Rationale for list of regulated substances under Canadian Environmental Protection Act: chapter 4

4. Threshold Methodologies

It is important to have a sound and transparent methodology for assignment of threshold quantities for hazardous substances. The methodology should include an explanation of the basis for establishing the list and account for specific factors in setting the threshold quantities. Moreover, a sound methodology is essential for making changes to the list of substances and their threshold quantities to keep the regulation current.

The methodology should follow the principle of "Equivalence of Harm" i.e. the threshold quantities of hazardous substance in each category (toxic, flammable, etc) should be such to cause the same degree of harm.

The proposed methodology is the one that EPA used for setting up the RMP lists.

Suggestions were made that site-specific factors should be considered in setting or modifying thresholds, such as population density, ecosystems sensitivity, safety devices, experience, uses of the substance, and handling conditions. EPA recognized that these and many other site-specific factors could affect the likelihood of occurrence or the effects of a release. Accounting for these factors has the advantage of more specifically tailoring threshold quantities based on common use patterns of the substances and of the particular site in which they would be used. One serious disadvantage of applying site-specific factors to setting thresholds would be that such an approach would be inappropriate for ubiquitous chemicals, such as chlorine and ammonia, because of the innumerable applications that would have to be considered. A greater disadvantage to this approach is that the intrinsic hazard of a chemical will still be present even when it is used outside of a "typical" scenario. It is therefore not feasible to develop a methodology for establishing threshold quantities based on site-specific factors that would be applicable nationwide. However, for the threshold determination at a specific site, substance-specific factors and use scenarios can be considered in determining whether there is a threshold quantity on-site.

The RMP Methodology for choosing threshold quantities follows.

4.1. Threshold Methodology for Toxic Substances

For the setting of threshold quantities for Toxic Substances under the RMP, EPA used the methodology for the development of threshold planning quantities (TPQs) developed for extremely hazardous substances (EHSs) listed under EPCRA (SARA Title III) section 302. This methodology takes into account the potential of toxic substances to become airborne, their dispersion potential, and toxicological properties, with adjustment based on chemical reactivity and other factors.

The Immediately Dangerous to Life and Health (IDLH) level developed by the National Institute of Occupational Safety and Health (NIOSH), or an approximation of the IDLH based on animal toxicity data, was used as an index of toxicity. 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. IDLHs presented in the 1990 edition of the NIOSH Pocket Guide to Chemical Hazards were used where available.

Physical state and volatility were used to derive an index of the chemical's potential to become airborne and disperse. The two indices were combined to produce an overall risk "ranking factor" defined as IDLH/V, where V is the index of potential to become airborne and disperse. Threshold quantities were assigned to groups of substances according to their relative importance. See Exhibit 1 and Appendix B for Ranking of chemicals.

For substances without a published IDLH, mammalian toxicity data were used to derive a value equivalent to the IDLH as follows:, in order of preferred toxicity data:

  • Estimated IDLH = LC50 x 0.1
  • Estimated IDLH = LCLO
  • Estimated IDLH = LD50 x 0.01
  • Estimated IDLH = LDLO x 0.1


  • LC50 is the median lethal concentration, the concentration of the chemical in air at which 50 percent of the test animals died;
  • LCLO is the lowest concentration in air at which any test animals died;
  • LD50 is the median lethal dose, the dose that killed 50 percent of the test animals; and
  • LDLO is the lowest dose at which any test animals died.

Revised or updated toxicology data were used, based on the December 1990, Registry of Toxic Effects of Chemical Substances (RTECS).

EPA chose to use IDLH or its equivalent rather than the Emergency Response Planning Guideline level 3 (ERPG-3) or the Emergency Response Planning Guideline level 2 (ERPG-2) from the American Industrial Hygiene Association (AIHA) or some other measure of toxic concentrations because there are many more published IDLH values available than ERPG values; in addition a method is available for deriving an IDLH equivalent from toxicity data.

The Emergency Response Planning Guideline (ERPG) values are intended to provide estimates of concentration ranges above which one could reasonably anticipate observing some adverse effects as described in the definition of ERPG-3, ERPG2 and ERPG-1 as a consequence of exposure to a specific substanceFootnote 10  :

  • The ERPG-3 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects.
  • The ERPG-2 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair their abilities to take protective action.
  • The ERPG-1 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined objectionable odour.

