Applying Refrigerant Codes
Administering limits for the amount of refrigerant that can be discharged into a space in the event of a leak
Some years ago, two young and inexperienced technicians were called to work on a large refrigerant system. The system was not working properly because of an incorrectly installed valve. In their attempt to fix the system, the technicians caused a leak in the piping at the tank, which contained several hundred pounds of refrigerant. Being heavier than air, the refrigerant gas began displacing oxygen in the normal-sized mechanical room. Little did they know—refrigerant cannot be seen or smelled—the technicians were starting to suffocate.
Within a few minutes, one technician, who had been bent over the tank attempting to fix the valve, was unconscious on the floor. The other technician, who had been standing, observing the procedure, was conscious, but essentially asleep on his feet.
Fortunately, the door to the mechanical room had been left open, and enough refrigerant escaped to trip a smoke detector in the fire alarm system. (This was in the days before code-mandated refrigerant alarms and ventilation systems.) The alarm awoke the standing technician. What he saw was a sea of white fog—the refrigerant, under higher pressure in the tank, expanded through the pipe opening and condensed—from the floor up to his chest. He dragged the unconscious technician outside, where they both were able to recover.
This incident illustrates the danger posed by a refrigerant leak.
ANSI/ASHRAE Standard 15, Safety Standard for Refrigeration Systems, ANSI/ASHRAE Standard 34, Designation and Safety Classification of Refrigerants, and the International Mechanical Code (IMC) define the levels of refrigerant discharge at which poisoning and suffocation occur. In particular, ANSI/ASHRAE Standard 34 defines refrigerant-concentration limit (RCL) and oxygen-deprivation limit (ODL).
RCL is the amount of refrigerant released into a normally occupied, enclosed space beyond which acute toxicity is expected. Typically, it is expressed in pounds per thousand cubic feet or parts per million. For example, R-410A, a refrigerant commonly used in variable-refrigerant-flow (VRF) systems, has a RCL of 26 lb per thousand cubic feet or 140,000 ppm. For institutional occupancies where “occupants cannot readily leave without the assistance of others,” the threshold is half that.
ODL is the concentration of a refrigerant or other gas resulting in insufficient oxygen for normal breathing. For refrigerant gas, ODL is 140,000 ppm at altitudes below 3,300 ft, 112,000 ppm at altitudes of 3,300 ft to 4,920 ft, and 69,100 ppm at altitudes above 4,920 ft.
Refrigerant fills a room similar to the way water fills a bathtub: from the bottom up. The incident involving the two technicians is a clear example of this: The technician who had been bent over the tank was unconscious because of the higher concentration of heavier-than-air refrigerant near the floor. Codes do not directly address how to apply this non-homogenous dispersion of refrigerant gas in a space. Nor do they directly address how to translate pounds of refrigerant to a room volume or area for easy application. These are challenges facing design engineers and contractors.
The problem can be broken down by addressing RCL and ODL separately and considering the type of refrigerant system (i.e., larger system located in a mechanical room or smaller system located in an occupied space).