framework for managing the integrity of hazardous operating systems and processes by applying good design 

principles, engineering, and operating and maintenance practices.

Process Safety Event (PSE)

An unplanned or uncontrolled LOPC of any material including non-toxic and non-flammable materials (e.g. steam, hot condensate, nitrogen, compressed CO2 or compressed air) from a process, or an undesired event or condition that, under slightly 

different circumstances, could have resulted in a LOPC of a material.

PSI: Process Safety Incident. 

Secondary Containment

System designed to contain or control a release from primary containment. Secondary containment systems include, but are 

not limited to tank dikes, curbing around process equipment, drainage collection systems, the outer wall of double walled 

tanks, etc.

Public Receptors

Offsite residences, institutions (e.g. schools, hospitals), industrial, commercial, and office buildings, parks or recreational areas 

where members of the public could potentially be exposed to toxic concentrations, radiant heat, or overpressure, as a result of a 

LOPC.

Recordable Injury

A work-related injury that results in any of the following: death, days away from work, restricted work or transfer to another 

job, medical treatment beyond first aid, loss of consciousness, or a significant injury diagnosed by a physician or other licensed 

health professional. This is an abridged version of the definition used to report days away from work injuries for OSHA. 

Third Party: Any individual other than an employee, contractor or subcontractor of the Company. [e.g., visitors, non-contracted delivery drivers (e.g. UPS, U.S. Mail, Federal Express), residents, etc.].

Tolling Operation

A company with specialized equipment that processes raw materials or semi-finished goods for another company.

Total employee, contractor & subcontractor work hours: Total hours worked for refining, petrochemical, or chemical 

manufacturing facilities. Using the same definitions that would be applicable for the OSHA injury/illness formula. Man-hours 

associated with major construction projects or corporate administration would not be included.

United Nations Dangerous Goods (UNDG) hazard categories: A classification system used to evaluate the potential hazards of various chemicals, if released, used by most international countries as part of the product labeling or shipping information. In the United States, these hazard categories are defined in US Department of Transportation regulations (49 CFR 

172.101). and listed in 49 CFR 172, Subpart B For more information on this ratings, see the UN web site 

(http://www.unece.org/trans/danger/publi/adr/adr2007/07ContentsE.html)

Definitions con't.
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Utilizing the definitions described above, there are a variety of rate-based metrics which can be generated. These 

include:

Process Safety Total Incident Rate (PSTIR): Total PS incidents x 200,000

 Total employee & contractor work hours

Process Safety Incident Severity Rate (PSISR) (i.e., severity-weighted Process Safety incident rate formula):

 PSISR = Total severity score for all PS incidents x 200,000

 Total employee, contractor & subcontractor work hours

In determining this rate, 1 point is assigned for each Level 4 incident attribute, 3 points for each Level 3 attribute, 9 

points for each Level 2 attributes, and 27 points for each Level 1 attributes. Theoretically, a PSI could be assigned a 

minimum of 1 point (i.e., the incident meets the attributes of a Level 4 incident in only one category) or a maximum of 

108 points (i.e., the incident meets the attributes of a Level 1 incident in each of the four categories..

PS Level “X*” incident rate: Total Severity Level “X*” PS incidents x 200,000

 Total employee, contractor & subcontractor work hours

Where X* can be the total count of Severity Level 4, 3, 2, or 1 incidents. The severity level of an incident is the maximum severity rating of the four consequence categories.

 

 Tier 2 PSE Rate (Tier 2 IR): Total Tier 2 PSE Count x 200,000

 Total employee & contractor work hours

It is recommended that companies implement and publicly report the following three process safety metrics.

Total Count of Process Safety Incidents (PSIC): The count of all incidents which meet the definitions of a PSI 

described within this document.

Process Safety Total Incident Rate (PSTIR): The cumulative (annual) count of incidents normalized by man-hours, 

per the formula described in section 2.0.

Process Safety Incident Severity Rate (PSISR): The cumulative (annual) severity-weighted rate of process safety 

incidents per the formula described in section 2.0.

To assist in benchmarking, it would be beneficial if trade associations or consortiums collect and publish this information for member companies.

Optionally, companies should also consider implementing and publicly reporting the count and rate of Tier 2 Process 

Safety Events.

4.0 Rate Adjusted Metrics

5.0 Industry Process Safety Metrics
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It is recommended that companies record and report PSIs occurring at Company-owned or operated facilities, except

as noted below:

1. PSIs that originated off Company property;

2. Marine transport vessel incidents, except when the vessel is connected to the facility for the purposes of feedstock or product transfer;

3. Truck and/or rail incidents, except when the truck or rail car is connected to the facility for the purposes of 

feedstock or product transfer;

4. Vacuum truck operations, except on-site truck loading or discharging operations, or use of the vacuum truck 

transfer pump;

5. Routine emissions that are allowable under permit or regulation;

6. Office, shop, and warehouse building incidents (e.g., office heating equipment explosions, fires, spills, releases, 

personnel injury or illness, etc.);

7. Personnel safety "slip/trip/fall" incidents that are not directly associated with evacuating from, or responding to 

a loss of containment incident;

8. Loss of Primary Containment (LOPC) incidents from ancillary equipment not connected to the process (e.g., 

small sample containers);

9. Planned and controlled drainage of material to collection or drain system designed for such service (Note: 

Exclusion does not apply to an unintended and uncontrolled release of material from primary containment that 

flows to a collection or drain system);

10. Mechanical work being conducted outside of process units or in maintenance shops; and,

11. Quality Assurance (QA), Quality Control (QC) and Research and Development (R&D) laboratories are excluded. (Pilot plants are included.)

12. On-site fueling operations of mobile and stationary equipment (e.g. pick-up trucks, diesel generators, and heavy 

equipment).

6.0 Applicability
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The following interpretations and examples have been prepared to help clarify areas of potential uncertainty in the evaluation of reportable Process Safety Incidents (PSI).

They are for illustrative purposes only. The following areas are addressed:

➢ Company Premises

➢ PSIs With Multiple Outcomes

➢ Loss Of Containment

➢ Acute Releases

➢ Flares & Emission Control Devices

➢ Safety Relief Device/System

➢ Toxic Gas, Vapor or Aerosol

➢ Lost Time Incidents

➢ Pipelines

➢ Fires Not Associated with Chemical Release 

➢ Marine Vessels

➢ Truck and Rail

➢ Office Building

➢ Man-Machine Interface Incidents

➢ Examples of Use of Assignment of Severity Scores

➢ Mixtures

➢ Vacuum Truck Operations

➢ Direct Costs

➢ Officially Declared Evacuation or Shelter-in -Place

COMPANY PREMISES

1. A third-party truck loading a flammable product on Company Premises, experiences a leak and subsequent fire 

and property loss damages of $75,000 (direct costs). Although the truck is "Operated-by-Others", it is connected to 

the process. The incident would be a reportable PSI if property losses in direct costs were equal to or greater than 

$25K or some other PSI threshold was met or exceeded (e.g., a fatality).

2. Similar example as #1. The truck loaded with flammable product overturns in route out of the plant, resulting in a 

fire and loss of the truck. This would not be reported as a PSI since the truck is no longer connected to the plant. 

3. A pipeline leaks and releases 2000 lb of flammable vapor above ground within 1 hour. A public road bisects the 

main facility and its marine docks. This pipeline originates in the facility and goes to the docks. The leak site happens to be off the site’s property in the short segment of piping that runs over the public road. Although the leak 

technically occurs off-site, this is a reportable PSI since the facility owns and operates the entire segment of pipeline.