For the following chemicals, the following "Toxicity" criteria were used because of lack of IDLH 1990 or reliable toxicity data:

  • ERPG-2 (1991) Chlorosulfonic acid
  • ERPG-2 (2002) 1,2-Dichloroethane
  • IDLH (1994) Hydrobromic acid
  • IDLH (1994) Ketene
  • IDLH (1997) Trioxychlorofluoride
  • LC50 Thionyl chloride
  • LCLO Cyanogen bromide

The index of potential to become airborne and disperse (V) was derived based on physical state and volatility. For substances that are gases under ambient conditions, V was assumed to have a value of 1, indicating that in an accidental release, the total quantity of chemical involved in the release could become airborne. For liquids, V was calculated by estimating the rate of volatilization from a pool (assumed to be one centimetre in depth) on a flat non-absorbing surface using equations presented in Appendix B. Liquids were assumed to be at their boiling point, and all liquids were assumed to have the same density as water. A transfer coefficient was estimated by reference to water. Because of these assumptions, the only variables used in the calculation of V were the molecular weight and boiling point of the liquid. Taking into account these assumptions, the equation used to derive V is as follows (see Appendix B for additional details):

V = (1.6 x MW 0.67) / (T + 273)


  • MW is the molecular weight, and
  • T is the boiling temperature in degrees Celsius.

The toxic substances were ranked according to the ranking factor IDLH/V and assigned threshold quantities of 0.22 t (500 lbs), 0.45 t (1,000 lbs), 1.13 t (2,500 lbs), 2.27 t (5,000 lbs), 6.80 t (15,000 lbs) or 9.10 t (20,000 lbs) based on order of magnitude ranges in the ranking factors. The threshold quantities selected are, at the minimum level of 0.22 t (500 lbs), representative of drum-size containers, and, at the maximum of 9.10 t (20,000 lbs). The range of threshold quantities reflect the relative hazards among the listed toxics; the upper limit of 9.10 t (20,000 lbs) represents typical handling quantities, and would still be protective of the public for those substances which would have the higher thresholds.

Several toxic substances also meet the flammability criteria, and thus could be assigned two thresholds. Toxic substances that also meet the criteria for listing as flammable substances are assigned the lower of the thresholds. For example methyl chloride which meets the criteria for listing of flammability and, therefore, is assigned the threshold quantity of 10,000 pounds rather than the 20,000 pounds that would apply under the methodology for toxics. The threshold quantities assigned based on the ranking factors were reviewed, and changes were made based on other toxicity data, rapid absorption, chemical reactivity, and consideration of specific handling, formulation, and use information.

Table 8 - Threshold Values Index
Index Threshold Quantities Tonnes (lbs)
Note : * Numbers rounded to the second digit
<0.01 0.22* (500)
0.01 to <0.05 0.45* (1,000)
0.05 to <0.1 1.13* (2,500)
0.1 to <0.3 2.27* (5,000)
0.3 to <1 4.50* (10,000)
1 to <10 6.80* (15,000)
≥ 10 9.10* (20,000)

4.2. Threshold Quantities for Flammable Substances

EPA's analysis of the hazards of flammable chemicals indicates that the greatest hazard to the public from these substances is from vapour cloud explosions. Heat radiation from pool fires, vapour cloud fires, or fireball resulting from boiling liquid expanding vapour cloud explosions (BLEVEs) can also be a threat to the public. However, EPA's analysis indicates that for a given quantity of a flammable chemical, vapour cloud explosions pose the greatest threat over the greatest distance. Historical data indicate that vapour cloud explosions are unlikely for vapour cloud containing quantities less than 4 545 kg (10,000 lbs). The quantity in a vapour cloud resulting from an accidental release of a flammable gas or volatile flammable liquid could vary greatly depending on site-specific and accident-specific conditions, as well as properties of the chemical released.

