Implementation guidelines for Environmental Emergency Regulations: appendix 9

Appendix 9: summary of risk evaluation framework methodology for determining thresholds for environmental emergency plans

Acronyms in the risk evaluation framework

acute exposure guideline level


bioaccumulation factor

bioconcentration factor

boiling liquid expanding vapour explosion

Canadian Environmental Protection Act, 1999

Concise International Chemical Assessment Documents

Conseil pour la réduction des accidents industriels majeurs / Major Industrial Accidents Reduction Council

environmental emergency

United States Environmental Protection Agency

Emergency Response Planning Guidelines - 2

International Agency for Research on Cancer

immediately dangerous to life or health

octanol-water partition coefficient

lethal concentration in air where 50% of test species die

lowest reported lethal concentration in air at which death occurred

median lethal dose where 50% of test species die via any exposure other than air

Major Industrial Accidents Council of Canada, now defunct

U.S. National Fire Protection Association

Organisation for Economic Co-operation and Development


persistence, bioaccumulation and toxicity

Process Hazard Analysis Software Tools

Risk Evaluation Framework

risk management program

Toxic Release Inventory

Toxic Substances Management Policy

Hazards evaluated by the risk evaluation framework

To decide whether a substance is potentially hazardous to humans or the environment, the Risk Evaluation Framework (REF) determines whether the substance is:

In each REF category (environmental, human and physical), a trigger is assigned when certain characteristics of the substance are capable of causing harm to humans and/or the environment. A trigger is a qualifier for an E2 plan if it is accompanied by a threshold quantity. These criteria are listed in Table 1.

Table 1: summary of trigger criteria
Hazard rating category Criterion Trigger value
Physical Vapour cloud explosion Flash point < 23°C and Boiling point < 35°C
Physical Reactivity Based on expert opinion Materials that in themselves are readily capable of detonation or of explosive decomposition or explosive reaction at normal temperatures and pressures. This degree should include materials that are sensitive to mechanical or localized thermal shock at normal temperatures and pressures. Also potential for boiling liquid expanding vapour explosion (BLEVE); check if the substance has a spill history of causing deaths.
Human Inhalation toxicity (in order of priority) Final AEGL-02 (30 min) or
IDLH (30 min) or
ERPG-2 (1 h) or
LC50 × 0.1 or
LCLo or
LD50 × 0.01 or
LDLo × 0.1
Vapour pressure ≥ 10 mm Hg
Human Human and animal carcinogenicity IARC rating: 1, 2A or 2B
EPA rating: A, B1 or B2
Persistence in any media < 5 years
Environmental Acute aquatic toxicity (96-h LC50 for fish in freshwater) ≤ 100 mg/L
Persistence and bioaccumulation criteria are used as defaults to drop the threshold, where applicable

Before a chemical is put through the REF, it must meet the following pre-screening criteria:

If the chemical is not in commerce in Canada, or if it is covered by another act of Parliament, or if it has no realistic emergency pathways, then the chemical is not recommended for addition to the Environmental Emergency Regulations (E2 regulations).

Descriptions of the REF criteria

1. Physical hazard ratings (Part 1 Substances)

Flammable gases and volatile flammable mixtures are included in Part 1 of Schedule 1 of the E2 Regulations based on their flash point and boiling point, also known as the flammability criteria used by the Transportation of Dangerous Goods RegulationsFootnote 8. Most flammable substances fulfilling these criteria will rapidly or completely vaporize at atmospheric pressure and normal ambient temperature or are easily dispersed in air and will burn readily.

Vapour cloud explosion

The volatility of a substance is taken into account by the flash point and boiling point criteria. “Flash point” is defined as the lowest temperature at which a substance gives off sufficient vapour to form an ignitable mixture with air near its surface or within a vessel.

If the chemical has a flash point less than 23°C and a boiling point less than 35°C, then the substance is capable of causing a vapour cloud explosion. If the substance does not have a flash point, or if the substance sublimes, or decomposes below the cut-off temperatures, then the substance will not be considered flammable or combustible.