7.0 Interpretations and Examples
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PSIs WITH MULTIPLE OUTCOMES

4. There is a 200 bbl spill of flammable liquid that results in significant flammable vapor being released, ignited 

and causing a fire. The fire damages other equipment resulting in a toxic gas release above the reporting threshold, along with multiple lost time injuries, including a fatality. This event should be reported as a single PSI, but 

with multiple outcomes. When applying the severity metric, the appropriate severity point assignment (1, 3, 9, 

or 27 points each) would be selected from Table 2 for the fire damage, the chemical release potential impact, the 

human health impact, and the community/environmental impact. The sum of these individual severity points 

will be used in calculating the overall severity rate metric. 

LOSS OF CONTAINMENT

5. Ten barrels of gasoline (1400 kg, 3100 lbs.) leak from piping onto concrete and the gasoline doesn't reach soil 

or water. Site personnel estimate that the leak was "acute" (e.g., occurred within a 1-hour timeframe). This is a 

reportable PSI because there was an "acute” loss of primary containment (e.g., within "1 hour") of 1000 kg (2200 

lbs) or more of ”Flammable Liquid”.

6. A faulty tank gauge results in the overfilling of a product tank containing “flammable liquids”. Approximately 

7000 kg (15500 lbs) of liquid overflows into the tank's diked area. This incident is a reportable PSI since it is an 

"acute" spill greater than 2200 lbs, regardless of secondary containment.

7. A maintenance contractor opens a process valve and gets sprayed with sulfuric acid resulting in a severe burn and 

lost time injury. This would be a reportable PSI. It is an unintended event involving a material and a loss of containment. For fatalities and days away from work injuries and illnesses, there is no release threshold amount.

8. An operator opens a quality control sample point to collect a routine sample of product and receives a bad hand 

laceration requiring stitches due to a broken glass bottle and misses the next day of work. This is not a reportable 

PSI because it is not related to a loss of containment.

9. A bleeder valve is left open after a plant turnaround. On startup, an estimated 10 bbls of fuel oil (1700 kg, 

3750 lbs.) is released, at 100°F, onto the ground and into the plant’s drainage system before the bleeder is 

found and closed. This would not be a PSI because it is less then the release criteria of 2000 kg or 4400 lbs of a 

”Combustible Liquid”. 

10. Operations is draining water off of a crude oil tank (operated at 120°F) into a drainage system designed for that 

purpose. The operator leaves the site and forgets to close the valve. 20 bbls of crude oil is released into the drainage system. This would be a PSI because the release of crude oil, a “Combustible Liquid”, is unintended and it is 

greater then the release criteria of 2000 kg or 4400 lbs. 

11. A pipe corrodes and leaks 10 Bbls (1700 kg, 3750 lbs.) of Heavy Cycle Oil (HCO) at the operations temperature 

of 550°F to the ground. The HCO has a flash point of 300°F.. This would not be a PSI. Although the HCO is 

a high flash material released above its flash point, the release did not exceed the threshold quantity of 2000 kg 

(4400 lbs) or 14 bbls. 

12. An operator purposely drains 20 bbls of combustible material into an oily water collection system within one 

hour as part of a vessel cleaning operation. The drainage is planned and controlled and the collection system is 

designed for such service. This is not a reportable PSI since it is consistent with a specific exclusion. If the 
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material had been unintentionally released or it had become uncontrolled and flowed to an open drain, sewer or 

other collection system, it would be a reportable PSI.

13. Hydrocarbon fumes migrate into the QA/QC laboratory located within the facility and results in a fire with $5000 

damage. The source of the hydrocarbon fumes is the oily water sewer system. Although the fire was the result of 

an unplanned or uncontrolled loss of primary containment, this incident is not a PSI since the damage threshold 

of $25,000 was not exceeded.

14. A forklift truck delivering materials inside a process unit knocks off a bleeder valve leading to the release of isopentane and a subsequent vapor cloud explosion with asset damage greater than $25,000. This is a PSI since an 

unplanned or uncontrolled LOPC resulted in a fire or explosion causing greater than $25,000 damage.

15. There is a loss of burner flame in a fired heater resulting in a fuel rich environment and subsequent explosion 

in the fire box with greater than $25,000 in damages to the internals of the heater. There was no release outside 

of the fire box. This would be a reportable PSI since after the flameout the continuing flow of fuel gas is now 

an uncontrolled release. The intent is for combustion of the fuel gas at the burner and not for fuel gas to be contained in the fire box.

16. There is a tube rupture in a fired heater causing a fire (contained in the heater) resulting in greater than $25,000 

in damages to the heater internals (beyond that of replacing the failed tube). The tube failure is a loss of primary 

containment of the process fluid and combined with the additional damages greater than $25,000 makes this a 

reportable PSI. 

ACUTE RELEASES 

17. There is a 10 bbl spill of gasoline (1400 kg, 3100 lbs.) that steadily leaked from piping onto soil over a two-week 

time period. Simple calculations show the spill rate was approximately 0.03 bbls per hour (9 lbs./hr). This is not 

a reportable PSI since the spill event was not an "acute" release (e.g., the 1000 kg (2200 lbs.) threshold exceeded 

in any 1 hour period).

18. Same example as above, except that the 10 bbl leak was estimated to have spilled at a steady rate over a period of 

1 hour and 30 minutes. Simple calculations show that the spill rate was 6.7 bbls (933 kg or 2060 lbs.) per hour. 

The spill rate was slightly less that the reporting threshold of 1000 kg (2200 lbs.) within any "1 hour" period, and 

therefore is still not a reportable PSI.

19. While troubleshooting a higher-than-expected natural gas flow rate, operating personnel find a safety valve on 

the natural gas line that did not reseat properly and was relieving to the atmospheric vent stack through a knockout drum. Upon further investigation, it is determined that a total of 1 Million lbs of natural gas was relieved 

at a steady rate over a 6 month period. This is not a reportable PSI as the release rate (~100 kg per hour) is not 

“acute”, (i.e. does not exceed the 500 kg TQ for flammable vapors in any 1 hour time period).

Note: This size release may be reportable under environmental regulations.

20. An operator discovers an approximate 10 bbl liquid spill of aromatic solvent (e.g. benzene, toluene) near a process exchanger that was not there during his last inspection round two hours earlier. Since the actual release duration is unknown, a best estimate should be used to determine if the TQ rate has been exceeded (it is preferred 

to err on the side of inclusion rather than exclusion). This incident is a PSI because the solvents involved are 
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Packing Group II materials and the threshold quantity of 7 bbl is exceeded if the time period is estimated to be 

less than one hour.

DOWNSTREAM DESTRUCTIVE DEVICES (e.g., flares, scrubbers, incinerators, quench drums)

21. The flare system is not functioning properly due to inactive pilots on the flare tip. During this time, a vapor load 

is sent to the flare due to an overpressure in a process unit. The volume of the vapor through the pressure relief 

device is greater than the threshold and it results in the formation of a flammable mixture at grade. This would be 

classified as a PSI since the relief valve discharge is greater than the threshold quantity and resulted in an unsafe 

release.

22. 100 bbl of naphtha liquid are inadvertently routed to the flare system through a pressure relief device. The flare 

knockout drum contains most of the release; however, there is minimal naphtha rainout from the flare. This is a 

PSI since the volume released from the pressure relief device to a downstream destructive device does exceed the 

threshold quantity and resulted in one of the four listed consequences (i.e. liquid carryover).

23. A pressure relief device release less than threshold quantity is routed to a scrubber which is overwhelmed by a 

flow rate greater than design and exposes personnel to toxic vapors resulting in a days away from work injury. 

This is a PSI since an loss of primary containment resulted in a days away from work injury. The rules for pressure relief device discharges are superseded by the actual harm caused.

24. A propane tank over-pressures through a pressure relief device to the flare system. The pilots on the flare system are not working properly, and the flare does not combust the vapors. The event transpires over a period of 

45 minutes. The volume of propane release was estimated to be 1300 pounds and the release dissipated into the 

atmosphere above grade and above any working platforms. Even though the release exceeded the threshold quantity, this is not a PSI since the discharge was routed to a downstream destructive device with none of the listed 

consequences.