EPA has a list of 62 flammable gases and volatile flammable liquids under the RMP. Because it would be difficult to set chemical-specific thresholds based on all the factors that might affect a release, EPA has chosen to set the threshold for all the listed flammable substances at 4,545 kg, based on the potential for vapour cloud explosions. EPA's analysis indicates that the detonation of 4,545 kg of a flammable vapour (e.g., ethylene, propane, propylene, etc.) could have a potentially lethal effect on people at a distance of 100 metres from the site of the detonation.

EPA believes that this threshold is conservative and protective because the vapour cloud resulting from a release of 4,545 kg would probably contain a quantity less than 4,545 kg, even though all the listed flammable substances are gases or volatile liquids. Establishing one threshold for all the flammable substances on the list also simplifies the regulatory process. The 4,545 kg is consistent with the OSHA's threshold for flammable substances in its Process Safety Management Standard. See Exhibit 2.

Substances that are listed under RMP for toxicity may also meet the criteria for listing for flammability. For these substances, the thresholds have been set based on toxicity, as described above. The substances are included on the list of toxic substances only. Toxic substances proposed for listing that meet the criteria for flammability are listed in Exhibit 3. For 11 of these substances, the TQ assigned on the basis of toxicity is lower than the 4,545 kg threshold that would be assigned on the basis of flammability. For the remaining four, the threshold would be 4,545 kg for either toxicity or flammability.

4.3. Threshold Methodology for Explosives

The detonation of high explosives produces violent shock waves. EPA's analysis of explosives indicates that blast wave overpressure of 3.0 psi could have potentially lethal effects on people from the indirect effects of an explosion. This overpressure level could cause serious structural damages to buildings (which could lead to serious or fatal injuries to people), lead to serious wounds from flying glass, and potentially cause eardrum rupture. In addition, an overpressure of this level could hurl a person to the ground or against other objects, potentially causing injury. The indirect effects of a blast overpressure of 3.0 psi would probably not be lethal. Lower overpressure levels also could potentially lead to serious or fatal injuries from indirect effects such as injury from flying glass or other debris in some cases. However, for lower pressures, the likelihood of a fatality is lower because there would be less damage to buildings and flying objects would have less force. EPA decided that for the purposes of the RMP, 3.0 psi was a reasonable overpressure level to consider.

To determine a threshold for explosives, EPA used the scaling law of distances, which relates quantity of explosive material and distance for a given overpressure, to estimate the quantity of high explosives that would produce an overpressure of 3.0 psi at a distance of 100 metres in the event of a detonation. The scaling law is represented by the following equation:

D = K x W1/3


  • D = Required, or potentially affected distance, feet.
  • K = Protection factor depending upon the degree of risk assumed or permitted, empirically derived based on effects of overpressure.
  • W = TNT equivalent weight, pounds; i.e., the weight of trinitrotoluene (TNT) that would yield the same peak overpressure or impulse at a given distance as the total weight of explosive material under consideration.

Exhibit 4 shows the distances to various overpressure levels from explosion of several quantities of high explosives, based on the scaling law, assuming the high explosive is equivalent to TNT in explosive power.

Based on calculations using the scaling law, EPA decided to set the threshold for high explosives at 2.27 t (5,000 lbs), the quantity that would lead to an overpressure of about 3 psi at a distance of 100 metres in the event of an explosion. Individual explosives may vary in their explosive capacity.

It should be noted that, for the purposes of the Section 200 regulation, explosives have been specifically excluded from consideration. This is due to the fact that they are regulated by Natural Resources Canada under the Explosives Act where the environmental emergency planning aspects are adequately addressed.

4.4. Limitations of threshold quantities

Methods for setting threshold quantities for substances in each category were taken from the U.S. Environmental Protection Agency (EPA).

EPA does not consider these threshold quantities to be a precise measure of a "safe" level; no such level can be determined. The risk posed by any chemical release depends on the particular circumstances at the time of the release.

For example, releases of the same quantity of the chemical may pose very different threats depending on the location of a facility, weather at the time of the release, the elevation of the source of the release (e.g., a release from a smokestack versus a ground level release), and the pressure and temperature at the time of the substance, among other factors.

4.5. Other threshold quantity options considered

In addition to the proposed methodology for setting thresholds for toxic substances, three alternative options were considered.

