Annex to chapter 2 - safety standards and regulations

Annex to chapter 2 - safety standards and regulations

Within the RAC industry, a different classification scheme is applied, where most refrigerants are assigned a safety classification, which is a function of toxicity and flammability. The classification scheme is adopted by such standards as, ISO 817 and draft EN 378. An overview of this was given in section 2.1.4, see also Table 2-2.

The toxicity classification is based on whether toxicity has or has not been identified at concentrations of less than 400 ppm by volume, based on data used to determine the threshold limit value – time weighted average (TLV-TWA) or consistent indices. There are two toxicity classes:

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  Class A: no chronic toxicity effects have been observed below 400 ppm
  
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  Class B: chronic toxicity effects have been observed below 400 ppm
  

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  Class 1: do not show flame propagation when tested in air at 60°C and standard atmospheric pressure
  
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  Class 2L: as Class 2 but with a (laminar) burning velocity of less than 0.10 m/s
  
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  Class 2: exhibit flame propagation when tested at 60°C and atmospheric pressure, but have a LFL higher than 3.5% by volume, and have a heat of combustion of less than 19,000 kJ/kg
  
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  Class 3: exhibit flame propagation when tested at 60°C and atmospheric pressure, but have an LFL at or less than 3.5% by volume, or have a heat of combustion that is equal to or greater than 19,000 kJ/kg
  

Typically, a “higher” the classification – that is toxicity Class B instead of Class A, and flammability Class 3 instead of Class 1 – means that the refrigerating system has more onerous design requirements associated with it, in order to handle the higher risk presented by the refrigerant.

The lower flammability limit (LFL) of flammable refrigerants is typically applied as a constraint to the amount of refrigerant that can be released into a room or enclosure, as it represents the smallest quantity that, when in the presence of an active source of ignition, could sustain a flame.

The acute toxicity exposure limit (ATEL) of any refrigerant may also applied as a constraint to the amount of refrigerant that can be released into a room or enclosure, as it represents the smallest quantity that could impose adverse toxicological effects onto occupants.

There is a further safety measure for the application of refrigerants, termed the practical concentration limit (PL). This represents the highest concentrations level in an occupied space which will not result in any escape impairing (i.e., acute) effects. Thus, it is principally, the lowest “dangerous” concentration of a refrigerant, with a safety factor applied. The estimation of PL is based on the lowest of the following:

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  Acute toxicity exposure limit (ATEL), based on mortality (in terms of LC50) and/or cardiac sensitisation, and/or anaesthetic or central nervous system (CNS) effects
  
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  Oxygen deprivation limit (ODL)
  
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  20% of the lower flammability limit (or 25% in ASHRAE 34)
  

Unlike conventional refrigerants, almost all of the low GWP refrigerants have safety characteristics, which demand greater attention, such as flammability, toxicity and higher operating pressures. Safety standards (and industry codes of practice) provide guidance to offset the additional risks posed by the more hazardous characteristics of the substances.

Although these safety standards cover requirements for flammable refrigerants, it is important to highlight that in many countries specific standards for equipment using flammable gases are available and are generally linked to legislation. For example, in Europe products which are placed on the market (except for those that are exempt) and that use flammable gases (including refrigerants) must meet the essential health safety requirements (EHSRs) of the Atex product directive (94/9/EC). By following the Atex harmonized standards, there is a presumption of conformity. Since none of the AC&R safety standards are harmonized to Atex, safety standards such as EN 1127-1 can be used for the evaluation of flammability safety; provided that AC&R equipment meets the requirements of such standards then deviations from the AC&R standards is acceptable if equivalent safety is demonstrated (for example, where larger refrigerant charges are needed.) In addition to meeting the EHSRs, the general approach prescribed by flammable gas standards and regulations is summarised:

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  Identification of explosion hazards and determination of the likelihood of occurrence of a hazardous atmosphere;
  
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  Identification of ignition hazards and determination of the likelihood of occurrence of potential ignition sources;
  
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  Estimation of the possible effects of an explosion in case of ignition;
  
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  Evaluation of the risk and whether the intended level of protection has been achieved;
  
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  Consideration of and application of measures to reduce of the risks
  

Table A2-3: Summary of PL and charge size limits for selected refrigerant and occupancies according to ISO 5149

Note: Allowable and maximum charges are per individual refrigerant circuit

Note: The values provided within this table are indicative and determination of refrigerant charge size limits for particular types of systems and installation locations requires the use of the standard and the values within this table should not be taken as a substitute.