25. An upset causes a pressure relief device to open and release fuel gas to the facility flare system. The flare system 

works properly and combusts the vapor release which came from the pressure relief device. This is not a PSI 

since the pressure relief device release was routed to a downstream destructive device that functioned as intended 

(i.e. did not cause one of the four listed consequences).

SAFETY RELIEF DEVICE / SYSTEM

26. There is a unit upset and the relief valve opens to an atmospheric vent which has been designed per API Standard 

521 for that scenario, resulting in a gas release to the atmosphere with no adverse consequences. This would 

not be a reportable PSI since vapors and gases released to atmosphere from safety valves, high-pressure rupture 

disks, and similar safety devices that are properly designed for that event per API Standard 521 or equivalent 

are excluded, as long as the release did not result in liquid carryover, discharge to a potentially unsafe location, 

an on-site shelter-in-place, or public protective measures (e.g. road closure) and and a PRD discharge quantity 

greater than the threshold quantity.

27. A chlorine vessel has a Pressure Relief Device (PRD) that was identified in a recent PHA to be undersized. In the 

process of making a transfer, the vessel overpressures. A release of 60 pounds of chlorine gas (TIH Zone B material) occurs through this PRD to a safe location over a period of 25 minutes. This would not be a Tier 1 or Tier 2 

PSE, regardless of the HAZOP finding, so long as it did not result in a liquid carryover, on-site shelter-in-place, 

public protective measure or other indication of discharge to an unsafe location.
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28. There is a unit upset and the relief valve fails to open, resulting in overpressure of the equipment and an "acute" 

release of flammable gas from a leaking flange. The amount released is above the 500 kg (within 1 hour) threshold. 

This is a reportable PSI. Releases from flanges are not excluded from PSI reporting.

TOXIC GAS, VAPOR OR AEROSOL

29. A leak on a high pressure hydrochloric acid line results in a spill of 1900 lbs of hydrochloric acid. Flash calculations 

indicate that greater than 220 lbs. of hydrogen chloride would be released as a vapor. The 1900 lbs release of hydrochloric acid is not a reportable PSI since this liquid is categorized as a “Packing Group II” corrosive liquid, with a 

2200 lbs reporting threshold. However, since the liquid flashed or was sprayed out as an aerosol, producing more 

than 220 lbs of hydrogen chloride as vapor the event would be reportable due to exceeding the 100 kg (~220 lbs) or 

more of Toxic Inhalation Hazard Zone C material within 1 hour.

30. A pipe containing CO2 and 10,000 vppm (1% by volume) H2S leaks and 7,000 kg (15,400 lbs) of the gas is released 

within a short time period (e.g., less than one hour). Calculations show that the release involved about 55 kg (120 lbs) 

of H2S. The release is a reportable PSI since the reporting threshold for Toxic Inhalation Hazard Zone B chemicals is 

any amount greater than 25 kg (55 lbs) of the toxic chemical (e.g., H2S). 

31. Same as above, except that the H2S concentration in the pipe is 50 vppm, rather than 10,000 vppm. The incident 

would still be reportable as a PSI since the release of CO2 is greater than the 2000 kg (4400 lb) threshold.

DAYS AWAY FROM WORK INCIDENTS

A ”days away from work” incident (or fatality) inclusion as a reportable Process Safety Incident depends upon 

it being caused by the loss of containment of a material or is directly related to evacuating from or responding 

to the loss of containment..

32. .An operator is walking, then slips and falls to the floor and suffers a lost time injury. The slip/fall is due to weather 

conditions, "chronic" oily floors and slippery shoes. This is not a reportable PSI. Personnel safety "slip/trip/fall" incidents that are not directly associated with evacuating from or responding to a loss of containment incident are specifically excluded from PSI reporting.

33. Same as above, except that the operator slipped and fell while responding to a small flammable liquid spill (e.g., less 

than 1000 kg in 1 hour). This would be PSI reportable since the operator was responding to a loss of containment 

incident. A PSI is reportable if the loss of primary containment occurs on Company Premises and results in a lost 

time incident or fatality. For fatalities and lost time incidents, there is no release threshold quantity requirement.

34. Same as above, except that the operator slipped and fell several hours after the incident had concluded. This would 

not be PSI reportable. The terms "evacuating from" and "responding to" in the reporting exclusion mean that the loss 

of containment and associated emergency response activities are on-going. Slips/trip/falls after the event have concluded (such as "after-the-fact" clean-up and remediation) are excluded from PSI reporting.

35. A scaffold builder suffers a lost time injury after falling from a scaffold ladder while evacuating from a loss of containment incident on nearby equipment. This is a reportable PSI.

36. An operator walks past an improperly designed steam trap. The steam trap releases and the operator's ankle is burned 

by the steam, resulting in a lost time injury. This is a reportable PSI because even though the loss of containment was 
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steam (vs. hydrocarbon or chemical), the physical state of the material was such that it caused a lost time injury. 

Non-toxic and non-flammable materials are excluded from the threshold quantity criteria, but are subject to the 

other consequence criteria.

37. An enclosure has been intentionally purged with nitrogen. A contractor bypasses safety controls, enters the enclosure and dies. This is a reportable fatality, but not a reportable PSI since there was no unplanned or uncontrolled 

loss of primary containment. 

Note: This fatality may be reportable under safety regulations and may need to be recorded on a company’s 

injury and illness log.

38. Same as above, except that nitrogen inadvertently leaked into the enclosure. This would be a reportable PSI (and 

fatality) since there was a fatality associated with an unplanned loss of primary containment.

39. An operator responding to an H2S alarm collapses and has a “days away from work” injury. If the alarm was 

triggered by an actual unplanned or uncontrolled H2S LOPC, the event would be a reportable PSI. If the alarm 

was a false alarm, the event would not be a reportable PSI because there was no actual release.

PIPELINES

40. An underground pipeline leaks and releases 1,000 bbls of diesel (combustible material) over 3 days (13.9 bbl/

hr).. The spill results in contaminated soil that is subsequently remediated. This is not a reportable PSI since 

there were no safety consequences and the quantity did not exceed the . "acute" threshhold of 14 bbls or greater. .

41. A pipeline leaks and releases 2000 lbs. of flammable vapor above ground within 1 hour. However, the release 

occurred in a remote location within the site. The release is PSI reportable, since "remoteness" is not a consideration and it release exceeds the threshold quantity.

42. A DOT covered pipeline that is owned, operated, and maintained by Company A crosses through Company B’s 

property. The DOT covered line has a 1500 lb release within an hour from primary containment of flammable gas 

and causes a fire resulting in greater than $25,000 damage to Company A’s equipment. This is not a reportable 

PSI for Company B since the pipeline is not owned, operated or maintained by Company B. This would be a 

transportation incident for Company A.

FIRES or ENERGY RELEASES NOT ASSOCIATED WITH LOSS OF PRIMARY CONTAINMENT

As a general rule, a fire or energy release is reported as a PSI only if caused by a loss of primary containment or 

results in a chemical release in excess of the reporting quantities. Examples include:

43. An electrical fire impacts the operation of the process resulting in the release of 4000 lbs. of toluene. This event 

would be reported as a PSI since if the loss of primary containment exceeds the 2200 lb. reporting threshold for 

toluene.

44. An electrical fire, loss of electricity, or any other loss of utility which causes a plant shutdown and possibly 

incidental equipment damage greater than $25,000 (e.g., damage to reactors or equipment due to inadequate 

shutdown) but does not cause a loss of primary containment that results in one of the identified consequences 

would not be reported as a PSI. To be a reportable PSI, there must be a loss of primary containment.
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45. A bearing fire, lube oil system fire, electric motor failure, or similar fire occurs which damages the equipment 

(> $25,000) but does not cause a loss of primary containment that results in one of the identified consequences 

would not be reported as a PSI since no chemical release greater than the threshold quantity or injuries occurred.