4.5.1. Dispersion modeling

One option uses the vapour quantity method, based on air dispersion modeling, to determine the quantity in air needed to equal the "Immediately Dangerous to Life and Health (IDLH), (published by the National Institute for Occupational Safety and Health) concentration level at 100 metres from the point of release. To derive threshold quantities, a concentration level equal to the IDLH or its equivalent was assumed to be reached at a distance of 100 metres from the source of the release. The U.S. EPA calculated a release rate that would produce that concentration level at 100 m, by using air dispersion modelling techniques. The dispersion modeling used was based on equations presented in Technical Guidance for Hazards Analysis (EPA, Federal Emergency Management Agency (FEMA), and Department of Transport (DOT), 1987). For the calculations, moderate conditions of a wind speed of 4.3 metres per second (10 miles per hour), atmospheric stability D, and urban conditions were assumed. The duration of the release was assumed to be 30 minutes (because the IDLH is based on a 30-minute exposure), and a quantity was calculated by multiplying the release rate by the duration. For comparison, the same calculations were carried out assuming extreme conditions of wind speed 1.5 metres per second stability F, and open, rural conditions.

The assumptions made for modeling had a great effect on the results obtained. The quantity calculated assuming moderate conditions is approximately 100 times less than that calculated assuming extreme conditions. Varying the assumptions could lead to many different calculated quantities. The quantity calculated is directly proportional to the wind speed, the dispersion coefficients, the toxic concentration, and the duration of the release.

It was felt that such an approach would be difficult to implement on a national basis. The conditions at the time of an actual release could vary greatly; therefore, the results of chemical-specific calculations such as those carried out using this methodology may have little relation to what might happen during an actual release.

4.5.2. Seveso II Directive

Here are extracts of the Seveso Directive (Seveso) for some specific obligations for operators and the lists of dangerous substances and their threshold quantitiesFootnote 11 .

Article 6


  1. Member States shall require the operator to send the competent authority a notification within the following time-limits:
    • for new establishments, a reasonable period of time prior to the start of construction or operation,
    • for existing establishments, one year from the date laid down in Article 24 (1).
  2. The notification required by paragraph 1 shall contain the following details:

    1. the name or trade name of the operator and the full address of the establishment concerned;
    2. the registered place of business of the operator, with the full address;
    3. the name or position of the person in charge of the establishment, if different from (a);
    4. information sufficient to identify the dangerous substances or category of substances involved;
    5. the quantity and physical form of the dangerous substances or substances involved;
    6. the activity or proposed activity of the installation or storage facility;
    7. the immediate environment of the establishment (elements liable to cause a major accident or to aggravate the consequences thereof).
  3. In the case of existing establishments for which the operator has already provided all the information under paragraph 2 to the competent authority under the requirements of national law at the date of entry into force of the Directive, notification under paragraph 1 is not required.
  4. In the event of:

    • any significant increase in the quantity or significant change in the nature or physical form of the dangerous substance present, as indicated in the notification provided by the operator pursuant to paragraph 2, or any change in the processes employing it, or
    • permanent closure of the installation.
Article 7

Major-accident prevention policy

  1. Member States shall require the operator to draw up a document setting out his major-accident prevention policy and to ensure that it is properly implemented. The major-accident prevention policy established by the operator shall be designed to guarantee a high level of protection for men and the environment by appropriate means, structures and management systems.
  2. The document must take account of the principles contained in Annex III (Of the Seveso directive) and be made available to the competent authorities for the purposes of, amongst other things, implementation of Articles 5 (2) and 18.
  3. This article shall not apply to the establishments referred to in article 9.
Article 9

Safety report

  1. Member States shall require the operator to produce a safety report for the purposes of:

    1. demonstrating that a major-accident prevention policy and a safety management system for implementing it have been put into effect in accordance with the information set out in Annex III (of the Seveso Directive);
    2. demonstrating that major-accident hazards have been identified and that the necessary measures have been taken to prevent such accidents and to limit their consequences for man and the environment;
    3. demonstrating that adequate safety and reliability have been incorporated into the design, construction, operation and maintenance of any installation, storage facility, equipment infrastructure connected with its operation which are linked to major-accident hazards inside the establishment;
    4. demonstrating that internal emergency plans have been drawn up and supplying information to enable the external plan to be drawn up in order to take the necessary measures in the event of a major accident;
    5. providing sufficient information to the competent authorities to enable decisions to be made in terms of the siting of new activities or developments around existing establishments.
  2. The safety report shall contain at least the data and information listed in Annex II (of the Seveso Directive). It shall also contain an updated inventory of the dangerous substances present in the establishment.

