risk assessment for alternative refrigerants dr. reva rubenstein icf consulting mr. dave godwin u.s....
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Risk Assessment for Alternative Refrigerants
Dr. Reva Rubenstein
ICF Consulting
Mr. Dave GodwinU.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-22 220,000 (4-hr, LC-50) 50,000 1,000 (8-hr)
HFC-134a 567,000 (4-hr, ALC) 75,000 1,000 (8-hr)
HFC-152a 383,000 (4-hr, ALC) 150,000 1,000 (8-hr)
CFC-12 600,000 (2-hr, LC-50) >50,000 1,000 (8-hr)
CF3I --------- 4,000 150 (AEL, EPA)
CO2 657,190 (15-min (LC-50) not applicable 5,000 (8-hr)
Butane 280,000 (4-hr, LC-50) 150,000 800 (8-hr)
Isobutane 570,000 15-min, LC-50) 50,000 800 (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 CO2 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
Exposure tovehicle occupants
in U.S.
Exposure tovehicle occupants
3,600/yr
150 m illionvehicles
4
1.59occupantsper vehicle
51.5 x 10 /yr-5
Sudden largeleak in pass.com partm ent
11
Occupantin passengercom partm ent
12
Exposure due tosudden large
leak
1 x 10 /yr-8
3 x 10 /yr-4
4 x 10 /yr-5
Exposure due tosudden m edium
leak
1 x 10 /yr-6
Suddenm edium leakin passengercom partm ent
6
Occupantin passengercom partm ent
7
Doors andwindows closed
8
Air blower on9
Aircontrol in
recirculationm ode
10
Refrigerant m ixedwith breathing air
2 x 10 /yr-4
0.04
0.9 0.95 0.2
0.17
Exposure due toleak following
recharge
1 x 10 /yr-6
Leak in pass.com partm ent
following servicing13
Occupantin passengercom partm ent
14
Doors andwindows closed
15
Air blower on16
Aircontrol in
recirculationm ode
17
Refrigerant m ixedwith breathing air
1 x 10 /yr-4
0.3
0.95 0.99 0.2
0.19
Exposure due toleak caused by
collision
8 x 10 /yr-6
Leak in pass.com partm ent
caused by collision18
Occupantin passengercom partm ent
19
Occupantsurvivescollision
20
9 x 10 /yr-6
0.99 0.9
22.5 m illionvehiclesserviced
1
Exposure toservice technicians
in U.S.
Exposure toservice technicians
per vehicle
135,000/yr
0.006/yr
0.001/yr0.005/yr
Sudden largeleak in service
equipm ent3
Sudden largeleak in vehiclesystem during
servicing2
DefinitionsDefinitionsThe result of several initiating and/or contributing events through “and” or “or” gate with roles of occurrence either yearly or per dmeand
Numbers of components, serve as multipliers
“And” gate multiplies the rate of occurrence of the incoming branches
“Or” gate adds the rates of occurrence of the incoming branches
Contributing events with rules of occurrence per demand. Conditional on the prior initiating and contributing events having taken place.
Initiating events with yearly rates of occurrence
Fault Tree Logic Sympols
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 identifiedLeaks 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 Concentrationin Passenger Compartment
Exposure due to Leak Following RechargeExposure due to
leak followingrecharge
1 x 10 /yr-6
Leak in pass.compartm ent
following servicing13
Occupantin passengercompartm ent
14
Doors andwindows closed
15
Air blower on16
Aircontrol in
recirculationmode
17
Refrigerant mixedwith breathing air
1 x 10 /yr-4
0.3
0.95 0.99 0.2
0.19
Exposure due to Sudden Medium Leak
Exposure due tosudden medium
leak
1 x 10 /yr-6
Suddenmedium leakin passengercompartm ent
6
Occupantin passengercompartm ent
7
Doors andwindows closed
8
Air blower on9
Aircontrol in
recirculationmode
10
Refrigerant mixedwith breathing air
2 x 10 /yr-4
0.04
0.9 0.95 0.2
0.17
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
Sudden largeleak in pass.compartment
11
Occupantin passengercompartment
12
Exposure due tosudden large
leak
1 x 10 /yr-8
3 x 10 /yr-4
4 x 10 /yr-5
Exposure due to Leak Caused by Collision
Exposure due toleak caused by
collision
8 x 10 /yr-6
Leak in pass.com partm ent
caused by collision18
Occupantin passengercom partm ent
19
Occupantsurvivescollision
20
9 x 10 /yr-6
0.99 0.9
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
22.5 millionvehiclesserviced
1
Exposure toservice technicians
in U.S.