46. .If in the examples #44 or #45, if either an injury or chemical release exceeding the threshold quantity had 

occurred these would have been reportable PSI events.

47. An internal deflagration in a vessel causes equipment damage > $25,000, but there was no loss of containment. 

While this is a serious process event and should be investigated as such, it does not meet the definition of a 

reportable PSI since there was no loss of primary containment.

48. The vent on a storage tank containing chemicals becomes plugged and vacuum caused by routine pump out 

collapses the tank resulting in equipment damages >$25,000. This event would not be reported as a PSI since 

there was no loss of primary containment.

49. If in the example #48, if a tank seam failed resulting in a spill of contents in excess of the TQ quantity for that 

material, it would have been reported as a PSI (even if the contents were captured in secondary containment 

dikes).

50. A scaffold board is placed near a high pressure steam pipe and subsequently begins to burn, but is quickly 

extinguished with no further damage. The investigation finds that the board had been contaminated by some oil, 

but there is no indication of an oil leak in the area. This is not a reportable PSI since there was no unplanned or 

uncontrolled LOPC.

MARINE TRANSPORT VESSELS

51. A company operated Marine Transport Vessel has an onboard "acute" spill of combustible material greater than 

14 bbls. The event is not PSI reportable since Marine Transport Vessel incidents are specifically excluded, except 

when the vessel is connected to the process for the purposes of feedstock or product transfer.

52. A third-party barge is being pushed by a tug and hits the company dock. A barge compartment is breached and 

releases 50 bbl of diesel to the water. The event is not a reportable PSI since the marine vessel was not connected 

to the process for the purposes of feedstock or product transfer..

TRUCK AND RAIL

53. A company railcar derails and spills more than 7 bbls of gasoline while in transit outside the facility. The incident 

is not PSI reportable since railcar was connected to the process for the purposes of feedstock or product transfer 

or being used for onsite storage.

54. A third-party truck/trailer overturns while in the Company Premises, resulting in an "acute" spill of gasoline 

greater than 7 bbls. The incident is not reported as a PSI reportable if the truck is no longer connected to the 

loading/unloading facilities. However, companies may choose to have transportation incident metrics, which 

would capture this event.

55. A contract truck hauler is unloading caustic and the hose separates and generates an airborne aerosol and/or 

liquid caustic spill of 2500 kg. The event is a reportable PSI since the caustic TQ of 1000 kg was exceeded and 
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the truck was still connected to the loading/unloading facility immediately prior to the incident.

56. Two chlorine railcars have been delivered to the facility. One is connected to the process and the other is staged 

at the unloading rack but is not connected to the process. While at the unloading rack but not connected to the 

loading rack, the second railcar develops a leak and 6 lb is released in less than an hour. This is not a reportable 

PSI since truck and railcars are expressly excluded unless connected to the process or being used for on site 

storage. Staging while waiting to unload is not considered storage.

OFFICE BUILDING

57. There is a boiler fire at the Main Office complex, and direct cost damages totaled $75,000. The incident is not 

PSI reportable since Office Building incidents are specifically excluded.

MAN-MACHINE INTERFACE INCIDENTS

58. An operations technician is injured while working around the finishing equipment in a polymers plant. The injury 

is caused by the mechanical, man-machine interface with the equipment. This would not be a reportable Process 

Safety Incident because there was no unplanned or uncontrolled loss of containment.

ASSIGNMENT OF SEVERITY SCORES

59. A leak on a high pressure hydrochloric acid line results in a spill of 4000 lbs of hydrochloric acid. Flash 

calculations indicate that greater than 500 lbs. of hydrogen chloride would be released as a vapor. Three 

employees in the plant received inhalation injuries, resulting in hospitalization for multiple days. The toxic 

cloud was witnessed by emergency response crews to extend into adjacent plants within the site, but there was 

no evidence that a harmful toxic concentration extended beyond the plant fenceline. However, a precautionary 

shelter-in-place and closure of adjacent interstate highway occurred for 2 hours. Resulting in extensive local 

media coverage and brief national media coverage. This incident clearly is a reportable PSI incident since the 

Hydrochloric acid and HCI vapors released each exceeded the chemical release TQ. Furthermore, the injuries to 

employees exceeded the health effects threshold for reporting. The Safety/Human Health severity level is a “2” 

(9 severity points) due to multiple lost-time injuries; the Fire/Explosion severity level is “N/A” (0 severity points) 

due to no equipment damages or clean-up costs greater than $25,000; the Potential Chemical Impact severity 

level is a “3” (3 severity points) since the chemical release extended outside of containment but retained on 

company property; and the Community/Environmental Impact severity level is a “2” (9 severity points) due to the 

shelter-in-place and media attention. The maximum of the four categories was a Severity level “2”; therefore, 

the overall incident could be classified as a Severity Level “2” PSI. The Severity points which would be used in 

the Process Safety Incident Severity Rate (PSISR) calculation would be 21 points (9+0+3+9=21). 

60. The release of 10,000 lbs of ethylene (flammable vapor) occurs when a flange on a compressor fails. The 

flammable vapor cloud collects within the compressor building and adjacent pipe rack (i.e., a Potential Explosion 

Site), but fortunately does not ignite. As a precautionary measure, the occupants of the plant and surrounding 

plants are evacuated. But no injuries or substantial damages occur. There is no off-site impact. This incident 

is a reportable PSI incident since the ethylene vapors released exceeded the 1100 lb chemical release TQ for 

a flammable vapor. The Safety/Human Health, Fire/Explosion, and Community/Environmental severity levels 

are each “N/A” (0 severity points) due to none of these impacts of this event exceeding the thresholds for 

classification as a Severity Level “4” for that category. The Potential Chemical Impact severity level is a “2” 

(9 severity points) since the flammable vapor release resulted in a vapor cloud entering a building or potential 
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explosion site (congested/confined area) with potential for damage or casualties if ignited. The maximum of the 

four categories was a Severity level “2”; therefore, the overall incident could be classified as a Severity Level 

“2” PSI. The Severity points which would be used in the Process Safety Incident Severity Rate (PSISR)

calculation would be 9 points (0+0+9+0=9). 

61. The release of 10,000 lbs of ethylene (flammable vapor) occurs when a flange on a compressor fails. The 

flammable vapor cloud collects within the compressor building and adjacent pipe rack and ignites. The resulting 

vapor cloud explosion causes $30MM in damages or other direct costs, severely injures 3 employees (i.e., the 

injuries each meet the definition of “lost time injury”), and gains regional media attention for several days. The 

Safety/Human Health severity level of this event meets the threshold for classification as a Severity Level “2” (9 

severity points) due to the multiple lost time injuries, the Fire/Explosion severity level would be classified at the 

Severity Level “1” (27 severity points), the Potential Chemical Impact severity level is a “2” (9 severity points) 

since the flammable release resulting in a vapor cloud entering a potential explosion site (congested/ confined 

area) as demonstrated by the results, and the Community/ Environmental severity level meets the threshold for 

classification as Severity Level “2“ (9 severity points) due to the media coverage. The maximum of the four 

categories was a Severity level “1”; therefore, the overall incident could be classified as a Severity Level “1” PSI. 

The Severity points which would be used in the Process Safety Incident Severity Rate (PSISR) calculation 

would be 54 points (9+27+9+9=54). A company could argue that the potential chemical impact severity level for 

this even should be “N/A” (0 points) since much of the fuel is consumed in the explosion. However, since there 

is a potential that all fuel was not consumed and/or the event could have been even more significant under slightly 

different circumstances – the Potential Chemical Impact severity level of “2” (9 severity points) is appropriate. 