According to J.P. Lacoursière (2002), the threshold quantity for a vapour cloud explosion is set at 4.5 t (10 000 lbs) because, in the event of an explosion, this quantity would result in an approximate overpressure of 3nbsp;pounds per square inch (psi) at a distance of 100 m. The calculation is performed using the TNT model with Process Hazard Analysis Software Tools (PHAST) software.


This category represents substances that have a flash point of less than 23°C or a boiling point of less than 35°C. The equation below calculates the quantity of substance necessary to evaporate 4.5 t within 10 minutes at ambient temperature (25°C) and 1.5 m/s wind speed.  The quantity necessary to create the evaporation rate is pooled into an area with a dike 50 cm in height.

The evaporation rate was determined by the following release equation (U.S. Environmental Protection Agency [EPA] 1999):


where: QR = evaporation rate (kg/min)
U = wind speed (m/s))
MW = molecular weight)
A = surface area of pool formed by the entire quantity of substance (m2))
VP = vapour pressure (mmHg))
T = temperature (Kelvin (K); temperature in °C plus 273)

Schedule 1, Part 1 substances that have thresholds above 4.5 t are combustible substances, with a few exceptions.


The current Table 2 below was slightly modified from the original data provided from the Defined Degrees of Instability Hazards of the NFPA (2002). Table 2 shows the criteria for reactivity; however, other factors may come into play such as the potential to cause a boiling liquid expanding vapour explosion (BLEVE) and accidental death histories. Table 2 below is used as a guide for expert opinion.

Table 2: reactivity

Hazard description

E2 trigger

Materials, which in themselves are readily capable of detonation or of explosive decomposition or explosive reaction at normal temperatures and pressures. This degree should include materials that are sensitive to mechanical or localized thermal shock at normal temperatures and pressures.

E2 plan trigger

Materials that in themselves are capable of detonation or of explosive reaction but that require a strong initiating source or that must be heated under confinement before initiation. This degree should include materials that are sensitive to thermal or mechanical shock at elevated temperatures and pressures or that react explosively with water without requiring heat or confinement.

Materials that in themselves are normally unstable and readily undergo violent chemical change but do not detonate. This degree should include materials that can undergo chemical change with rapid release of energy at normal temperatures and pressures or that can undergo violent chemical change at elevated temperatures and pressures. It should also include those materials that may react violently with water or that may form potentially explosive mixtures with water.

Materials that in themselves are normally stable, but that can become unstable at elevated temperatures and pressures or that may react with water with some release of energy but not violently.

Materials that in themselves are normally stable, even under fire exposure conditions, and that are not reactive with water.

(NFPA 2002)

2. Human Hazard Ratings (Part 2 Substances)

Substances that are considered hazardous when inhaled are included in Part 2 of Schedule 1 of the E2 regulations based on their toxicity, physical state, vapour pressure and accident history.

Inhalation Toxicity

The methodology used by CRAIM (2002) when setting inhalation threshold quantities is the same as that used by the U.S. EPA when developing its RMP lists. This methodology takes into consideration the potential of toxic substances to become airborne and disperse, as well as their inhalation thresholds. The REF specifies that a chemical must have a vapour pressure greater than or equal to 10 mmHg (1.33 kPa) before it can be considered for the inhalation toxicity criteria. If a substance has a vapour pressure less than 10 mmHg (1.33 kPa), inhalation toxicity will not apply.

An index of toxicity is used to analyze the inhalation threshold. This index is derived using the physical state and volatility of a substance. By order of precedent as shown in the rationale document (J.P. Lacoursière Inc., 2002), the index of toxicity is associated with the following parameters, with the final AEGL-02 values added as the highest priority. The example shown below is with IDLH.

  1. Final AEGL-02 (30 min) - data is for humans
  2. IDLH (30 min) - data is for humans
  3. ERPG (1 h) - data is for humans
  4. Mammalian data is extrapolated back to the IDLH - data is for humans
    • LC50 × 0.1 = estimated IDLH (rat 4 h - preference)
    • LC50 × 0.1 = estimated IDLH (rat 4 h - preference)
    • LD50 × 0.01 = estimated IDLH (rat - preference)
    • LDLo × 0.1 = estimated IDLH (rat - preference)



Where: MW = molecular weight
T = boiling point in °C
IDLH = immediately dangerous to life and health (g/m3)

The acute exposure guideline level (final AEGL-02 at 30 min) is the priority level for toxicity rating for humans. AEGL is the airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape (U.S. EPA, 2008).

The secondary toxicity value used is the immediately dangerous to life and health (IDLH) concentration developed by the National Institute of Occupational Safety and Health (NIOSH, 1994).  The IDLH is defined as the maximum airborne concentration from which one could escape within 30 minutes without any escape-impairing symptoms or any irreversible health effects.  If no IDLH is found, the Emergency Response Planning Guidelines (ERPG) -2 (AIHA, 2011) developed for Transport Canada will be used as an equivalent to the IDLH.

The values for the Index of toxicity are then correlated to the threshold quantities as shown in Table 3. The threshold quantities are based on amounts ranging from those found in a drum (≈ 0.22 t) to a tanker truck (9.1 t).

Table 3: Index of toxicity with respective threshold quantities
Index of toxicity with respective threshold quantities Threshold quantities metric tonnes (lbs)
< 0.01 0.22 (500)
0.01 ≤ to < 0.05 0.45 (1000)
0.05 ≤ to < 0.1 1.13 (2500)
0.1 ≤ to < 0.3 2.27 (5000)
0.3 ≤ to < 1 4.50 (10 000)
1 ≤ to < 10 6.80 (15 000)
≥ 10 9.10 (20 000)

(J.P. Lacoursière Inc., 2002)


Previously, it was concluded that 10 years was sufficient time for a carcinogenic substance to cause cancer in humans. Due to new evidence, the exposure time for a substance to cause cancer has been lowered to 5 years in accordance with the precautionary principle. It has been shown that an infant is 10 times more at risk than an adult (U.S. EPA, 2005).

The REF uses 2 sets of carcinogenicity ratings established by the International Agency for Research on Cancer (IARC, 1999) and the U.S. EPA (U.S. EPA, 2002) as shown in tables 4 and table5. The IARC or U.S. EPA classifications will only trigger an E2 plan if the substance is persistent in the environment for at least 5 years, or the substance is classified as indefinitely persistent. If these criteria are met, the substance is then assigned a threshold of 0.22 t. If the two classification systems disagree on a chemical’s rating, the most conservative assessment is used, and the chemical is rated accordingly.

Table 4: IARC human and animal carcinogenicity classifications


E2 trigger

Group 1:

  • The agent (mixture) is carcinogenic to humans
  • Sufficient evidence of carcinogenicity in experimental animals

E2 plan trigger

Group 2A:

  • The agent (mixture) is probably carcinogenic to humans

E2 plan trigger

Group 2B:

  • The agent (mixture) is possibly carcinogenic to humans
  • Less than sufficient evidence of carcinogenicity in experimental animals

E2 plan trigger

Group 3:

  • The agent (mixture or exposure circumstance) is not classifiable as to its carcinogenicity to humans
  • Evidence of carcinogenicity is inadequate or limited in experimental animals

Group 4:

  • The agent (mixture) is probably not carcinogenic to humans
  • Evidence suggesting lack of carcinogenicity in experimental animals

(IARC, 1999)

Table 5: U.S. EPA carcinogenicity classifications


E2 trigger

Carcinogenic to humans (A)
Compelling evidence of carcinogenicity in animals.

E2 plan trigger

Likely to be carcinogenic to humans (B1)
Strong experimental evidence of carcinogenicity in animals.

E2 plan trigger

Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential (B2)
Evidence from animal data is suggestive of carcinogenicity, but is judged not sufficient for a conclusion, for example, marginal increase in tumours, evidence only in a single study, evidence is limited to tumours in one sex of one species. Further studies would be needed.

E2 plan trigger

Data are inadequate for an assessment of human carcinogenic potential (C)
Data are judged inadequate to perform an assessment. This includes lack of pertinent or useful data; evidence is conflicting.

Not likely to be carcinogenic to humans (D)
Animal evidence that demonstrates lack of carcinogenic effect in at least two well-designed and well-conducted studies in two appropriate animal species.

