2021 Mechanical Code Committees Vote to Keep Restrictions for A2L Flammable Refrigerants

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UMC and IMC Committees Vote to Disallow Flammable Refrigerants in Direct Systems and Maintain Current Safety Restrictions.

2021 Mechanical Code Committees Vote to Keep Restrictions for A2L Flammable RefrigerantsOne of the hottest topics in the mechanical code world is that of flammable refrigerants and their applications. The issue is currently playing out in the model code arena.  In the United States, jurisdictions have a choice of two model mechanical codes. The Uniform Mechanical Code (UMC) is developed by the International Association of Plumbing and Mechanical Officials (IAPMO); the International Mechanical Code (UMC) is developed by the International Code Council. 

Uniform Mechanical Code

The IAPMO recently held their Uniform Mechanical Code (UMC) technical committee hearings to update the 2021 edition of the UMC in Denver Colorado on May 1 and 2. Several proposals would have allowed A2L (flammable) refrigerants to be used in direct, high probability systems in residential and commercial buildings.

It was a divided house as producers and manufacturers presented their respective cases on both sides of the issue. The committee allowed discussion to proceed for approximately 2 hours and experts from all facets of the industry debated and informed the committee’s decision makers. In the end, the committee sided with those who presented safety concerns about the introduction of flammable refrigerants before the risks were appropriately addressed. Assuming the committee’s decision is final, the 2021 edition of the Uniform Mechanical Code will not allow flammable refrigerants, including A2L refrigerants in direct air conditioning systems.

International Mechanical Code

The International Code Council (ICC) completed their 2021 International Mechanical Code (IMC) development process last year and also rejected code change proposals that would have loosened the restrictions on flammable refrigerants.


At both ICC and IAPMO mechanical code development hearings, a handful of manufacturers and industry associations advocated for enabling language to permit A2L refrigerants to be used in high probability direct air-conditioning systems for human comfort.  They offered a great deal of testimony in support of their proposals. In the end, both technical committees came to the same conclusion: it is premature to allow flammable refrigerants to be widely used in direct, high probability systems.

Although they are forbidden in direct systems, both codes allow their use in indirect systems located in refrigeration machinery rooms due to the known attributes of such spaces, such as, size and volume of the room, current availability of reliable detection and ventilation and dilution rates.

Research is currently underway to inform those who are developing equipment and installation standards; this research includes an assessment of refrigerant detector characteristics; post-ignition risk assessment; effectiveness of mitigation strategies being proposed; ignition potential from electrical devices and more. This research should be used to develop equipment and installation standards. When the research is finished, the installation standards and equipment safety standards are completed, and the refrigerant technicians are trained, it’s likely the code development committees will look more favorably on the use of flammable refrigerants in these applications.