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### FAULT-TREE ANALYSIS OF THE USE OF HCR-188C IN COMBINATION REFRIGERATOR/FREEZERS AND WINDOW AIR CONDITIONING UNITS March 12, 2008 Draft Annotated Outline

I. Executive Summary

II. Introduction and Background - HCR-188C will be used in new appliances only - Will be used at low charge rate compared to other refrigerants - Charging of existing and older appliances will not be a registered use - Overall benefit as a “green” alternative refrigerant for these applications - Intended to replace fluorocarbon refrigerants - Compatible with materials found in refrigeration systems - Will be handled by trained and certified technicians only - HCR-188C will not be available to the general public for DIY activities - Guidelines have been developed for safe use of HCR-188C (Attachment. A)

III. Hazard Overview of HCR-188C - Physical chemical properties - Toxicological benchmarks - Flammability limits

IV. Summary of Test Data Supporting Charge Rates and Other Features - Refrigerator/freezer comparison test of R134a vs. HCR188C (Intertek) - Window AC unit test R22 vs. HCR188C (Intertek) - Determination and selection of optimum charge rates for assessment

V. Model Appliances for Study

A. Design of Combination Refrigerator/Freezer - Basic refrigeration system - Manufacturer’s data - Electrical components of concern for refrigerator/freezer B. Window Air Conditioning Unit - Basic air conditioning system - Manufacturer’s data - Electrical components of concern for window air-conditioning system

VI. Parameters and Data Sources

A. Residential parameters - Location of appliances - Room size(s) per NAHB surveys - Air exchange rates (Pandian et al. 1998); national median = 0.5 ACH2 B. Appliance parameters - Charge rates and justification - Cycle durations - Appliance capacity (Btu/hr) - Temperature differential across evaporator - Evaporator/condenser parameters - Air flow/vent ducting/fan recirculation flow rate (AC only)

C. Component failure rates and event probabilities – values and sources - Sources and locations of leaks - Initial pressure prior to leak - Refrigerant leak rates (pinhole leak scenario, catastrophic loss scenario) - Previously-reported component failure rate values (e.g., ADL 1991) - Updated component failure rates - Relationship between charge size and failure rate - Sources and locations of sparks - Appliance spark source strength - Other spark source strength/location in room (e.g., light bulbs, switches)

D. Occupational Parameters (During servicing) - Following standard guidelines and procedures - Warnings on flammability and avoidance of spark/flame sources - Directions on PPE (eye and skin protection) - Exposure scenario for trained technician only (HCR-188C is being registered for professional use only) - Room (shop) size and air exchange rate

E. Updated Fire Risk Data - Historical fire risk - Kitchen fires by cause - Residential fires (all causes and by source)

VII. Fault Tree Methodology and Considerations

A. Fault Tree Analysis For Recovery of HCR-188C During Servicing - Most recovery events will occur in product service centers - Recovery event in residential setting would be worst-case - 8 Connect/disconnect cycles per 8-hour shift (per AIHS assessment) - Reference to guidelines for HCR-188C in refrigeration and AC systems - Work conducted only by EPA-certified technician - Use the EPA-approved adaptor connectors and cylinder connectors only - Component probabilities of line/fitting/gasket/seal failures - Identify pathways and “AND”/“OR” gates3 B. Fault Tree Analysis For Charging With HCR-188C Following Servicing - Most recharging events will occur in product service centers - Recharging event in residential setting would be worst-case - 8 Connect/disconnect cycles per 8-hour shift (per AIHS assessment) - Reference to guidelines for HCR-188C in refrigeration and AC systems - Work conducted only by EPA-certified technician - Use the EPA-approved adaptor connectors and cylinder connectors only - Component probabilities of line/fitting/gasket/seal failures - Identify pathways and “AND”/“OR” gates

C. Fault Tree Analysis For Consumer Use of Window Air Conditioner - Average probability release w/ AC “OFF”, fan “OFF”, & vent “OPEN” -Average probability release w/AC “ON”, fan “LOW”, vent “CLOSED” - Average probability release w/ AC “ON”, fan “HIGH”, vent “CLOSED” - Worst case analysis for ruptured evaporator or evaporator input line

D. Fault Tree Analysis For Consumer Use of Refrigerator/Freezer - Average probability of release (pinhole leak) - Worst case probability of release (rupture of evaporator or input line) - Probability of over-pressurization of interior compartment

VIII.Fault Tree Diagrams and Results - Example CAD drawings of fault tree diagrams for average case -Average number exposures/year to refrigerant (occupational, consumer) -Worst case frequency of exposures with ignition source present - Conditions required for fire/explosion - Predicted frequencies with 100 percent market share - Predicted frequencies with realistic market share (per maximum market share associated with an individual refrigerant) - Tabular summary of failure data and results - Routine (average) and (worst case) frequency by appliance type - Fire-explosion frequency by appliance type

IX. Discussion and Conclusions - Comparison of HCR-188C results to fault tree analyses on other refrigerants - Safety valve not needed for appliances due to low overall failure probability and low amount HCR-188C used. - Implications of Guidelines (Attachment A) for safe use of HCR-188C - Put results in context with predicted room concentrations (Attachment B). - Put results in context of release to small room relative to what is required to reach lower limits of flammability, including source proximity considerations - Incremental (%) increase in kitchen and total residential fires (all sources) - Put risks in perspective relative to everyday risks - Sources of conservatism in the assessment - Sources of uncertainty in the assessment4 ATTACHMENT A: Guidelines for Using HCR-188C in Refrigeration/Air Conditioning

ATTACHMENT B: Service Technician/Consumer Exposure Assessment to HCR-188C Associated With Its Use in Residential Refrigerators/Freezers and Window Air Conditioning Units