    Safety reports, or parts of reports, or any other equivalent reports produced in response to other legislation, may be combined to form a single safety report for the purposes of this Article, where such a format obviates the unnecessary duplication of information and the repetition of work by the operator or competent authority, on condition that all the requirements of this Article are complied with.
  3. The safety report provided for in paragraph 1 shall be sent to the competent authority within the following time limits:
    • for new establishments, a reasonable period of time prior to the start of construction or of operation,
    • for existing establishments not previously covered by Directive 82/501/EEC, three years from the date laid down in Article 24 (1)
    • for other establishments, two years from the date laid down in Article 24 (1),
    • in the case of the periodic reviews provided for in paragraph 5, without delay.
  4. Before the operator commences construction or operation, or in the case referred to in the second, third and fourth indents of paragraph 3, the competent authority shall within a reasonable period of receipt of the report:
    • communicate the conclusions of its examination of the safety report to the operator, if necessary after requesting further information, or
    • prohibit the bringing into use, or the continued use, of the establishment concerned, in accordance with the powers and procedures laid down in Article 17.
  5. The safety report shall be periodically reviewed and when necessary updated:
    • At least every five years,
    • At any other time at the initiative of the operator or the request of the competent authority, where justified by new facts or to take account of new technical knowledge about safety matters, for example arising from analysis of accidents or, as far as possible "near misses", and of developments in knowledge concerning the assessment of hazards.
    1. Where it is demonstrated to the satisfaction of the competent authority that particular substances present at the establishment, or any part thereof, are in a state incapable of creating a major-accident hazard, then the Member State may, in accordance with the criteria referred to in subparagraph (b), limit the information required in safety reports to those matters which are relevant to the prevention of residual major-accident hazards and the limitation of their consequences for man and the environment.
    2. Before this directive is brought into application, the Commission, acting in accordance with the procedure laid down in Article 16 of Directive 82/501/EEC, shall establish harmonized criteria for the decision by the competent authority that an establishment is in a state incapable of creating a major accident hazard within the meaning of subparagraph (a). Subparagraph (a) shall not be applicable until those criteria have been established.
    3. Member States shall ensure that the competent authority communicates a list of the establishments concerned to the Commission, giving reasons. The Commission shall forward the list annually to the Committee referred to in Article 22.

It should be noted that for Part II of the Directive, the European Union used categories of substances and preparations instead of naming specifically the substances.

The choice of threshold quantities was the result of negotiations between Competent Authorities.