MIXTURES

62. A chemical manufacturer spills 10,000 lbs of a formulated product containing multiple chemicals downstream of 

a mixing operation. This material is marketed as specific product (e.g., a heating fluid, brake fluid, etc.). Since 

this material is shipped in this formulation, the company has previously evaluated the mixture per all of the UN 

Dangerous Goods definitions (or DOT regulations in the USA) and classified the mixture as a “Packing Group 

III” material. Since the spill exceeded the 2000 kg (4400 lb.) threshold quantity of a Packing Group III material, 

this spill would be reported as a PSI. 

63. A pipe fitting in a specialty chemicals plant fails, releasing 4000lb of a mixture of 30% formaldehyde, 45% 

methanol, and 25% water in less than one hour. This mixture is not classified by the UN Dangerous Goods/U.S. 

DOT protocols; therefore, the threshold quantity mixture calculation is applied. The pure component reporting 

threshold of formaldehyde is 4400 lb and methanol is 2200lb. 

 Component wt.% Release Qty PSE TQ % of TQ

 (lb) (lb)

 Formaldehyde 30% 1200 4400 27.3%

 Methanol 45% 1800 2200 81.8%

 Water 25% 1000 n/a 0%

 109.1%

This release is a Tier 1 PSE since the cumulative percentage exceeds 100% even though the individual 

components do not exceed their individual threshold quantities.

Note: This is an alternative shortcut approach and can give more or less conservative results. A more precise 
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approach is to use the rules of DOT 49 CFR 173.2a [14] or UN Recommendations on the Transportation of 

Dangerous Goods, Section 2.

VACUUM TRUCK OPERATIONS

64. After collecting a load from an adjacent unit, a vacuum truck is parked at the wastewater treatment facility 

awaiting operator approval to discharge. While waiting the vacuum truck malfunctions and vents process material 

to the atmosphere. This is not a PSi since vacuum truck operations are excluded unless loading, discharging, or 

using the truck’s transfer pump.

65. A vacuum truck outfitted with a carbon canister on the vent is loading a spill of hydrocarbons. The carbon canister 

catches fire which escalates to the point of creating more than $45,000 in damage to the vacuum truck. This is 

a PSI since the original spill of hydrocarbons constitutes the LOPC and the response to the LOPC results in fire 

damage greater than $25,000.

DIRECT COSTS

66. A pump seal fails and the resultant loss of containment catches on fire. The fire is put out quickly with no 

personnel injuries. However, the fire resulted in the need to repair some damaged instrumentation and replace 

some insulation. The cost of the repairs, replacement, cleanup, and emergency response totaled $20,000. This is 

not a PSI. It should be noted the cost of replacing the seal is not included in the direct cost calculation—only the 

costs for repair and replacement of the equipment damaged by the fire, not the cost to repair the equipment failure 

that led to the fire.

OFFICIALLY DECLARED EVACUATION OR SHELTER-IN-PLACE

67. A small quantity of very odorous material enters a cooling water system via tube leak. The material is dispersed 

into the atmosphere at the cooling tower. An elementary school teacher decides not to conduct recess outside due 

to a noticeable odor even though officials deemed no shelter-in-place was necessary; therefore, this is not a PSI.

68. Less than 1 pound of Hydrogen Fluoride gas is released while unloading a truck at a refinery. The release is 

detected by a local analyzer and triggers a unit response alarm. An off-duty police officer living in a nearby home 

advises his neighbors to evacuate because “an alarm like that means there’s a problem at the refinery.” This is 

not an officially declared evacuation or shelter-in-place because in this situation the officer is acting as a private 

citizen suggesting a precautionary measure; therefore this is not a PSI.

II. Leading Metrics

This section contains a number of potential leading metrics. These indicate the health of important aspects of the 

safety management system. If measured and monitored, data collected for leading metrics can give early indication of 

deterioration in the effectiveness of these key safety systems, and enable remedial action to be undertaken to restore the 

effectiveness of these key barriers, before any loss of containment event takes place.
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The safety systems that leading metrics have been developed for are:

 • Maintenance of mechanical integrity;

 • Action items follow-up;

 • Management of change; and

 • Process safety training and competency (and training competency assessment).

It is recommended that all companies adopt and implement leading process safety metrics, including a measurement of 

process safety culture. However, given the number of metrics described below it may be impracticable to collect and 

report data for each of these categories. Companies should identify which of these components are most important for 

ensuring the safety of their facilities, and should select the most meaningful leading metrics from the examples below 

for the identified components, and where significant performance improvement potentially exists. Other leading metrics 

may be defined as well if applicable.

These leading process safety metrics were selected based upon the experience of the organizations 

represented by the work group, including

 • Barriers related to the hazards inherent in their operations, 

 • Barriers related to the critical causal factors or immediate causes of major incidents and high 

 potential near-misses experienced by their operations, and

 • Review of the metrics detailed in the CCPS Risk Based Process Safety book.

These leading metrics will continue to be refined as the CCPS Metric Committee finalizes the Metric Guideline book 

in 2008. Enhancements or suggestions to these metrics are welcome.

A. (Number of inspections of safety critical items of plant and equipment due during the measurement period 

and completed on time/Total number of inspections of safety critical items of plant and equipment due during 

the measurement period) x 100%.

 • This metric is one measure of the effectiveness of the process safety management system to 

 ensure that safety critical plant and equipment is functional.

 • This involves collecting data on the delivery of planned inspection work on safety critical plant and equipment.

 • The calculation of the metric involves

 - Define the measurement period for inspection activity.

 - Determine the number of inspections of safety critical plant and equipment 

 planned for the measurement period.

 - Determine the number of inspections of safety critical plant and equipment 

 completed during the measurement period.

 • Inspections not undertaken during the previous measurement period are assumed to be carried 

 forward into the next measurement period

1.0 Mechanical Intergrity
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Definitions:

Safety critical plant and equipment: Plant and equipment relied upon to ensure safe containment of hazardous 

chemicals and stored energy, and continued safe operation. This will typically include those items in a plant’s preventative maintenance program, such as:

• Pressure vessels

• Storage Tanks

• Piping systems

• Relief and vent devices

• Pumps

• Instruments

• Control systems

• Interlocks and emergency shutdown systems

• Emergency response equipment

B. (Length of time plant is in production with items of safety critical plant or equipment in a failed state, as identified by inspection or as a result of breakdown/Length of time plant is in production) x 100%

This is a metric to determine how effectively the safety management system ensures that identified deficiencies 

of process safety equipment are fixed in a timely manner.

(Number of past due of process safety action items / Total number of action items currently due) x 100%..

This metric may be configured as one aggregate metric or several individual metrics of specific past due items, such as:

• (Number of past due audit action items / total number of audit action items currently due) x 100%

• (Number of past due PHA action items / total number of PHA action items currently due) x 100%

• (Number of past due incident investigation action items / total number of incident investigation action items currently due) x 100%

• (Number of past due PHA action items / total number of PHA action items active or open) x 100%

Definitions:

Currently Due: Actions with a due date less than or equal to the current date.

Past Due: Actions that are active or open and past their assigned completion date.

A. Percentage of sampled MOCs that satisfied all aspects of the site’s MOC procedure.

• This metric measures how closely the site’s MOC procedure is being followed.

• Involves a periodic audit of completed MOC documentation. Steps in conducting the audit:

 - Define the scope of the audit: time frame, frequency, and operating department(s).

 - Determine the desired and statistically-significant sample size. This can be done using 

 widely-available tables, based on the total number of MOC documents in the population.

3.0 Management of Change

2.0 Action Items Follow-up
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 - Review the completed MOC documentation, including backup documentation such as the hazard 

 review and updated Process Safety Information such as operating instructions and P&IDs.

