BAM test report page 2 of 31 pages BAM-ref.: II-2318/2009 I 

0 Table of Contents 

0 Table of Contents................................................................................................................ 2

1 Scope ................................................................................................................................... 3

2 Safety characteristics, terms and definitions................................................................... 3

3 Work package 1: Explosion regions of ethane-refrigerant-air mixtures........................ 4

3.1 Introduction................................................................................................................... 4

3.2 Test procedure ............................................................................................................. 4

3.3 Results.......................................................................................................................... 5

4 Work package 2: HF formation at hot surfaces................................................................ 6

4.1 Introduction................................................................................................................... 6

4.2 Test equipment............................................................................................................. 6

4.3 Data acquisition ............................................................................................................ 7

4.4 Test procedure ............................................................................................................. 8

4.5 Combustion of fluorinated hydrocarbons...................................................................... 9

4.6 Results.......................................................................................................................... 9

5 Work package 3: Ignition behaviour at hot surfaces..................................................... 12

5.1 Introduction................................................................................................................. 12

5.2 Test equipment........................................................................................................... 12

5.3 Test procedure ........................................................................................................... 13

5.4 Results........................................................................................................................ 14

6 Work package 4: Leakages to a model volume.............................................................. 15

6.1 Introduction................................................................................................................. 15

6.2 Test procedure ........................................................................................................... 16

6.3 Results........................................................................................................................ 16

7 Work package 5: Enclosed space ignition test .............................................................. 18

7.1 Introduction................................................................................................................. 18

7.2 Test procedure ........................................................................................................... 18

7.3 Results........................................................................................................................ 19

8 Work package 6: Ignition tests in a passenger compartment of a car ........................ 21

8.1 Introduction................................................................................................................. 21

8.2 Test procedure ........................................................................................................... 21

8.2.1 Ignition of the leaking stream.................................................................................. 22

8.2.2 Ignition of homogeneous HFO1234yf-air mixture in the compartment ................... 23

8.3 Results........................................................................................................................ 25

8.3.1 Ignition of the leaking stream.................................................................................. 25

8.3.2 Ignition of homogeneous HFO1234yf-air mixture in the compartment ................... 25

9 Safety evaluation............................................................................................................... 29

10 References......................................................................................................................... 31
BAM test report page 3 of 31 pages BAM-ref.: II-2318/2009 I 

1 Scope 

BAM was commissioned by the Federal Environment Agency in German (UBA) to examine the 

reaction behaviour of 2,3,3,3-Tetrafluoroprop-1-ene (HFO-1234yf) when exposed to ignition 

sources like sparks or hot surfaces. The focus of the examinations was not only to the 

determination of the flammability in different realistic scenarios and the formation of HF due to the 

hazards caused by the toxicity of HF. Therefore lab scale tests as well as tests with a car were 

carried out and are described in the following report. 

2 Safety characteristics, terms and definitions 

The safety characteristics and terms used in this report are defined as follows: 

LEL, UEL Lower and upper explosion (flammability) limit (LEL, UEL), lower and upper 

limiting value of the flammable gas concentration in a gaseous fuel/air mixture, 

at which just no more flame propagation (explosion) takes place after an 

ignition. 

Explosion range Concentration range between LEL and UEL, which is called the explosion 

range. Fuel/air mixtures within the explosion range can be ignited by an ignition 

source. 

Explosion region For a ternary gas mixture consisting of ethane, refrigerant and air the course of 

the LEL and UEL enclose the explosion region. For each refrigerant 

concentration one explosion range with LEL and UEL exists. The sum of all 

explosion ranges forms the explosion region. 

p0 Initial pressure in a closed vessel. Unit is bara (bar absolute). 

pex Explosion pressure, peak value of the pressure time curve, measured in a 

closed vessel upon deflagration of an explosive gas mixture. 

pex/p0 Explosion pressure ratio, explosion pressure divided by the initial pressure. 

T0 Initial gas temperature in the explosion vessel. 

Tex Explosion temperature, peak value of the temperature time curve, measured in 

a closed vessel upon deflagration of an explosive gas mixture. 

MIT Minimum ignition temperature, lowest temperature of the hot surface at which a 

self ignition was observed at specified test conditions. 

Self Ignition Sudden pressure and/or temperature increase in a closed vessel. 

IDT Ignition Delay Time, time period between the start of filling the test mixture into 

the explosion vessel and the observed self ignition. 

IC Ion chromatography, analysis method for the determination of the 

HF-concentration in gas samples 

MAC Mobile air conditioning system 
BAM test report page 4 of 31 pages BAM-ref.: II-2318/2009 I 

3 Work package 1: Explosion regions of ethane-refrigerant-air mixtures 

3.1 Introduction 

In a first work package the explosion region of the ternary gas system ethane-HFO1234yf-air was 

determined. The results were compared to literature values also determined in the past by BAM 

for the ternary system ethane-R134a-air. The explosion regions of the resulting mixture 

compositions in case of a leakage of HFO1234yf with small amounts of a hydrocarbon in air will 

be discussed regarding the flammability of these mixtures. 