Exposure toservice technicians
per vehicle
135,000/yr
0.006/yr
0.001/yr0.005/yr
Sudden largeleak in service
equipment3
Sudden largeleak in vehiclesystem during
servicing2
Overall Fault Tree
Exposure tovehicle occupants
in U.S.
Exposure tovehicle occupants
3,600/yr
150 m illionvehicles
4
1.59occupantsper vehicle
51.5 x 10 /yr-5
Sudden largeleak in pass.com partm ent
11
Occupantin passengercom partm ent
12
Exposure due tosudden large
leak
1 x 10 /yr-8
3 x 10 /yr-4
4 x 10 /yr-5
Exposure due tosudden m edium
leak
1 x 10 /yr-6
Suddenm edium leakin passengercom partm ent
6
Occupantin passengercom partm ent
7
Doors andwindows closed
8
Air blower on9
Aircontrol in
recirculationm ode
10
Refrigerant m ixedwith breathing air
2 x 10 /yr-4
0.04
0.9 0.95 0.2
0.17
Exposure due toleak following
recharge
1 x 10 /yr-6
Leak in pass.com partm ent
following servicing13
Occupantin passengercom partm ent
14
Doors andwindows closed
15
Air blower on16
Aircontrol in
recirculationm ode
17
Refrigerant m ixedwith breathing air
1 x 10 /yr-4
0.3
0.95 0.99 0.2
0.19
Exposure due toleak caused by
collision
8 x 10 /yr-6
Leak in pass.com partm ent
caused by collision18
Occupantin passengercom partm ent
19
Occupantsurvivescollision
20
9 x 10 /yr-6
0.99 0.9
22.5 m illionvehiclesserviced
1
Exposure toservice technicians
in U.S.
Exposure toservice technicians
per vehicle
135,000/yr
0.006/yr
0.001/yr0.005/yr
Sudden largeleak in service
equipm ent3
Sudden largeleak in vehiclesystem during
servicing2
The result of several initiating and/or contributing events through “and” or “or” gate with roles of occurrence either yearly or per dmeand
Numbers of components, serve as multipliers
“And” gate multiplies the rate of occurrence of the incoming branches
“Or” gate adds the rates of occurrence of the incom ing branches
Contributing events with rules of occurrence per demand. Conditional on the prior initiating and contributing events having taken place.
Initiating events with yearly rates of occurrence
Fault Tree Logic Sympols
Risk Analysis Summary for Vehicle Occupants
EventEventExposureExposure
ss
per yearper year
ExposureExposure
Conc. (ppm)Conc. (ppm)Exposure Exposure DurationDuration
Medium leak after Medium leak after rechargerecharge 1,3461,346 2,000-2,000-
18,00018,0005 min – 5 min –
4 hr4 hr
Sudden medium Sudden medium leakleak 326326 2,000-2,000-
18,00018,0005 min – 4 5 min – 4
hrhr
Leak caused by Leak caused by collisioncollision 1,9131,913 40,000-40,000-
100,000100,0001 s – 5 1 s – 5
minmin
Sudden large leakSudden large leak 3340,000-40,000-100,000100,000
1 s – 5 1 s – 5 minmin
TotalTotal 3,5883,588
Availability of Data on Refrigerant Flammability and Compartment Concentrations
FlammabilityFlammabilityConcentrationsConcentrations
COCO22 ??
HFC-152aHFC-152a ?? HFC-134aHFC-134a HydrocarbonsHydrocarbons ?? ??
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. 2001. 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. 2001. Refrigerant Concentrations in Motor Vehicle Passenger Compartments. ASHRAE Transactions: Research, 107, Pt. 2, 99-107.
Dupont. Dymel 152a Hydrofluorocarbon 152a. Technical Information ATB-29. http://www.dupont.com/dymel/pdf/h64411.pdf.
EPA Office of Pesticides Programs. 1995. Label Review Manual. http://www.epa.gov/oppfead1/labeling/lrm/index.html.
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