 - Calculate the metric:

 % of MOCs properly executed = 100 x (# of properly executed MOCs) 

 (total # of MOCs)

B. Percentage of identified changes that used the site’s MOC procedure prior to making the change. 

• This metric measures how well a department/site (i) recognizes changes that require use of the site’s MOC 

procedure and (ii) actually makes use of the procedure prior to implementing changes.

• Involves a periodic audit of the changes made in a department/site and a determination of which changes 

required use of MOC. Steps in conducting the audit:

 -Define the scope of the audit: time frame and operating department(s).

 -Identify the types of changes that may have bypassed the site’s MOC procedure, based on how the site’s MOC

 procedure defines changes (see definition below).

 -Identify changes that bypassed the MOC procedure. This can be done by:

 • Reviewing maintenance work orders, 

 • Reviewing documentation from capital and maintenance projects,

 • Reviewing Distributed Control System programming changes, and/or

 • Interviewing department personnel.

 • Calculate the metric:

 % of changes using MOC = 100 x (# of MOCs) 

 (# of MOCs + # of changes that bypassed MOC)

Other Ideas: The two MOC metrics above provide a means by which companies can readily measure how well they 

are identifying changes that need to be evaluated by MOC and how well they are executing the MOCs they do identify. 

Following are ideas companies may want to consider if they want to develop more sophisticated internal MOC metrics:

• A refinement to the metric for how well a company is executing their MOC procedure is to include a grading 

system for how well a given MOC followed the procedure, rather than the yes/no ranking provided above. 

For example, if the company identified 25 key aspects to a properly completed MOC and a given MOC satisfied 20 of these aspects, then the MOC would receive a grade of 0.8. An audit of multiple MOCs could 

generate an overall average grade for the audit sample. An even more sophisticated approach could include a 

relative weighting of the criticality of the, say, 25 aspects to a properly completed MOC.

• A company may desire to have a metric for the number of temporary MOCs not closed out in the prescribed 

time period. Temporary MOCs are typically executed for emergency, start-up or trial situations. The prescribed time period may be specified in the particular MOC or as a maximum allowable duration under the 

site’s temporary MOC procedure. The temporary MOC must be closed out by restoring the system to original 

design condition or by making the change permanent via the site’s regular MOC procedure. Failure to close 

out in a timely fashion could present risks.

• A company may desire to have a metric that measures how effective the site’s MOC procedure is at identifying and resolving hazards related to changes. If so, the following may be considered:
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Percentage of start-ups following plant changes where no safety problems related to the changes were encountered 

during re-commissioning or start-up.

• Involves real-time logging of start-ups, including safety problems encountered during recommissioning and startup, followed by a determination of which problems had a root cause related to a change that was made.

• Involves a periodic audit of completed MOCs that involved a shut-down and restart of a unit or portion of a unit. 

Steps in conducting the audit:

o Define the scope of the audit: time frame and operating department(s).

o Determine the number of start-ups of the unit(s) or portions of the unit(s) following the implementation of changes. 

o Determine the number of these start-ups where a change-related safety problem was encountered after checkout, 

 during the recommissioning or start-up phases.

o Calculate the metric:

% of safe start-ups following changes = 100 x (# of start-ups following changes without change - related safety problems during recommissioning and start-up) / (total # of start-ups following changes)

A complicating factor that must be considered is the fact that problems from the change may not show up until a long time after 

start-up.

Definitions:

Changes requiring MOC review: The types of changes requiring use of the site’s MOC procedure should be defined by the 

procedure. Normally this will include:

- Changes to equipment, facilities and operating parameters outside the limits defined in the unit’s

 Process Safety Information.

- Process control modifications.

- Introduction of new chemicals.

- Changes to chemical specifications or suppliers

- Building locations and occupancy patterns.

- Organizational issues such as staffing levels and job assignments.

Checkout: The phase after a change is made and before the introduction of chemicals and other hazardous materials when system 

integrity is confirmed. Potentially hazardous conditions can be identified and corrected during checkout without resulting in an 

incident.

Recommissioning: The phase after checkout and before start-up when chemicals are introduced to the system and pressures/

temperatures may be increased. Potentially hazardous conditions identified during recommissioning may result in a safety and/

or environmental incident.

Start-up: The phase after recommissioning when production operations are initiated. Potentially hazardous conditions identified 

during start-up may result in a safety and/or environmental incident.
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4.0 Process Safety Training and Competency

A. Training for PSM Critical Positions

(Number of Individuals Who Completed a Planned PSM Training SessionOn-time)/(Total Number 

 of Individual PSM Training Sessions Planned)

Definitions:

PSM Critical Position: Any facility position that includes key activities, tasks, supervision, and/or responsibility for component procedures critical to the prevention of and recovery from major accident events.

Planned PSM Training Session: A specific exercise designed to enhance an individual’s knowledge, skill, 

and/or competency in a PSM critical position for areas that directly influence the prevention of and recovery 

from major accident events. A single individual may have multiple training sessions during a reporting period. A 

single exercise may involve multiple individual training sessions (e.g., a training class with multiple individuals). 

B. Training Competency Assessment

(Number of Individuals Who Successfully Complete a Planned PSM Training Session on the First Try)/ 

(Total Number of Individual PSM Training Sessions with Completion Assessment Planned for that time 

period)

Definitions:

Successful Completion: A passing grade on an exam or competency assessment for which there is no requirement to repeat/redo the training, exam, competency assessment or any part thereof.

Training Session with Completion Assessment: A planned PSM training session for which there is a required 

demonstration of knowledge or skill through an examination or competency assessment.

C. Failure to follow procedures/safe working practices 

(Number of safety critical tasks observed where all steps of the relevant safe working procedure were not 

followed/Total number of safety critical tasks observed) x 100%

To determine by work place observation of tasks identified as being safety critical that have a relevant safe 

operating procedure, whether all of the relevant steps are followed.

5.0 Safety Culture

A mechanism for measuring the effectiveness of process safety culture within chemical process organizations

would be to adopt the use of a cultural survey of the type included as Appendix G of the Baker panel report and

discussed throughout the report used to determine the adequacy of the safety culture at BP’s US refineries.
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The chemical and downstream oil processing sectors should consider use of this or similar survey. If used, the 

safety culture survey should be undertaken in such a way that the results are made anonymous, so that respondent cannot be identified and that there will be no negative judgment on respondents that may affect their willingness to participate or their level of openness.

Undertaking a culture survey of this nature will not enable comparison of results between organizations because 

of the many other factors that can affect the results, but it will be of benefit in determining changes within an 

organization over time.

6.0 Operating & Maintenance Procedures

A. Procedures Current & Accurate

(Number of operating or maintenance procedures reviewed/updated per year / Total number of operating 

or maintenance procedures required to be reviewed/updated during the measurement period) x 100%.

This metric measures the progress of the review/update cycle. A downward trend may indicate that more attention or resources are needed to maintain procedures.

B. Procedures Clear, Concise & Include Required Content

(Number of operating or maintenance procedures reviewed for content / Total number of operating or 

maintenance procedures) x 100%.

This metric measures the progress of creating clear, concise, and effective operating and maintenance procedures. 

A checklist of procedure criteria will need to be developed that addresses:

• Document control

• Action steps that are clear and properly ordered

• Cautions, Warnings, and Notes

• Safe operating limits, consequences of deviations from limits, and steps to take to maintain the process 

within the safe operating limits

• Limiting conditions for operation

• Checklists (where appropriate)

C. Confidence in Procedures

(Number of operators or maintenance technicians who believe that procedures are current, accurate, and 

effective / Total number of operators or maintenance technicians affected by the procedures) x 100%.

Results of opinion surveys of operators or maintenance technicians my provide early indication of changes in the 

accuracy or effectiveness of procedures. The survey should identify concerns about time required to update procedures, accuracy, and user friendliness.
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7.0 Fatigue Risk Management

A. Fatigue Risk Education

(Number of affected employees educated on the causes, risk and potential consequences of fatigue / Total 

number of affected employees) x 100%.