A detailed report [1] was already sent to the customer. 

3.2 Test procedure 

The tests have been carried out according to the former German standard DIN 51649 

“Determination of explosion limits of gases and vapours” in a glass tube. Although this standard 

was replaced by the European standard EN 1839 the former German standard was applied due 

to comparability to the literature values. Furthermore studies of BAM already showed that the 

difference between the explosion regions determined according to the DIN 51649 and EN 1839 

“T” (tube method; in EN 1839 two test methods are described, one in a glass tube and one in a 

closed bomb.) is negligible for the most fuels [2]. 

Details of the test method as well as the procedure were reported in a separate test report with 

the BAM reference number BAM-Az.: II-2318/2009 [1]. The test mixtures were prepared 

separately in a 14-dm3

-sphere with a mixing device inside. After the preparation the gas mixture 

was filled to the ignition tube, which was a vertical glass tube with an inner diameter of 60 mm 

and a height of 300 mm. This glass tube is an open system due to the non-fixed lid at the top. In 

case of strong reactions the overpressure is released by lifting the lid. 

Prior to each ignition test, the tube was purged with the test mixture. The purging volume was at 

least ten times the volume of the tube. Subsequently the test mixture by-passes the glass tube 

and was supplied into the exhaust system; the inlet to the test vessel was sealed. After purging 

the ignition tube with the test mixture the gas flow was stopped. The induction spark igniter is 

fired when test mixture is quiescent (about 15 s after gas flow was stopped), and it is observed 

whether a flame detaches from the ignition source or not. 

If an ignition is observed, the amount of ethane respectively HFO1234yf in the test mixture was 

iteratively varied until no further flame detachment occurred. The step size for the variation was 

fixed to 0.2 mol-%. The test mixture with which a further flame detachment just failed was used 

to carry out further four tests. The determination was terminated when all five tests have taken 

place without flame detachment. If this was not the case, the ethane content was varied again, 

i. e. for the determination of the LEL the ethane content was reduced by one step size; for the 

UEL, it was increased by one step size. 

This procedure was carried out for different fixed amounts of HFO1234yf respectively ethane in 

order to determine the course of the lower and the upper explosion limits and therefore the 

complete explosion region of the ternary gas system. 
BAM test report page 5 of 31 pages BAM-ref.: II-2318/2009 I 

3.3 Results 

The resulting explosion region for the ternary gas system ethane-HFO1234yf-air as well as the 

one for ethane-R134a-air is shown in Fig. 1. The explosion regions are finally comparable large 

considering the whole region. But there is an important difference to the ethane-R134a-air 

mixtures which is caused by the flammability of HFO1234yf itself. The flammability of 

HFO1234yf leads to the fact that the course of the lower explosion limit of ethane hits the x-axis 

at the LEL respectively the UEL of HFO1234yf. 

0 2 4 6 8 10 12 14 16 18 20

Anteil Inertgas bzw. Kältemittel in Mol-% 

0

2

4

6

8

10

12

14

16

Anteil Ethan in Mol-%

explosion area of ethane-R134a-air

explosion area of ethane-HFO1234yf-air

explosion area

LEL of HFO1234yf UEL of HFO1234yf

ETHAN_IG_LUFT_XY_DIN51649 | 17.11.2009

Fig. 1: Explosion regions of ethane-R134a-air and ethane-HFO1234yf-air, determined at 

atmospheric pressure and a temperature of 25 °C according to DIN 51649 

The presence of hydrocarbons depends on the use of the refrigerant. In many cases there are 

hydrocarbons present e. g. oil. Oils are hydrocarbons with long C-chains which can be cracked 

at hot surfaces. Smaller molecules are formed which can also react with the refrigerant. 

Therefore the influence of hydrocarbons on the explosion region is shown by the example of 

ethane addition. 

That leads to the fact that in case of HFO1234yf leakages the probability to produce explosive 

atmospheres in presence of hydrocarbons is larger compared to R134a. 

Especially in the range of the lower explosion limit curves a number of mixtures exists, where 

HFO1234yf becomes flammable by addition of low fractions of hydrocarbons (see difference 

between the LEL curves of HFO1234yf and R134a in Fig. 1). 
BAM test report page 6 of 31 pages BAM-ref.: II-2318/2009 I 

4 Work package 2: HF formation at hot surfaces 

4.1 Introduction 

It was well known that HF is formed when fluorinated hydrocarbons are exposed to ignition 

sources and especially to hot surfaces. This effect is also mentioned for HFO1234yf in the 

Material Safety Data Sheet (MSDS) [5] from the supplier Honeywell. In Section 2 “Hazards 

Identification”, Section 5 “Fire-fighting measures” and Section 10 “Stability and Reactivity” of the 

MSDS information regarding decomposition products are given. One of these products is HF. 

