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

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.


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


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


14


15

Air blower on16

Aircontrol in

recirculationm ode

17


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


caused by collision18


19

Occupantsurvivescollision

20

9 x 10 /yr-6

0.99 0.9

22.5 m illionvehiclesserviced

1

Exposure toservice technicians

in U.S.


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


Occupantin passengercompartm ent

14


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


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


leak

1 x 10 /yr-8

3 x 10 /yr-4

4 x 10 /yr-5

Exposure due to Leak Caused by Collision


collision

8 x 10 /yr-6




19


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


in U.S.


per vehicle

135,000/yr

0.006/yr

0.001/yr0.005/yr


equipment3


servicing2

Overall Fault Tree


in U.S.


3,600/yr

150 m illionvehicles

4

1.59occupantsper vehicle

51.5 x 10 /yr-5

Sudden largeleak in pass.com partm ent

11


12


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


7


8

Air blower on9

Aircontrol in

recirculationm ode

10


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




14


15

Air blower on16

Aircontrol in

recirculationm ode

17


1 x 10 /yr-4

0.3

0.95 0.99 0.2

0.19


collision

8 x 10 /yr-6




19


20

9 x 10 /yr-6

0.99 0.9

22.5 m illionvehiclesserviced

1


in U.S.


per vehicle

135,000/yr

0.006/yr

0.001/yr0.005/yr


equipm ent3


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.

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

Documents

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