EPA – CRP1234 Meeting

Presentation Outline

 Overview of CRP Fault Tree Analysis

Sensitivity Analysis

 New thoughts from CRP members since 

11/20/09 meeting

 Risk Comparison R134a – HFO-1234yf

 Stakeholders arguments regarding the 

proposed rule

 Status of new SAE standards

 Comments on UBA report

1
Fault Tree Analysis 

Overview

2

Tom Lewandowski, Ph.D., DABT

Gradient LLC

Seattle, WA
Tables 2-4 (1234yf) and 5-4 (R-744) in Phase III 

Report explain scenarios that were evaluated via 

FTA

3
Table 2-5 in Phase III Report explains how 

CRP1234 considered key fault tree scenario 

conditions

4
Attachment S contains detailed collision 

data that support the FTA assumptions

 Based on OEM interpretation of GIDAS and Delphi 

collision data

5
Attachments A (1234yf) and B (744) contain 

the basis and values for all FTA inputs...

6
As well as the fault trees 

themselves

 Trees for HFO-1234yf – 45 pages

 Trees for R-744 – 12 pages

NOTE:

The first page of each set 

of trees shows the 

various subtrees being 

added. This is an artifact 

of the software but should 

be disregarded. Some 

subtrees have different 

denominators (per year, 

per operating hour, per 

hour vehicle service) and 

should not be added.

7
Risk driver trees both involve 

operating vehicles, have the 

same denominator, and can be 

added

8

Results of some, but not all, branches can be added

All trees involve 

operating vehicles, 

have the same 

denominator, and can 

be added

Adding not possible 

but also not 

necessary because 

risk is dominated by 

single scenarios
Fault Tree Structure: Example

9

Speed independent event

Speed dependent branches
Page 15, High Speed Branch Common factors for all 

high speed collisions

Inputs for all high speed 

frontal collisions

Inputs for all high speed 

side collisions

Transfer to preceding slide

10
Non-Collision related trees are generally 

simpler in structure (i.e., single sheet)

11

Inverse gate (1-X): This tree requires 

the probability occupants stay in 

vehicle, the inverse (occupants leave 

vehicle) is used elsewhere
FTA Additional Comments

 Some collision trees share very similar but not 

identical inputs

 Thus some of the fault tree pages will look similar but 

have important differences

 Example - HF4.2 and HF5

 EV and Hybrid vehicle types are not addressed in 

this Risk Assessment

 Technology is still evolving

 OEMs will perform risk assessments of their specific 

designs

 No new general use conditions are needed

12
2. Sensitivity Analysis

 Evaluated several parameters where OEMs were 

uncertain

 Changed parameters to the alternative value and looked 

at overall impact on predicted top event frequency

 Looked at:

 Removal of secondary fires as a source of HF generation

 Change in hot surface temperature likely to ignite refrigerant

 Less conservative assumptions regarding collisions and engine 

surface temperatures

 Reduced “scrubbing” by rain/fog of air drawn into the cabin

 Increasing evaporator failure rate

13
14
Results of Sensitivity Analysis

 Most of the alternative values/scenarios had a 

minimal impact on the resulting top event 

probabilities

 Adopting less conservative assumptions 

regarding collisions, hot surfaces, and possible 

ignition sources reduced top event probabilities 

for refrigerant ignition by four orders of magnitude

 The sensitivity analysis demonstrates that the risk 

assessment is robust against changes in the 

input values

15
3. Risk Assessment Changes in 

Response to November 20 Meeting

 Changed references to “professional service 

worker/repair worker” to “certified service 

technicians”

 CRP recommends training according to J2845 and 

certification according to J2911

 CRP1234 Risk Assessment assumed this level of 

certification will occur

 Added comparison of risks to R-134a and R-12

 Improved documentation on fault tree 

development process

16
HFO-1234yf and R-744 are compared to 

R-12 and R-134a

LCCP not included because this was not a part of the risk assessment but EPA has results

17
Conclusions of CRP1234 risk 

assessment

 FTA expanded relative to Phase I and II 

risk assessments

 More detailed consideration of possible risk 

scenarios – greater confidence in results of 

the analysis

 Sensitivity analysis demonstrates that 

uncertainties in some input parameters have 

little impact on risk assessment conclusions

 Comparison of HFO-1234yf to R-12 and 

R-134a demonstrates an improved risk profile.