(U.S. EPA, 1986 and 1999, modified)

3. Environmental hazard ratings (Part 3 Substances)

Part 3 of Schedule 1, referred to as other hazardous substances, is a new addition to the list of substances covered by the Environmental Emergency Regulations. Substances in Part 3 can be characterized as being persistent, bioaccumulative, carcinogenic to humans or toxic to aquatic organisms.

The Toxic Substances Management Policy (TSMP) of CEPA uses persistence, bioaccumulation and toxicity (PBT) criteria for determining when an organic chemical is to be considered for virtual elimination in Canada. The virtual elimination of a toxic substance released into the environment, as a result of human activity, requires the ultimate reduction of its releases to the lowest concentration that can be accurately measured, using routine sampling and analytical methods (Environment Canada 1995). TSMP virtual elimination criteria are shown in Table 6.

Table 6: TSMP criteria for the selection of substances for virtual elimination
Persistence (half-life) Bioaccumulation Toxicity Predominantly anthropogenic
Air ≥ 2 days BAF ≥ 5000
BCF ≥ 5000
log Kow ≥ 5.0
CEPA-toxic equivalent
Concentration in environment largely resulting from human activity
Water ≥ 182 days
Soil ≥ 182 days
Sediment ≥ 365 days

(Environment Canada, 1995)


Chemical substances that degrade slowly in the environment (that is, are relatively resistant to biodegradation, hydrolysis and photolysis processes) represent potential environmental problems. Persistence is measured as a half-life, meaning the period it takes the concentration of a substance to be reduced by half, by transformation, in a medium (Environment Canada, 2000). A compound released into the environment has a tendency to partition (that is, accumulate) into one medium (air, water, soil or sediment) more than another. Partitioning, transport and transformation rates differ in each medium.

The persistence criteria with the highest scores are based on the Persistence and Bioaccumulation Regulations (Environment Canada, 2000). These are the standards set by CEPA for substances that should be virtually eliminated from the environment. Those criteria are the same as the U.S. EPA persistence, bioaccumulation and toxicity (PBT) criteria used for the Toxic Release Inventory (TRI), New Substances Evaluation and other EPA programs (U.S. EPA, 1999, 1999a). These persistence criteria can be seen in Table 7. The rest of the scale was created by estimating half of the remaining time duration.

Inorganic substances are considered infinitely persistent in the environment since the metal ion (that is, lead, arsenic) continuously separates from the original substance and forms new compounds within the environment. This implies that the metal ion within inorganic substances does not degrade. No threshold quantity exists for persistence criteria alone; this category is combined with aquatic toxicity for persistence in water.

Table 7: persistence of organic chemicals in the environment
Air Water/Soil Sediment E2 trigger
≥ 2 daysa ≥ 182 daysa ≥ 365 daysa Virtual elimination criteriaa
E2 plan trigger
≥ 1 to < 2 daysb ≥ 60b to < 182 days ≥ 60b to < 365 days E2 plan trigger
≥ 12 h to < 1 day ≥ 30 to < 60 days ≥ 30 to < 60 days  
≥ 6 h to < 12 h ≥ 14 to < 30 days ≥ 14 to < 30 days  
< 6 h < 14 days < 14 days  

a Environment Canada, 1995.
b Or evidence of atmospheric transport to remote regions such as the Arctic (Environment Canada, 1995).

Bioaccumulation (BCF/BAF/Log Kow)

Bioaccumulation is the biological accumulation of a substance into various tissues of a living organism. Table 8 shows all three criteria can be used to determine bioaccumulation. There are different ways to estimate the bioaccumulation within an organism:

  1. “bioconcentration factor” means the ratio of the concentration of a substance in an organism to the concentration in water, based only on uptake from the surrounding medium (Environment Canada, 2000);
  2. “octanol-water partition coefficient” means the ratio of the concentration of a substance in an octanol phase to the concentration of the substance in the water phase of an octanol-water mixture (Environment Canada, 2000);
  3. “bioaccumulation factor” means the ratio of the concentration of a substance in an organism to the concentration in water, based on uptake from the surrounding medium and food (Environment Canada, 2000).

Table 6 shows the bioaccumulation criteria used in the REF. Both the highest values for the BCF/BAF and the log Kow are consistent with the CEPA virtual elimination clause (Environment Canada, 2000). The OECD criteria for BCF is ≥ 500, or if BCF /BAF is absent, one uses the log Kow ≥ 4 (OECD, 2001). No threshold quantity exists within the REF for bioaccumulation alone; this category is combined with aquatic toxicity.

