A2L Essentials Issue 3: Mitigation Requirements 

One of the most popular options for handling the approaching low GWP regulations is switching to A2L refrigerants. Due to A2L’s mild flammability risk, doing so requires additional mitigation requirements.

A unit using a A2L refrigerant must meet all the requirements set forth by the UL. The UL (Underwriters Laboratories) is a private organization that is federally approved by the government to preform safety testing. A unit does not necessarily need to be UL certified to be legal, but the safety rating is critical for businesses and manufacturers wishing to follow best practices. UL certification officially demonstrates that a product is safe for use.

Due to A2L’s mildly flammable nature, there are extra precautions that the UL has required regarding the leak sensing and controls within in a A2L unit. One such regulation is that of the A2L safety kit. This safety kit includes a vacuum pump, leak detector, recovery machine and regulator.

Mitigation involves reducing the potential risks of A2L flammability. A2L’s require monitoring leak sensing and mitigation exhaust thresholds. Such regulations are critical to ensure efficiency, compliance, and safety.

The UL Lists requirements of refrigerant charge limits and outlines mitigation practices for installing products, mandates use of equipment that prohibits leak potential and allowed for charge limits in A2Ls of almost 200 pounds via 3 mitigation categories.

UL mitigation 60335-2-89, established (3) refrigerant charge limit thresholds for A2L refrigerants. These thresholds depend on both the lower flammability level established for the respective refrigerant and the application’s respective room volume. Therefore, it is critical to realize that these charge limits will vary depending on the A2L refrigerant.

The maximum charge for each charge limit, distinguished as “m1”, “m2” and “m3,” in the standard helps explain if additional mitigation practices are required. If the leak threshold established by the standard calls for 25% of the lower flammability level, then the alarm and mitigation requirements will be executed.

 For walk-in cooler/freezer unit coolers:

• Below and up to “m1” threshold charge, the equipment does not require mitigation practices
• Between “m1” and up to “m2” threshold charge, the equipment requires mitigation practices with increasing demands

These mitigation practices outline that...

• If between “m1” and “m2,” air circulation is constant and triggered by refrigeration detection (leak sensor, controls, etc.)
• If between “m2” and “m3,” additional exhaust ventilation is triggered by refrigerant detection (leak sensor, controls, etc.)
• If at “m3,” then you have reached the max allowable limit

For all refrigeration OEMs the product limits-of-use are based on the number of walk-in cooler/freezer cubic feet that need to be refrigerated. This will need to be clearly communicated and labeled. Additionally, there is an up to “m3” threshold. Mitigation practices require sites to install additional ventilation to help exhaust an A2L leak. Most mitigation zones will require shut-off valves to isolate the equipment.

Mitigation levels can change dramatically depending on room size, unit charge, and refrigerant. Be sure to consult an application engineer to make sure your unit complies with all regulations.  

Additionally, the UL has outlined the following mitigation categories based on applicability limits.

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