Risk Assessment for Alternative Refrigerants Dr. Reva Rubenstein ICF Consulting Mr. Dave Godwin U.S. EPA

What is Risk Assessment? NAS definition Hazard Dose Response Exposure Assessment Risk Characterization

Limits Derived from Toxicity Values for Refrigerants Refrigerant Acute toxicity by inhalation exposure in the rat (ppm) Cardiac sensitization response, LOAEL, from inhalation in the dog (ppm) Recommended exposure limit, time-weighted average (ppm) HCFC-22220,000 (4-hr, LC-50)50,0001,000 (8-hr) HFC-134a567,000 (4-hr, ALC)75,0001,000 (8-hr) HFC-152a383,000 (4-hr, ALC)150,0001,000 (8-hr) CFC-12600,000 (2-hr, LC-50)>50,0001,000 (8-hr) CF 3 I , (AEL, EPA) CO 2 657,190 (15-min (LC-50)not applicable5,000 (8-hr) Butane280,000 (4-hr, LC-50)150, (8-hr) Isobutane570, min, LC-50)50, (10-hr) Note: LOAEL = lowest observed adverse effect level; LC-50 = lethal concentration for 50% of the population; ALC = approximate lethal concentration.

Flammability of Refrigerants Varying degrees of flammability CO 2 not flammable HFC-152a slightly flammable Hydrocarbons highly flammable

Why is Risk Assessment Difficult for MACs? Don’t have exposure information Scenarios can vary (technicians and general public) Fault tree approach

Fault Tree Definitions Definitions

Small Leaks Most refrigerant leaks into passenger compartments are too small to cause significant exposures Leak sites can become larger over time Measured leak rate in an evaporator increased 30% after 7 months

Medium Leak Definition Leak rate high enough to cause refrigerant concentrations to exceed recommended exposure limits Leak rate low enough to avoid easy detection by vehicle occupants and service technicians Exposure duration up to several hours

Medium Leak Causes System with leak into passenger compartment is recharged with refrigerant Survey indicated leaking systems are recharged   Leaks not identified   Leaks identified, recharge chosen Medium leak may occur suddenly

Refrigerant Accumulation Inside Parked Vehicle Testing showed that leaking refrigerant is not well mixed with air in the passenger compartment when the air blower is off Leaking refrigerant flows downward to the bottom of the evaporator housing and out through the condensate drain

Worst-case Conditions for Medium- Leak Exposure Refrigerant leak rate up to 3 grams/min Air blower on Air control in recirculation mode Doors and windows closed Vehicle speed low Small passenger compartment volume

Refrigerant Concentration in Passenger Compartment

Exposure due to Leak Following Recharge

Exposure due to Sudden Medium Leak

Large Leaks Caused by collisions Also caused by catastrophic failures of evaporators Survey indicated evaporators can rupture Vehicles usually not occupied when evaporators rupture Exposure duration short

Refrigerant Leakage from Evaporators

Exposure due to Sudden Large Leak

Exposure due to Leak Caused by Collision

Exposures of Service Technicians Survey indicated that burst hoses, o- rings, and sticking automatic shut-off valves can cause large releases of refrigerant Exposure duration short Estimated number of exposures in U.S. due to sudden leak: 135,000/yr

Exposure to Service Technicians

Overall Fault Tree

Risk Analysis Summary for Vehicle OccupantsEventExposures per year Exposure Conc. (ppm) Exposure Duration Medium leak after recharge 1,3462,000-18,000 5 min – 4 hr Sudden medium leak 3262,000-18,000 5 min – 4 hr Leak caused by collision 1,913 40, ,000 1 s – 5 min Sudden large leak 3 40, ,000 1 s – 5 min Total3,588

Availability of Data on Refrigerant Flammability and Compartment Concentrations FlammabilityConcentrations CO 2  ? CO 2  ? HFC-152a  ? HFC-152a  ? HFC-134a   HFC-134a   Hydrocarbons ?? Hydrocarbons ??

Conclusions Fault tree tells us most exposures are within acceptable limits Engineering can mitigate exposure Reducing Charge Size Reconfiguring cooling system Increasing airflow/intake Need more studies

References Amin, J. et al. Safety Aspects of an A/C System with Carbon Dioxide as Refrigerant. SAF Subcommittee Safety of Refrigerant Systems. Eyer, Peter. Toxicological Impacts of Enhanced Carbon Dioxide Concentrations on Human Health. Jetter, James J. et al Fault Tree Analysis for Exposure to Refrigerants Used for Automotive Air Conditioning in the United States. Risk Analysis, Vol. 21, No. 1. Jetter, James J. et al Refrigerant Concentrations in Motor Vehicle Passenger Compartments. ASHRAE Transactions: Research, 107, Pt. 2, Dupont. Dymel 152a Hydrofluorocarbon 152a. Technical Information ATB EPA Office of Pesticides Programs Label Review Manual.