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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 ACH
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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” gates 
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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 assessment
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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