18
19

CRP1234 

Risk Comparison 

R-134a and HFO-1234yf

Dr. Chris Seeton

Honeywell
20

SAE CRP1234-3 Risks in Passenger Vehicles 

due to HF Exposure from HFO-1234yf

HF 3

HF 4

HF 4.2

HF 5

HF 6

HF 7.1

HF 7.2

HF 8.1

HF 9

HF 7.2

2.34 x 10-12

HF 4.2

2.25 x 10- 12

All other risk 

scenerios

SAE

CRP1234-3

Risk Scenerios

HFO-1234yf Risk of HF Exposure

There are two primary risk scenarios associated with the production of 

HF from a fluorinated refrigerant. The other risk scenarios are relatively 

insignificant for the basic comparison between R-134a and HFO-1234yf.

Exposure to HF above HBL 

due to vehicle fire caused by 

non-AC component failure 

in the engine compartment 

(former occupant, non collision)

Exposure to HF above HBL 

due to aspiration of HF from 

engine compartment

(occupant, collision)
21

R134a versus HFO-1234yf

 Extremely low risk for both refrigerants (same 

order of magnitude)

 HFO-1234yf is appropriate for use in MAC 

systems without use restrictions

Risk Scenario HFO-1234yf R-134a 

HF 7.2: Exposure to HF above HBL due to vehicle 

fire caused by non-AC component failure in the 

engine compartment (former occupant, non collision)

2.3 * 10-12 Same

HF 4.2: Exposure to HF above HBL due to aspiration 

of HF from engine compartment (occupant, collision) 2.3 * 10-12 Lower

Combined Risk 4.6 * 10-12 ~ 10-12
22

Major vehicle fires (HF 7.2)

 All fluorinated refrigerants, in a major vehicle fire 

will decompose to produce HF

 The amount of HF generated depends on the amount 

of refrigerant combusted 

 The amount of HF generated will be smaller for 

HFO-1234yf than R-134a for complete combustion

R-134a and HFO-1234yf have the same risk 

both generate HF
23

Aspiration of HF into Passenger 

Compartment (HF 4.2)

 Data indicates ignition of R134a+oil and 

HFO-1234yf+oil on hot surfaces

 Toyota, Hyundai and Honeywell report that 

R-134a+oil ignites >800oC on a hot plate

 INERIS reports that HFO-1234yf+oil ignites 

>750 ± 50oC on a hot surface

The risk is lower for R-134a compared to HFO-1234yf 

for this scenario
24

R134a versus HFO-1234yf

 Extremely low risk for both refrigerants (same 

order of magnitude)

 HFO-1234yf is appropriate for use in MAC 

systems without use restrictions

Risk Scenario HFO-1234yf R-134a 

HF 7.2: Exposure to HF above HBL due to vehicle 

fire caused by non-AC component failure in the 

engine compartment (former occupant, non collision)

2.3 * 10-12 Same

HF 4.2: Exposure to HF above HBL due to aspiration 

of HF from engine compartment (occupant, collision) 2.3 * 10-12 Lower

Combined Risk 4.6 * 10-12 ~ 10-12
25

Overall Risk Comparison Conclusions

 Use of HFO-1234yf in MAC systems poses a extremely low 

level of risk for all affected segments 

 Use of HFO-1234yf in MAC systems will have a negligible 

impact on current risks associated with vehicle operation or 

service with current design practices

 Recommendation for SNAP wording:

"HFO-1234yf MAC systems shall incorporate engineering 

strategies reasonably necessary to manage risks of injury 

and/or property damage caused by HFO-1234yf, similar to 

R-134a MAC systems. Such strategies shall be based on 

risk assessments using SAE J1739 (FMEA) or its 

equivalent."
26

Status of SAE Standards 

for 

HFO-1234yf

Ward Atkinson

Chairperson SAE ICCC
SAE Document Status Committee Ballot 

Type

Est. 

Comp. 

