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Skills Summary HVAC&R MODULE Skills 120 FLAMMABLE Workshop LOWER TOXICITY PROUDLY SPONSORED BY AIRAH REFRIGERANTS This Skills Workshop is taken from the Institute of Refrigeration’s 2018 Safety Code of Practice. The object of this code is to define minimum Skills summary requirements for safety in the design, construction and installation, ■ What? commissioning, inspection and maintenance of vapour compression Properties of flammable refrigerants as refrigerating systems utilising flammable, lower toxicity refrigerants. listed in the Institute of Refrigeration’s 2018 Safety Code of Practice. These are classified as Group A2L, A2 or A3 refrigerants. ■ Who? This section of the code deals with the properties of these refrigerants. Relevant for every person with responsibility through ownership, The code of practice is intended to apply within the United Kingdom. consultancy, design, construction, installation, commissioning, However, the information is of general use in Australia as well. Where decommissioning, operation, maintenance, appropriate, relevant Australian standards have been noted next to the inspection, repair, modification or testing of a compression refrigeration system. British standards. (LFL) and the Upper Flammability Limit (UFL) in Moisture solubility Relevant properties air and the Auto-Ignition Temperature (AIT). The Moisture is sparingly soluble in most refrigerants occupational exposure limit (OEL) indicates the of refrigerants at ambient temperature. The solubility decreases concentration of refrigerant in the atmosphere that as the temperature reduces and excess water Physical properties is allowable for continuous exposure during an can lead to the formation of ice or hydrate at the eight-hour working day. The PL for A2L, A2 and A3 Table 1 on page 17 shows some of the important expansion device, which could impair or stop the refrigerants is based on approximately 20% of the physical properties for the most common operation of the system. Moisture also increases LFL. Refrigerant detection devices should be set to flammable lower toxicity refrigerants. The normal the possibility of chemical reactions between the warn of concentrations of A2L, A2 or A3 refrigerants boiling point indicates the type of application for refrigerant, the oil and the system components and which approach the PL and the OEL. which the refrigerant should be used. The Practical in many refrigeration applications acids may form Limit (PL) of the refrigerant indicates the allowable The Figure below shows the pressure temperature which could damage the windings of hermetic or refrigerant charge related to the smallest human relationship of a selection of different refrigerants semi-hermetic compressors. Due to the chemical occupied space as defined in BS EN 378-1:2016. including Propane which is an A3 Flammable make-up of hydrocarbons, this is unlikely to occur Reference is made to the Lower Flammability Limit Lower Toxicity Refrigerant covered by this Code. with A3 refrigerants, but still applies to A2L and A2 refrigerants. Figure 1. Pressure temperature relationship of selected refrigerants 1000 Adsorbent desiccants (molecular sieves) which preferentially adsorb water in the presence of many refrigerants are generally applicable to most A2L, 100 A2 and A3 refrigerants provided the appropriate grades of adsorbent desiccant are selected. Conventional desiccants, such as activated alumina, ) 10 will adsorb moisture in the presence of most A2L, A2 and A3 refrigerants. However such desiccants ar(A) do not retain moisture at higher temperatures as 1 Atmospheric Pressure well as the molecular sieve materials. Moisture removed during operation of the refrigerating CO2 system may therefore be returned to the system Pressure (b 0.1 R-32 when it is switched off and warms up. It is strongly recommended that drier cores (or beads etc) Ammonia specifically designated for the refrigerant are used. Propane 0.01 R-134a Lubricants In general, blends containing A2L or A2 refrigerants are not soluble in mineral or alkyl-benzene oils. 0.001 Special synthetic lubricants are recommended. -120 -100 -80-60 -40-12 0 20 40 60 80 100120 140 The most common type of synthetic lubricant for Temperature (°C) use with A2L or A2 refrigerants is the polyolester April 2019 | www.airah.org.au/nation | HVAC&R Nation | 15 HVAC&R Skills Workshop oil (POE) (although the automotive industry Chemical properties and Excursions to concentrations above the commonly uses polyalkylene glycol (PAG) oils for potential hazards Occupational Exposure Limit values quoted in automotive air conditioning). It is a disadvantage Table 1 are permitted as defined by the short-term A risk assessment shall be carried out by a of these lubricants that they have a much greater exposure limit (STEL) where listed by the HSE or competent person prior to commencing any work. affinity for water than traditional mineral oils to other short-term limits as advised by refrigerant The following items should be considered – note the extent that they will absorb moisture from the manufacturers after risk assessment. atmosphere. They therefore have to be kept from this list is not exhaustive and a site specific risk assessment should be carried out. contact with the atmosphere as much as possible. The vapour of most refrigerants is colourless, odourless and denser than air. If inadvertently PAG oils have the additional disadvantage that they Reactivity are intolerant of trace quantities of chlorine. released to atmosphere it will initially collect at low A2L, A2 or A3 refrigerants do not react with steel, level, particularly in pits, trenches and basements. In general, pure A3 refrigerants can be used with copper, aluminium and brass in acceptably dry Suitable temporary forced ventilation which does a wider range of lubricants, particularly mineral refrigerating systems. Alloys containing more not provide a source of ignition shall be provided and alkyl-benzene oils. However, solubility than 2% magnesium will react with fluorine and to disperse the vapour rapidly. tends to be increased with A3 refrigerants chlorine atoms in A2L and A2 blends and so so it may be necessary to select a lubricant should only be used with pure A3 refrigerants. In Care shall be exercised on entering a pit, trench with a higher viscosity grade. Polyalphaolefin the presence of moisture, zinc and galvanised steel or basement where there is a possibility of a high (PAO) and polyalkylene glycol (PAG) are also are particularly susceptible to corrosive attack. concentration of refrigerant vapour. acceptable for use where approved by the compressor manufacturer. POE oils are also Thermal decomposition Fatal accidents involving refrigerants can occur acceptable but do exhibit an even higher A3 refrigerants are subject to thermal either as a result of asphyxiation or ignition. solubility with A3 refrigerants. It is a disadvantage decomposition at temperatures of the order of of these lubricants that they have a greater 450°C, and A2L and A2 refrigerants at temperatures Direct contact affinity for water than ordinary mineral oils and in excess of 250°C. In the presence of oil and other Where liquid refrigerants having boiling points therefore have to be kept from contact with contaminants they are subject to reaction and below zero Celsius at atmospheric pressure come the atmosphere as much as possible. decomposition at lower temperatures, particularly into contact with the skin or eyes, evaporation if impurities such as moisture are present in the may cause freezing of the skin or eye fluids and Care should be taken that the correct lubricant is system. Temperatures in refrigerating systems freeze burns may occur. Clothing saturated with selected for the application, for the compressor should be limited to about 135°C. Many A2L, A2 or liquid refrigerant may freeze to the skin. Higher and for the refrigerant used. Seek advice from the A3 refrigerants have low indices of compression, boiling point refrigerants have solvent actions compressor manufacturer if there is any doubt. which tend to produce low compressor discharge that can cause defatting and cracking of the skin. temperatures, although some can have higher Goggles, suitable temperature rated gloves and Materials compatibility discharge temperatures e.g., R32. other suitable clothing shall be worn whenever It is important to consider the compatibility of the there is a risk of exposure to refrigerant liquid. refrigerant and the compressor oils with system Since A3 refrigerants lack chlorine and fluorine materials such as plastics, elastomers, metals, etc. atoms there is no possibility of acid formation in the presence of moisture and therefore Potential sources of Virtually all common elastomer and plastic salt formation and subsequent blockage in refrigerant leakage materials used as ‘O’ rings, valve seats, seals appliances is unlikely. Thermal decomposition of The refrigerating system contains refrigerant and gaskets are compatible with A2L, A2 or A3 A3 refrigerants external to the system does not in both liquid and vapour states. It is possible refrigerants. Materials that are not compatible and produce harmful decomposition products, whilst under abnormal conditions for liquid refrigerant should not be used in HC systems include EPDM, decomposition of fluorinated refrigerants can to enter the compressor, for example by way natural rubbers and silicone rubbers. It should be produce toxic substances such as hydrofluoric acid of faulty valves or by overcharge of refrigerant noted that chloroprene
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