  1. Mixtures and preparations are treated in the same way as pure substances provided they remain within concentration limits set according to their properties under the relevant Directives given in Part 2, Note 1, or their latest adaptation to technical progress, unless a percentage composition or other description is specifically given.
  2. The qualifying quantities set out below relate to each establishment.
  3. The quantities to be considered for the application of the relevant Articles are the maximum quantities that are present or are likely to be present at any one time. If dangerous substances present within an establishment are found in quantities equal to or less than 2 % of the relevant qualifying quantity, and if their location is such that it cannot act as an initiator of a major accident elsewhere on the site, they shall be ignored when calculating total quantity present on site.
  4. The rules given in Part 2, Note 4 governing the addition of dangerous substances, or categories of dangerous substances, apply where appropriate.
Part 1 - Named substances
Where a substance or group of substances listed in Part 1 also falls within a category of Part 2, the qualifying quantities set out in Part 1 must be used.
Dangerous substances Qualifying quantity (tonnes) for the application of
Articles 6 and 7 Article 9
Ammonium nitrate1 350 2500
Ammonium nitrate2 1250 5000
Arsenic pentoxide, arsenic (V) acid and/or salts 1 2
Arsenic trioxide, arsenious (III) acid and/or salts - 0.1
Bromine 20 100
Chlorine 10 25
Nickel compounds in inhalable powder form (nickel monoxide, nickel dioxide, nickel sulphide, trinickel disulphide, dinickel trioxide - 1
Ethyleneimine 10 20
Fluorine 10 20
Formaldehyde (concentration ( 90 %) 5 50
Hydrogen 5 50
Hydrogen chloride (liquefied gas) 25 250
Lead alkyls 5 50
Liquefied extremely flammable gases (including LPG) and natural gas 50 200
Acetylene 5 50
Ethylene oxide 5 50
Propylene oxide 5 50
Methanol 500 5000
4,4-Methylenebis(2-chloraniline) and/or salts, in powder form - 0.01
Methyl isocyanate - 0.15
Oxygen 200 2000
Toluene diisocyanate 10 100
Carbonyl dichloride (phosgene) 0.3 0.75
Arsenic trihydride (arsine) 0.2 1
Phosphorus trihydride (phosphine) 0.2 1
Sulphur dichloride 1 1
Sulphur trioxide 15 75
Polychlorodibenzofurans and polychlorodibenzodioxins (including TCDD), calculated in TCDD equivalent - 0.001
The following CARCINOGENS:
4-Aminobiphenyl and/or its salts, Benzidine and/or salts, Bis(chloromethyl) ether, Chloromethyl methyl ether, Dimethylcarbamoyl chloride, Dimethylnitrosamine, Hexamethylphosphoric triamide, 2-Naphtylamine and/or salts, and 1,3-Propanesultone 4-nitrodiphenyl
0.001 0.001
Automotive petrol and other petroleum spirits 5000 50000
  • 1 Ammonium nitrate (350 / 2500)
    This applies to ammonium nitrate and ammonium nitrate compounds in which the nitrogen content as a result of the ammonium nitrate is more than 28 % by weight (compounds other than those referred to in Note 2) and to aqueous ammonium nitrate solutions in which the concentration of ammonium nitrate is more than 90 % by weight.
  • 2 Ammonium nitrate (1250/5000)
    This applies to simple ammonium-nitrate based fertilizers which comply with Directive 80/876/EEC and to composite fertilizers in which the nitrogen content as a result of the ammonium nitrate is more than 28 % in weight (a composite fertilizer contains ammonium nitrate with phosphate and/or potash).

Part 2
Categories of substances and preparations not specifically named in Part 1
  Qualifying quantity (tonnes) of dangerous substances as delivered in Article 3 (4), for the application of
Articles 6 and 7 Article 9
1. Very Toxix 5 20
2. Toxic 50 200
3. Oxidizing 50 200
4. Explosive (where the substance or preparation falls within the definition given in Note 2 (a)) 50 200
5. Explosive (where the substance or preparation falls within the definition given in Note 2 (b)) 10 50
6. Flammable (where the substance or preparation falls within the definition given in Note 3 (a)) 5000 50000
7 a. Highly Flammable (where the substance or preparation falls within the definition given in Note 3 (b) (1)) 50 200
7 b. Highly Flammable liquids (where the substance or preparation falls within the definition given in Note 3 (b) (2)) 5000 50000
8. Extremely Flammable (where the substance or preparation falls within the definition given in Note 3 (c)) 10 50
9. Dangerous for the Environment in combination with risk phrases: - -
9(i) R50: 'Very toxic to aquatic organisms' 200 500
9(ii) R51: 'Toxic to aquatic organisms'; and R53: 'May cause long term adverse effects in the aquatic environment' 500 2000
10. Any Classification not covered by those given above in combination with risk phrases: - -
10(i) R14: 'Reacts violently with water' (including R14/15) 100 500
10(ii) R29: 'in contact with water, liberates toxic gas' 50 200


  1. Substances and preparations are classified according to the following Directives (as amended) and their current adaptation to technical progress.

    • Council Directive 67/548/EEC of 27 June 1967 on the approximation of the laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substancesFootnote 12 ,
    • Council Directive 88/379/EEC of 7 June 1988 on the approximation of the laws, regulations and administrative provisions of the Member States relating to the classification, packaging and labelling of dangerous preparationsFootnote 13 ,
    • Council Directive 78/631/EEC of 26 June 1978 on the approximation of the laws of the Member States relating to the classification, packaging and labelling of dangerous preparations (pesticides)Footnote 14 

    In the case of substances and preparations which are not classified as dangerous according to any of the above Directives but which nevertheless are present, or are likely to be present, in an establishment and which possess or are likely to possess, under the conditions found at the establishment, equivalent properties in terms of major-accident potential, the procedures for provisional classification shall be followed according to the relevant Article of the appropriate Directive.

