To replace ODS critical to military refrigeration and fire suppression applications, industry initially introduced HFCs as alternatives. Military organizations tested, evaluated, and implemented some of these chemicals in applications where they met performance, flammability and toxicity requirements. However, HFCs are considered greenhouse gases, and many of them have high GWP. As a result, these first generation, high GWP ODS alternatives are now under scrutiny to be regulated globally.
The details of the global phase down are still being negotiated by the Parties to the Montreal Protocol, but the U.S. government and industry have already begun moving toward second generation ODS alternatives. The U.S. Environmental Protection Agency (EPA) has begun removing some high GWP HFCs from the Significant New Alternatives Policy (SNAP) list for applications where low GWP alternatives are available. The DoD represents only a small portion of the global refrigerant market, so there is a risk that industry could stop producing refrigerants and systems that meet military flammability and toxicity requirements.
Military applications must address three primary concerns: efficiency, toxicity, and flammability. Toxicity and flammability do not pose a significant safety threat in commercial applications, but make it highly unlikely that the proposed second generation ODS alternatives can be used in military applications without significant modifications.
Efficiency: It is important for the next generation of ODS alternatives to be as efficient as current systems. Even a very small decrease in efficiency would result in indirect greenhouse gas emissions from burning fossil fuels, which could far exceed any climate benefit from reducing direct emissions from refrigerants, in particular for large refrigeration systems on Navy ships.
Toxicity: The risk of toxic byproduct generation in strictly commercial HFC-based refrigeration applications is negligible, so little is known about the conditions that could lead to unacceptable toxicity risks for the military. Exposure to HFC breakdown products (i.e., hydrogen fluoride and carbonyl fluoride) can cause devastating injury and death in certain scenarios unique to the military. The Navy already requires that refrigerants used in submarines must not produce toxic breakdown products when exposed to the onboard atmosphere control systems (i.e., carbon dioxide scrubbers and carbon monoxide/hydrogen burners). Further, initial results of an Army Public Health Command study on acute inhalation exposure to gaseous hydrogen fluoride and carbonyl fluoride suggest that carbonyl fluoride may be more harmful relative to hydrogen fluoride than had been believed previously. The breakdown of HFCs tends to produce more carbonyl fluoride than the halons that they were implemented to replace.
Flammability: To replace the high GWP HFC-134a in mobile air conditioning applications, industry is trending towards unsaturated HFC-1234yf, which has low GWP but is known to have flammability properties that may pose an unacceptable threat to military applications. Navy refrigeration systems, for example, can be located near nuclear or conventional-powered machinery spaces on ships and submarines where no level of flammability is acceptable. In other 3 air conditioning applications, industry had been using blends of HFCs to reduce flammability. R-410a is a mixture of equal parts HFC-125, which is not flammable but has high GWP, with HFC-32, which is flammable but has relatively lower GWP. Industry is now looking towards accepting flammability risk in exchange for reduced GWP by using straight HFC-32 without blending it to reduce flammability. For some refrigeration applications, industry is looking towards very flammable hydrocarbon blends almost certainly not acceptable in combat scenarios and likely not in certain DoD fixed facility applications, such as rooftop air conditioning units that are unprotected from blast or impact.
