scope:

Background:

The refrigerant concentration as described in Section 7.2 "shall not exceed" the ANSI/ASHRAE Standard 34 Refrigerant Concentration Limits (RCLs). The total leaked refrigerant mass divided by the volume of the occupied, contaminated room (plus uncontaminated spaces connected by "permanent openings or HVAC ducts" per Section 7.3) is held at or below the RCL. Subsequent to a leak, the refrigerant concentration in the occupied, contaminated room into which the leak occurs could exceed the RCL. Concentrations equalize between the contaminated room and connected uncontaminated spaces at a rate determined by the rate of refrigerant transfer. Standard 34 RCLs are carefully selected to "reduce the risks of acute toxicity, asphyxiation, and flammability hazards", and exceeding an RCL elevates the risk. RCLs are sometimes controlled by Acute Toxicity Exposure Limit (ATEL), which can be associated with a time duration. One source suggests that a 30 minute maximum exposure at the RCL would not be inconsistent with underlying assumptions in Standard 15.