7.3 Safety Standards & Flammability: BS EN 378 & A2L/A3 Refrigerants

As the industry phases down high-GWP HFCs, engineers are increasingly working with alternative refrigerants that possess lower global warming potentials but present new safety challenges, primarily flammability. The overarching standard governing the safety and environmental requirements for refrigeration systems in Europe and the UK is BS EN 378.

BS EN 378: Safety and Environmental Requirements

BS EN 378 is a comprehensive, multi-part standard that applies to the design, construction, installation, operation, maintenance, and disposal of refrigerating systems. While not a law in itself, complying with BS EN 378 is generally accepted as demonstrating compliance with legal requirements like the Pressure Equipment Directive (PED) and HASAWA.

• Charge Limits: BS EN 378 establishes strict maximum refrigerant charge limits based on the toxicity and flammability of the refrigerant, the location of the equipment (e.g., basement vs. open air), and the category of occupancy (e.g., hospitals vs. industrial facilities).
• Leak Detection: The standard mandates that systems containing a high charge of refrigerant, especially in confined spaces or occupied areas, must be fitted with fixed, automatic leak detection systems that trigger alarms and potentially shut down the system or activate mechanical ventilation if a leak is detected.

ASHRAE Safety Group Classifications

To standardize the handling of different gases, refrigerants are classified according to their toxicity and flammability. The globally recognized classification system is the ASHRAE standard 34, which assigns a letter and a number to each gas.

• Toxicity (Letter):
  • A: Lower toxicity.
  • B: Higher toxicity.
• Flammability (Number):
  • 1: No flame propagation (Non-flammable at standard conditions).
  • 2L: Lower flammability (Mildly flammable, difficult to ignite, slow flame speed).
  • 2: Flammable.
  • 3: Higher flammability (Highly explosive).

Common Classifications:

1. A1 (Lower Toxicity, Non-Flammable): Traditional HFCs like R-134a, R-410A, and R-404A. While deemed "non-flammable," they can still decompose into toxic substances if exposed to a naked flame.
2. A2L (Lower Toxicity, Mildly Flammable): The new generation of HFOs (like R-1234yf) and lower-GWP HFCs (like R-32). They are flammable but require a high ignition energy to catch fire, and they burn slowly.
3. A3 (Lower Toxicity, Highly Flammable): Hydrocarbons (HCs) such as R-290 (Propane) and R-600a (Isobutane). These are highly explosive and require extreme caution, but they have excellent thermodynamic properties and a GWP near zero.

Working with A2L and A3 Refrigerants

The influx of A2L (R-32) and A3 (Propane) refrigerants demands a fundamental shift in working practices. Traditional A1 procedures are no longer sufficient. When performing installation, maintenance, or recovery on mildly or highly flammable systems, specific safety measures are mandatory.

1. Ventilation and Exclusion Zones

Before opening a system or beginning recovery, the working area must be well-ventilated to prevent the accumulation of flammable gas in the event of a leak.

• Temporary Exclusion Zone: An exclusion zone (typically a minimum of 3 meters, though BS EN 378 dictates specific calculations) must be established around the work area.
• Ignition Sources: Within this exclusion zone, all potential sources of ignition must be strictly prohibited. This includes naked flames, smoking, uncertified electrical equipment, and hot surfaces.

2. Spark-Free Tools and Equipment

Standard refrigeration tools can cause sparks (either electrical sparks from motors or mechanical sparks from dropping steel tools).

• ATEX/Spark-Proof Equipment: When working with A3 (and increasingly A2L) refrigerants, engineers must use specially rated, intrinsically safe equipment. This includes ATEX-approved vacuum pumps (with spark-free switches and motors), ATEX-approved recovery machines, and combustible gas leak detectors.
• Non-Sparking Hand Tools: Brass or beryllium copper hand tools should be used instead of standard steel to prevent mechanical sparks if a tool is dropped.

3. Safe Recovery and Brazing Procedures

• Flushing: Before brazing (which introduces an open flame) on an A2L or A3 system, the refrigerant must be completely recovered. Furthermore, the system must be rigorously purged with Oxygen-Free Nitrogen (OFN) to ensure absolutely no flammable vapors remain trapped in the pipework or compressor oil. Brazing must only occur while a slight positive flow of OFN is passing through the system to prevent oxygen ingress and eliminate the combustion triangle.
• Dedicated Cylinders: Flammable refrigerants must be recovered into specific cylinders that are rated and explicitly marked for flammable gases (often featuring a left-hand thread on the valve to prevent accidental connection to non-flammable systems, and a red collar/band).