Data

Est. Pub 

Date

EPA 

Format

J639 Safety Standards for Motor Vehicle 

Refrigerant Vapor Compression Systems 

All 

Groups 28 Day 19-Mar 30-Apr 2-Apr

J2064 R134a and HFO-1234fy Refrigerant 

Automotive Air-Conditioning Hose and 

Assemblies

MAC 14 Day 5-Mar 19-Apr 19-Mar

J2099 Standard of Purity for Recycled HFC-134a 

(R-134a) and HFO-1234yf (R-1234yf) or Use in 

Mobile Air-conditioning Systems 

Fluids 28 Day 5-Mar 19-Apr 19-Mar

J2670 Stability and Compatibility Criteria for 

Additives and Flushing Materials Intended for 

Use in R-134a and HFO-1234yf Vehicle AirConditioning Systems

Fluids 28 Day 5-Mar 19-Apr 19-Mar

J2772 Measurement of Passenger Compartment 

Refrigerant Concentrations under system 

refrigerant leakage conditions 

OEM 28 Day 5-Mar 19-Apr 19-Mar

J2773 HFO-1234yf and R744 Refrigerant Standard 

for Safety and Risk Analysis for use in Mobile Air 

Conditioning Systems 

OEM 28 Day 5-Mar 19-Apr 19-Mar

J2842 HFO-1234yf and R744 Design Criteria and 

Certification for OEM Mobile Air Conditioning 

Evaporator and Service Replacements 

OEM & 

MAC 28 Day 19-Mar 30-Apr 2-Apr

J2843 HFO-1234yf 

Recovery/Recycling/Recharging Equipment for 

Flammable Refrigerants for Mobile AirConditioning Systems 

Service 14 Day 19-Feb 2-Apr 5-Mar

J2844 HFO-1234yf New Refrigerant Purity and 

Container Requirements Used in Mobile AirConditioning Systems 

Fluids 12-Mar 12-Mar

J2845 Technician Training for Safe Service and 

Containment of Refrigerants Used in Mobile A/C 

Systems (R-744, and HFO-1234yf) 

Service 14 Day 5-Mar 19-Apr 19-Mar

J2851 HFO-1234yf Refrigerant Recovery 

Equipment for Mobile Automotive AirConditioning Systems 

Service 14 Day 19-Feb 2-Apr 5-Mar

J2888 HFO-1234yf Service Hose, Fittings and 

Couplers for Mobile Refrigerant Systems Service 

Equipment 

Service 14 Day 5-Mar 19-Apr 19-Mar

J2911 Certification Requirements For Mobile Air 

Conditioning System Components, Service 

Equipment, and Service Technicians to Meet SAE 

J Standards 

MAC & 

Service 28 Day 19-Mar 30-Apr 2-Apr

J2912 HFO-1234yf Refrigerant Identification 

Equipment for Use with Mobile Air Conditioning 

Systems

Service 14 Day 19-Feb 2-Apr 5-Mar

J2913 HFO-1234yf Refrigerant Electronic Leak 

Detectors, Minimum Performance Criteria Service 28 Day 19-Mar 30-Apr 2-Apr

J2927 HFO-1234yf Refrigerant Identifier Installed 

In Recovery and Recycling Equipment For Use 

With Mobile A/C Systems

Service 28 Day 19-Mar 30-Apr 2-Apr
28

SAE CRP1234 

Response to UBA 

Docket Comment

Mary Koban

DuPont
Response to UBA Comment

 BAM testing found some HFO-1234yf ternary mixtures 

had LFL< 6.2 vol %. 

 Expected result when mixing HC with other refrigerant and/or air

 UBA expects HC’s in automotive workplace and/or from 

oil decomposition on engine and therefore HFO-1234yf 

should not be used with A/C.

 When oil breaks down, only small levels of HC’s are formed [PPM 

levels] 

 LFL of ethane and HFO-1234yf are given below:

Ethane LFL 2.4 vol %

HFO-1234yf LFL 6.2 vol % 

 Adding HFO-1234yf to ethane/air increases the LFL of 

the mixture above that of pure ethane, “quenching” the 

flammability of ethane
Results are for ethane/R-134a/air similar to 

ethane/HFO-1234yf/air

Response to UBA Comment

Further Comment will be submitted by DuPont and Honeywell
UBA test for HF

 UBA received a report by a German Institute IBExU 

(Institute for Security Techniques ltd.), 

 Temperature from 100°C to 500°C

 Qualitative measurements of HF were done with gas test 

tubes (Draeger). 

 Report shows HF formation at 300°C with a measurement 

of about 70 ppm HF

 CRP measured with a real vehicle at 450°C and 

obtained maximum levels of 7.5 PPM

 Exposure times and test method used by IBExU do 

not represent real world conditions

31