Table 8: bioaccumulation of organic chemicals in the environment
BCF/BAF Log Kow E2 trigger
≥ 5000c ≥ 5c Virtual elimination criteriac;
E2 plan trigger
≥ 500 to < 5000 ≥ 4 to < 5
(unless BCF < 500)
E2 plan trigger
≥ 50 to < 500 ≥ 3 to < 4 Sediment
0 to < 50 ≥ 2 to < 3 Sediment
-- < 2 Sediment

c (Environment Canada, 1995) (OECD 2001, modified)

Aquatic toxicity

Freshwater species toxicity data for fish in Canadian waters are collected for the REF. Acute toxicity is determined using a freshwater fish 96-h LC50. The most sensitive value (lowest value) for a freshwater fish is selected and a robust study is conducted for quality control measures to determine the quality of the laboratory experiment. If the value fails the robust study, then the next most sensitive species is selected. Ground water, drainages, tributaries and rivers can all lead to contamination of a water body. Aquatic toxicity uses the persistence and bioaccumulation criteria to assist in determining the threshold quantity.

Table 9: acute aquatic toxicity thresholds
Criteria Extremely toxic Highly toxic Moderately toxic Slightly toxic
Persistence (P) (water) P ≥ 6 months 2 months ≤ P < 6 months Not applicable (N/A) N/A
Bioaccumulation (BCF)
Log Kow (Kow)
BCF ≥ 5000
log Kow ≥ 5
500 ≤ BCF < 5000
4 ≤ Kow < 5
(unless BCF < 500)
Acute aquatic toxicity (AAT) (96 h LC50 - mg/L) 0.1 ≤ AAT 0.1 < AAT  ≤ 1 1 < AAT ≤ 10 10 < AAT ≤ 100
Threshold quantity tonnes (lbs) 0.22 (500 lbs) 1.13 (2500 lbs) 4.50 (10 000 lbs) 9.10 (20 000 lbs)

How to use Table 9

If the substance falls within the range 0.1 mg/L ≤ fish LC50 value ≤ 100 mg/L, then the substance is recommended for addition under Schedule 1, Part 3 of the Environmental Emergency Regulations, after the quality control robust study has been completed.  Furthermore, if the substance meets the categories of persistence or bioaccumulation criteria set out in Table 9, then the threshold defaults to that level. For sample calculations, see Table 10.

Table 10: example calculations for aquatic toxicity
Value of LC50(mg/L) Persistence data Bioaccumulation data Final threshold (tonnes)
P ≥ 6 months 500 ≤ BCF < 5000 No threshold
8e 2 months ≤ P < 6 months No data 1.13
0.01f 4 ≤ Kow < 5 2 months ≤ P < 6 months 0.22
50g No data 500 ≤ BCF < 5000 1.13

e Value of LC50 is over 100 mg/l - considered practically non-toxic.
f Threshold is 4.50 t, but persistence criteria drops threshold to 1.13 t.
g Threshold is 0.22 t and persistence and bioaccumulation criteria are higher than 0.22 t, therefore take the lowest threshold.
h Threshold is 9.10 t, but bioaccumulation data drops the threshold to 1.13 t.

Robust studies

The reliability of a data point is crucial for the evaluation. For this reason, aquatic toxicity, bioaccumulation and persistence data points are analyzed using a robust study summary created by the OECD. A robust study summary is a series of questions based on information provided in a scientific journal. Thus, for each data point selected as the most sensitive endpoint found in a book or database, the original journal is examined via a robust study summary. Each scientific journal is assigned a Klimisch rating from 1 to 4, where 1 and 2 indicate journals that are experimentally reliable, whereas 3 and 4 are scores indicative of an unacceptable data point.

Standard references that are peer-reviewed such as The Merck Index, The Condensed Chemical Dictionary, The CRC Handbook of Chemistry and Physics, the Beilstein Database, and international reviews like Concise International Chemical Assessment Documents (CICADS) and Environment Health Criteria documents should be used as much as possible for data sources.

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