The education should acquaint all affected employees with the basic scientific principles of sleep, sleep disorders, 

alertness, circadian, and fatigue physiology so that they can make informed decision which will help them reduce 

the fatigue risk for themselves, their colleagues, and the people they may supervise or manage. This education 

should also provide information designed to increase family member awareness of how they can help the affected 

employee keep alert, safe and healthy.

B. Percentage Overtime (median, mean, top 10 %)

(Number of overtime hours / Total number of standard work hours during the measurement period) x 

100% per person.

C. Number of Extended Shifts

Number of extended shifts per person during the measurement period

Extended shifts are time an employee is assigned to work that extends outside their regularly scheduled shift hours 

and into other shifts. Extended shifts include holdovers to participate in training, safety meetings, and the like. It 

does not include time needed for normal shift handoff.

III. Near Miss Reporting and other Lagging Metrics

The CCPS committee recommends that all companies implement a Near Miss reporting metric(s). Since a near miss is 

an actual event or discovery of a potentially unsafe situation, this metric could be defined as a “lagging” metric. A large 

number or increasing trend in such events could be viewed as an indicator of a higher potential for a more significant 

event; therefore, many companies use Near Miss metrics as a surrogate for a “Leading” metric. Many companies have 

discovered that an increasing trend in near misses reported, at least for the first several months after implementation, is 

a positive sign of improved culture and process safety awareness by the organization. Therefore, it is quite possible that 

the number and count of more significant incidents decrease as the number of near misses reported increase.

It is important that all companies have some type of near miss reporting system implemented. The metric and definitions described below (created by harmonization of definitions used by contributing companies) should be considered 

if implementing a new system. If a company already has an effective near miss reporting system, which includes or 

aligns well with the following definitions, there should be no reason to replace that existing system.

It is recommended that all companies have an internal metric to report all Losses of Primary Containment (LOPC) 

and unplanned fires/flames. This will include all pressure relief device discharges excluded from the industry lagging 

metric. For the purposes of the industry-wide process safety incident lagging metric, a threshold value has been 

established for events that should be reported as part of that metric. Companies should have additional metrics, or 
36

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PS

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Process Safety Leading and Lagging Metrics

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include within their overall “Near Miss” metric, any additional LOPC or unplanned fires/flames which fell below 

the PSI or PSE – Tier 2 threshold and were not recorded in the industry-wide lagging metrics. There are important 

learning values from recording and investigating these events.

A "near miss" has three essential elements. While various wordings for a near miss definition are used within 

industry, the overwhelming majority has these elements:

• an event occurs, or the discovery of a potentially unsafe situation;

• the event or unsafe situation had reasonable potential to escalate, and

• the potential escalation would have led to adverse impacts.

For purposes of this discussion, the following near miss definition is used.

Near Miss: An undesired event that under slightly different circumstances could have resulted in harm to people, 

damage to property, equipment or environment or loss of process. 

This near miss definition may be applied to any aspect of an EHS management program, used for reporting environmental, personnel safety or process safety near misses for example.

Definition of a Process Safety Near Miss

In order to specifically focus on process safety in a near miss reporting program, many companies have also developed 

a definition for a process safety near miss. Again, for purposes of this discussion, the following process safety near 

miss definition is used.

Process Safety Near Miss:

• any significant release of a hazardous substance that does not meet the threshold for a "Process Safety 

Incident” lagging metric, or

• a challenge to a safety system, where:

Challenges to a safety system can be divided into the following categories:

• Demands on safety systems (pressure relief devices, safety instrumented systems, mechanical 

shutdown systems),

• Primary containment inspection or testing results outside acceptable limits

• Process deviation or excursion.

Examples of Process Safety Near Miss

Near misses for Demands on Safety Systems may fall into a category of either creation of a demand with successful 

safety system operation or creation of a demand with failure of the safety system given a legitimate demand. 

Examples include:

• Opening of a rupture disc, a pressure control valve to flare or atmospheric release, or a pressure safety valve 

when pre-determined trigger point is reached.

• Failure to open of a rupture disk, a pressure control valve to flare or atmospheric release, or a pressure safety 

valve when the system conditions reac h or exceed the prescribed trigger point.

• Activation of a safety instrumented system when “out of acceptable range” process variable is detected. 

 - activation of high pressure interlock on polyethylene reactor to kill reaction/shut off feed

 - compressor shutdown from a high level interlock on the suction knockout drum

• Any time a safety instrumented system fails to operate as designed when a demand is placed on the system (i.e. 

unavailability on demand).
37

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• The number of times a mechanical shutdown system is called upon to function by a valid signal whether or not 

the device actually responds.

Mechanical shutdown systems that are configured for equipment protection with no related loss of containment 

protection should be excluded from the process safety near miss count.

Near misses involving primary containment inspection or testing results outside acceptable limits:

An inspection or test finding that indicates primary containment equipment has been operated outside acceptable 

limits. These findings typically trigger an action, such as replacement-in-kind, repairs to restore fitness-for-service, 

replacement with other materials, increased inspection or testing, or de-rating of process equipment. Examples 

include:

• An inspection or test finding that indicates vessels, atmospheric tanks, piping, or machinery when previous 

operating pressures or levels exceed the acceptable limits based upon wall thickness inspection measurements.

A single event is recorded for each pressure vessel or atmospheric tank regardless of the number of individual 

test measurements found to be below the required wall thickness.

A single event is recorded for each pipe circuit regardless of the number of individual test measurements below 

its required wall thickness as long as it is the same line, constructed of the same material, and is in the same 

service.

Near misses involving a process deviation or excursion include:

• Excursion of parameters such as pressure, temperature, flow outside operating window but remaining within 

the process safety limits.

• Excursions of process parameters beyond pre-established critical control points or those for which emergency 

shutdown or intervention is indicated.

• Operation outside of equipment design parameters.

• Unusual or unexpected runaway reaction whether or not within design parameters.

Near Misses associated with Management System Failures/Issues:

These types of observations should be captured to understand where there are opportunities for improving a facility's process safety management systems. 

Discovery of a failed safety system upon testing

• Relief devices that fail bench tests at setpoints

• Interlock test failures

• Uninterruptible power supply system malfunctions

• Fire, gas, & toxic gas detectors found to be defective during routine inspection/testing

• During inspection of an emergency vent line header, the header was found to be completely blocked with iron 

scale because moisture from the emergency scrubber had migrated back into the header

• During testing of an emergency shutdown system, a Teflon-lined emergency shutdown valve was found stuck 

open because the Teflon had cold flowed and jammed the valve

• During inspection of a conservation vent, found the vent blocked by process material that had condensed and 

frozen
38

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Discovery of a defeated safety system

• Process upset with interlock in bypass condition,

• Defeated critical instrument / device not in accordance with defeat procedure

• Bypasses left on after leaving block valve site

“Errors of Omission / Commission”

• Failure to remove line blanks in critical piping or failure to introduce the correct batch ingredients in the 

proper sequence 

• During replacement of a rupture disk, the disk was found with the shipping cover still in place

• Process control engineer accidentally downloaded the wrong configuration to a process unit DCS

Unexpected / Unplanned Equipment Condition

• Equipment discovered in "unexpected" condition due to damage or premature / unexpected deterioration 

• Wrong fittings used on steam system

• Failure of equipment like heat exchanger tubes leading to mix up and / or contamination of fluids

Physical Damage to Containment Envelope

• Dropping loads / falling objects within range of process equipment

• Truck backed into wellhead

• Snow plow grazed gas line

Maximizing Value of Near Miss Reporting

Near miss reporting provides valuable data for improving the process safety management systems at a facility. The 

following processes can maximize the benefits from a process safety near miss program.

➢ Use process safety lagging indicator, process safety near miss, and management system leading indicators to 

 build a process safety performance pyramid. 