    In the case of substances and preparations with properties giving rise to more than one classification, for the purposes of this Directive the lowest thresholds shall apply.

    For the purposes of this Directive, a list providing information on substances and preparations shall be established, kept up to date and approved by the procedure set up under Article 22.

  2. An 'explosive' means:

    1. a substance or preparation which creates the risk of an explosion by shock, friction, fire or other sources of ignition (risk phrase R 2),
    2. a pyrotechnic substance is a substance (or mixture of substances) designated to produce heat, light, sound, gas or smoke or a combination of such effects through non-detonating self-sustained exothermic chemical reactions, or
    3. an explosive or pyrotechnic substance or preparation contained in objects;
    4. a substance or preparation which creates extreme risks of explosion by shock, friction, fire or other sources of ignition (risk phrase R 3).
  3. 'Flammable', 'highly flammable', and 'extremely flammable' in categories 6, 7 and 8 mean:

    1. flammable liquids:

      substances and preparations having a flash point equal to or greater than 21°C and less than or equal to 55°C (risk phrase R 10), supporting combustion;
    2. highly flammable liquids:

      • substances and preparations which may become hot and finally catch fire in contact with air at ambient temperature without any input of energy (risk phrase R 17),
      • substances which have a flash point lower than 55°C and which remain liquid under pressure, where particular processing conditions, such as high pressure or high temperature, may create major-accident hazards;
      • substances and preparations having a flash point lower than 21°C and which are not extremely flammable (risk phrase R 11, second indent);
    3. extremely flammable gases and liquids:

      • liquid substances and preparations which have a flash point lower than 0°C and the boiling point (or, in the case of a boiling range, the initial boiling point) of which at normal pressure is less than or equal to 35°C (risk phrase R 12, first indent), and
      • gaseous substances and preparations which are flammable in contact with air at ambient temperature and pressure (risk phrase R 12, second indent), whether or not kept in the gaseous or liquid state under pressure, excluding liquefied extremely flammable gases including liquefied petroleum gases (LPG) and natural gas referred to in Part 1, and
      • liquid substances and preparations maintained at a temperature above their boiling point.
      • The addition of dangerous substances to determine the quantity present at an establishment shall be carried out according to the following rule:

        if the sum

        q1 / Q + q2 / Q + q3 / Q + q4 / Q + q5 / Q + .... 1


        • qx = the quantity of dangerous substances x (or category of dangerous substances) falling within Parts 1 or 2 of this Annex,
        • Q = the relevant threshold quantity from Parts 1 or 2,

        then the establishment is covered by the relevant requirements of this Directive.

    This rule will apply for the following circumstances:

    • for substances and preparations appearing in Part 1 at quantities less than their individual qualifying quantity present with substances having the same classification from Part 2, and the addition of substances and preparations with the same classification from Part 2;
    • for the addition of categories 1, 2 and 9 present at an establishment together;
    • for the addition of categories 3, 4, 5, 6, 7a, 7b and 8, present at an establishment together.

4.5.3. United States Occupational Safety and Health Administration

The United States Occupational Safety and Health Administration (OSHA) thresholds quantities for toxic substances listed in the Process Safety Management Standard (57 FR 6356, February 24, 1992) are based on dispersion modeling. OSHA did not specify the concentrations that were used in deriving the thresholds. Specific conditions are as follows:

  • Meteorological conditions are assumed to be the average conditions (4.3 m/s wind speed, D stability).
  • Continuous, steady-state release over one hour.
  • All vapour release (no-liquid pool).
  • No momentum effects (no initial velocity for release).
  • Ground level release and receptors.
  • No deposition or reaction of cloud.
  • Neutrally buoyant cloud.
  • Urban dispersion coefficients.
  • No mitigating design or operating features to limit the rate or duration of the release or minimize its transport beyond the facility boundary.

OSHA regulates flammable liquids and gases under certain conditions, with a threshold of 4,545 kg (10,000 lbs).

Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: