Streamlining safety standards for flammable refrigerants to enhance usability and clarity.

At the recent Herrick Conferences at Purdue University, the refrigeration short course, “The Transition to Flammable Refrigerants,” reviewed some recent research work on flammable refrigerants, including several ASHRAE-funded projects. The quality of work being conducted in this area is exceptional, but I was left with a growing feeling of dissatisfaction with the underlying foundation of this work, the safety standards that we use to design, install and maintain our systems.

For ASHRAE this is primarily ASHRAE Standard 15 and ASHRAE Standard 34, together with their recently refreshed ISO counterparts, ISO 5149 and ISO 817, respectively. I realize that the basis of these standards was laid down many decades ago when refrigerant choice was much simpler and the chemistry behind flammability and toxicity was less well understood. Since then we have spent thousands upon thousands of labor-hours piling complexity onto those early versions so that they are now virtually unrecognizable and virtually unusable for most ordinary folk. Surely there must be significant scope for a major overhaul of these documents to make them more accessible to the average contractor who has most to gain from an easy-to follow guide.

A prime example of this complexity is in the flammability classification itself. We originally recognized refrigerants as being “non-flammable,” “flammable,” and “highly flammable,” and the same terms are used by the national and international regulations that govern the labelling and transportation of flammable gases and liquids. The boundary between the different classes in the refrigeration codes was based upon two flammability characteristics; lower flammable limit (LFL, which is a measure of how likely it is that a flammable atmosphere can be created) and heat of combustion (HoC, which is a measure of how much damage will be done if a flammable atmosphere does ignite). Over the last decade an additional class, based on consideration of the laminar burning velocity of the ignited refrigerant has also been introduced. This was quickly followed by a major international effort to produce a standard for reliable, repeatable testing of the burning velocity—a standard that had never existed before because there had never before been any need for it. We now could classify refrigerants based only on burning velocity, without considering LFL and HoC and get exactly the same classification as before.

However this leads us neatly to a second problem of complexity—the boundaries between classes create artificial distinctions that are confusing and unhelpful in the real world. When blends are being formulated they are designed to give best performance while not exceeding the artificial line, whether that is to retain A1 rating or to be A2L but not A2. This means that something else, usually price, efficiency or global warming potential is sacrificed in exchange for the lower flammability rating. In the real world, flammability is a continuum dependent on factors not considered in the standard test that determines the classification. The ignition sources encountered in the real world are not completely emulated by the standard test, and other conditions such as humidity are not representative either. This leads to some odd situations. In tests at the University of Maryland, which were reported to the short course audience, some situations expected to be flammable were not and others expected to be benign were not. Perhaps the most disturbing was the effect of turbulence on the burning velocity. All of the standard tests are done with no turbulence, but as the students discovered, turbulence can increase the burning velocity by a factor of 10.

A third conundrum highlighted in the report of ASHRAE research project RP-1808 on the tightness of field-made mechanical joints is that we work to a far higher standard of integrity than any other industry serving the same customers. This is necessary to keep the refrigeration system working reliably and efficiently but it makes a nonsense of our leakage calculations when our extremely tight systems are installed alongside heating and cooking equipment which uses connectors with leak rates several orders of magnitude worse than refrigeration fittings and allows untrained amateurs (householders) to connect them using sloppy bayonet-type fittings. In contrast, for air conditioners, we calculate charge limits based on the flammability classifications and presume that all of that charge could enter the space simultaneously without any dilution.

I believe the whole system needs a major overhaul. We could, for example, completely get rid of flammability classes and charge limits and approach the whole topic from a risk assessment standpoint. As we consider that task I hope for one thing: please keep standards simple.