➢ When evaluating process safety near misses, consider the potential adverse impacts. The level of response to 

 a near miss (i.e. investigation, analysis, and follow-up) should be determined using the potential as well as the 

 actual consequences of the event.

➢Tie the near miss data to the deficient management system in order to drive system improvements from near 

 misses as well as from actual incidents.

➢ Place value upon reporting near misses. Consider reward / recognition for reporting near misses as well as 

 rewards for bottom line performance.

Appendix A: UN Dangerous Goods Classification 

and Listing of Chemicals

A comprehensive listing of chemicals, along with the threshold values for reporting as defined by this metric will be 

posted on the CCPS web site: http://www.aiche.org/ccps/resources/metricsproject

Additional information regarding the UN Dangerous Goods Classification System can be found at the 

following web sites:

UNECE web site: 
39

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 http://www.unece.org/trans/danger/publi/adr/adr2007/07ContentsE.html

The PDF Dangerous Goods list complete with UN numbers: 

 http://www.unece.org/trans/danger/publi/adr/adr2007/English/03-2%20E_tabA.pdf

Alphabetical cross reference: 

 http://www.unece.org/trans/danger/publi/adr/adr2007/English/03-3%20E_alphablist.pdf 

UN or DOT definitions

UN DG criteria

Flammable Liquids

Packing Group Flash Point (closed-cup) Initial boiling point

 I – ≤ 35 oC (≤ 95 oF)

 II < 23 oC (< 73 oF) >35 oC (> 95 oF)

 III ≥23 oC ≤ 60 oC (≥ 73 oF ≤ 140 oF >35 oC (> 95 oF) 

Toxic Liquids

TIH Hazard Zones A, B, C and D per US DOT regulations (Note: UN Dangerous Goods definitions do 

not include these definitions, but the following do align with definitions in the UN GHS definitions).

Hazard Zone Inhalation toxicity

A LC50 less than or equal to 200 ppm

B LC50 greater than 200 ppm and less than or equal to 1,000 ppm

C LC50 greater than 1,000 ppm and less than or equal to 3,000 ppm

D LC50 greater than 3,000 ppm or less than or equal to 5,000 ppm

Toxic Liquids

Packing Group Oral toxicity Dermal toxicity Inhalation toxicity by dusts and mists 

 LD50(mg/kg) LD50(mg/kg) LC50(mg/L)

 I ≤ 5.0 ≤ 50 ≤ 0.2

 II > 5.0 and ≤ 50 > 50 and ≤ 200 > 0.2 and ≤ 2.0

 III > 50 and ≤ 300 > 200 and ≤ 1,000 > 2.0 and ≤ 4.0
40

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The packing group and hazard zone assignments for liquids based on inhalation of vapors shall be in accordance with 

the following table:

 Packing group Vapor concentration and toxicity

I (Hazard Zone A) V ≥ 500 LC50and LC50≤ 200 mL/M3

I (Hazard Zone B) V ≥ 10 LC50; LC50≤ 1,000 mL/m3; and the criteria for Packing Group I, 

 Hazard Zone A are not met

 II V ≥ LC50; LC50≤ 3,000 mL/m3; and the criteria for Packing Group I, 

 are not met

 III V ≥ .2 LC50; LC50≤ 5,000 mL/m3; and the criteria for Packing Groups I 

 and II, are not met

Note 1: V is the saturated vapor concentration in air of the material in mL/m3at 20 °C and standard 

 atmospheric pressure.

10,000

1.000

100

10

0 10 100 1,000 10,000 100,000 1,000,000

Hazard Zone A

Hazard Zone B

Hazard Zone C

Hazard Zone D

Division 6.1 Liquids Division 2.3 Gases

Volatility ml/m3

LC50ml/

m3

Packing Group III

Packing Group II

Packing Group I

Hazard Zone B

Packing Group I

Hazard Zone A

Inhalation Toxicity: Packing Group and Hazard Zones
41

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Appendix B: Additional Clarifications regarding UN Dangerous 

Goods lists & Exceptions

The CCPS Committee, working in conjunction with representatives of several chemical and petroleum trade associations and process safety consortiums, selected the UN Dangerous Goods criteria for differentiating chemicals into a 

few threshold quantity categories since this approach:

was comprehensive, aligns with the new Globally Harmonized System of Classification and Labeling of Chemicals 

(GHS), and resulted in excellent differentiation of hundreds of chemicals into a few groupings that aligned well with 

perceived risk when toxicity, flammability, and volatility were considered. 

However, the UN DGL does contain a few materials that are either:

• not of general concern from a petrochemical process safety perspective (e.g., Cotton); 

• described as a generic category with the associated label “not otherwise specified” (n.o.s.) which may require 

further evaluation to assign to a specific chemical (e.g., “Amines, liquid, corrosive, n.o.s.”, or “Hydrocarbons, 

liquid, n.o.s.”); or

• may contain chemicals in a specific physical property state (e.g., “Nitrogen, compressed”, or “Nitrogen, cryogenic liquid”) which may be confused for a less hazardous state which is not designated under the UN DGL. 

[Note: an acute and unintended release of “compressed” or “cryogenic” Nitrogen, Argon, or Helium would be 

treated as a PSI if the release exceeds the 2000 kg (4400 lb.) threshold quantity. But the planned, controlled, 

slow, and safe, releases of these chemicals (e.g., nitrogen used for purging ) would not be reportable.

Furthermore, there are many low hazard materials which are excluded (e.g., solid polyethylene pellets); therefore, are 

not subject to reporting under this metric. However, it may not be apparent to the user if those chemicals are intentionally excluded or if covered under the generic categories described above.

Overall, the benefits of this expanded list of chemicals considered in the CCPS Lagging Metric due to the UN DGL 

outweigh the negatives of potential initial complexity in training or interpretation of these definitions. However, it is 

likely that initially there will need to be interpretations or exceptions for some specific chemicals listed in the UN 

DGL. To maintain the consistency in reporting between companies or trade groups, it is recommended that communication and collaboration between the trade groups continue with regard to any interpretations or exceptions needed 

to facilitate consistent and efficient reporting of the process safety lagging metric. If trade groups mutually agree to 

exclude specific chemicals from the metric, or apply other implementation guidelines, they are encouraged to communicate their decision to CCPS. CCPS can collect and post those agreed exceptions on the web site where these 

metrics documents will be available.
42

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PS

An AIChE Technology Alliance

Center for Chemical Process Safety

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Process Safety Leading and Lagging Metrics

You Don’t Improve What You Don’t Measure
43

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please visit www.ccpsonline.org
CENTER FOR CHEMICAL PROCESS SAFETY

AIChE 3 Park Avenue, New York, New York 10016-5991 USA ■ Tel: (+1) 646.495.1370

www.ccpsonline.org ■ e-mail: ccps@aiche.org

If your company is interested in process 

safety metrics and strengthening its 

process safety program, you should also:

The Global Community Committed to Process Safety

CCPS

An AIChE Technology Alliance

Center for Chemical Process Safety

•	 Join CCPS

	 	 Strengthen Your Corporate Process Safety Culture

Contribute to the Overall Safety of the Industry

Join CCPS, the Global Community Committed to Process Safety

 For information about membership, call +1.646.495.1371 Or email ccps@aiche.Org

 For a complete member list, please see www.Aiche.Org/ccps/about/members.Aspx

• Read “Guidelines for Process Safety Metrics” 

For more information, please see www.wiley.com/go/CCPS

• Attend the Global Congress on Process Safety

For more information, please see www.aiche.org/GCPS

• Read and share the “Process Safety Beacon”

For more information, please see www.aiche.org/CCPS/Publications/Beacon/index.aspx

• Advance basic awareness of Process Safety with the Process Safety Boot Camp

For more information, please see www.aiche.org/ccps/Education/BootCamp.aspx