Study shows HC charge-limit scenarios

A study by the Fire Protection Research Foundation (FPRF) has determined safe propane charge limits for self-contained display cases in a range of settings.

For example, the study showed that a 1000 g charge in an appliance in a big box grocery store is comparable in safety to a 150 g charge in a small commercial kitchen.

The study focused on the flammability hazards inherent in closed cases in commercial and retail kitchens. Its findings are significant because they indicate that it is safe to raise the charge limit of propane for wider use in commercial refrigeration under certain conditions. Currently, the Environmental Protection Agency caps the charge limit for propane in commercial appliances at 150 g.

Scott Davis, principal engineer for Gexcon US, presented the findings of the study in a session called “Understanding the Fire Hazard of Class A3 Refrigerants” at the Food Market Institute’s Energy and Store Development conference in Orlando, Fla., on September 25. The FPRF, an affiliate of the National Fire Proction Association, Quincy, Mass., was supported in the research project by co-leaders Target Corp. and the North American Sustainable Refrigeration Council (NASRC).

“The need to increase this limit is growing as lower GWP refrigerants are required,” Davis said.

In a summary slide, Davis listed the following propane charges in various commercial settings, each having the same risk factor as a 150 g charge in a small commercial kitchen:

• Up to 300 g in a 2,507 ft³ deli or a 6922 ft³ kitchen
• Up to 600g in a 3178 ft³ market
• Up to 1000g in a 36127 ft³ big box grocery store

 
Assessing fire risk

The driving force of the study was to assess the fire risk involved with larger charges of A3 (flammable) refrigerants to determine if they can be used in a wider range of applications. Larger allowable charge sizes, Davis pointed out, equate to larger equipment that can run on R290. He estimates that the charge limit for propane will be raised in the near future.

“[The] hydrocarbon limit is likely to move to 500 grams by 2018 in International Standards,” Davis said.

In fact, this week, the International Electrochemical Commission may be voting on a proposal to increase the charge limit for flammable refrigerants in commercial applications above 150 g at a meeting in Vladivostok, Russia.

In order to evaluate the risk posed by increasing the charge limit of propane, the study looked at both the probability of an event occurring and the possible consequences of such an event.

There were two main types of propane leaks that were observed. The first was a high-pressure jet – a short duration, high momentum and low-charge leak ­– where the propane was diluted when the charge size and room volume were scaled properly. The ignition risk for this type of leak was centered on the location of the leak.

The next leak type resulted in the settling of heavier-than-air propane at the ground level – a bigger leak with low momentum and larger charge. Without a condenser fan, flammable volumes were observed to accumulate at floor-level and pose an ignition risk.

Notably, both leak types were observed in test settings where there was no mitigating mechanical ventilation. With a condenser fan on in a properly scaled room, it’s possible to mitigate risks so that the propane mixes and does not reach flammable levels even at a 600g charge.

“The condenser fan prevented ignition in all events,” Davis said.

A condenser fan, early detection system, and properly scaled room, Davis said, are the key factors that will facilitate a safe increase of the propane charge limit.