In the past many discussions arose what amounts of HF can be formed when the refrigerant is 

released from the MAC. Gas sampling after realistic scenarios is not easy. Very often the 

results reflects only the HF-amount at the places where the gas samples were taken. If a model 

test is carried out discussions about the plausibility arose very often as well as doubts regarding 

the applicability. 

In this work package the HF formation was determined away from any scenario to get an 

impression about the amounts of HF which can occur in principle after exposure of defined 

HFO1234yf-air mixtures to hot surfaces. 

4.2 Test equipment 

The test equipment is shown schematically in Fig. 2. Fig. 3 shows a picture of the set-up which 

was used for the determination of the HF-concentration after defined mixtures of refrigerant-air 

have been exposed to the vessel hot surface for ten minutes. 

The equipment was installed in a fume hood and consists of a mixing vessel (V = 14 dm3

) and a 

heated explosion vessel (V = 3 dm3

). Both vessels could be evacuated, filled and vented 

separately. 

The explosion vessel was an autoclave made from stainless, creep resistant steel (German steel 

code: 1.4122; composition in units of %-w/w: C = 0.4, Si = 1, Mn = 1.5, P = 0.04, S = 0.015, Cr = 

16.5, Mo = 1, Ni  1, Fe = 78.5) with an inner diameter of 150 mm and a height of 188 mm. 

Sealing was made from graphite. All connectors for gas inlets and outlets as well as an air cooled 

pressure transducer and a 1.5-mm-NiCr/Ni-coated thermo couple were installed in the lid of the 

vessel. The explosion vessel was heated by a heating sleeve with integrated electrical 

temperature controller and insulator from the company HORST GmbH (Inner- 175 mm; length 

280 mm, 2800 W heating capacity, max. temperature 850 °C). Bottom and top of the vessel were 

insulated by mineral fibrous insulating material. This set-up guarantees temperature gradients 

< 10 K in the explosion vessel. 

Gas sampling after the tests was realized by adding two wash bottles - each of them filled with a 

defined NaOH-solution - to the vacuum pipe. The volume taken out of the test vessel was 

controlled by a volume metering device. 
BAM test report page 7 of 31 pages BAM-ref.: II-2318/2009 I 

exhaust

gas

M

PI

TIC

102

203

6 5

O2

7

4

N2

vacuum

test gas

2

PI

103

TI

204

PIR

TIR

201

101

1

3

EL.

TI

202 8

9

exhaust

gas

vacuum

1 3 dm3 explosion vessel 

2 14 dm3

 vessel with mixing device 

3 measurement chain for pressure (piezoresistive pressure transducer, measuring range 0 bara up 

to 5 bara; amplifier; A/D-converter; computer) 

4 measurement chain for temperature (1.5-mm-NiCr/Ni-coated thermo couple, amplifier; 

A/D-converter; computer) for the determination of the initial temperature and the temperature-timehistory inside the explosion vessel 

5 Heating device with integrated controller 

6 vacuum indication 

7 piezoresistive pressure transducer, measuring range 0 bara up to 5 bara for the mixture 

preparation 

8 1.5-mm-NiCr/Ni-coated thermo couple with digital indicator 

9 Heating device with temperature controller for heating the gas inlet pipe 

Fig. 2: Schematically view of the set-up for the determination of HF after exposure of 

refrigerant-air-mixtures to hot surfaces 

4.3 Data acquisition 

In order to determine partial pressures during the mixture preparation, the initial pressures and 

the pressure-time-histories in the test vessel piezoresistive pressure transducers from the 

company Keller (explosion and mixing vessel: type PAA-10, measuring range 0 bara up to 5 

bara; both pressure transducers with a limiting frequency f > 30 kHz) were used. The 

transducers had a resolution of 0.0002 bara with a linearity better than 0.5 %. All pressure 

transducer were calibrated over the complete measuring range by means of a digital pressure 

controller DPI 515 from the company Druck (uncertainty of measurement < 0.01 % full scale). 

The initial temperatures and the temperature-time-histories inside the explosion vessel were 

measured with a digital thermometer from the company Greisinger (type GTH 1200 A) with a 

1.5 mm coated thermocouple. 

The pressure recording equipment and the temperature recording equipment in the test vessel 

were connected to an A/D-converter (company Jet Systemtechnik GmbH, Typ MCL-USB, 

16 channels 12 Bit A/D, sampling frequency 500 kHz) in a computer. All pressure-time- and 

temperature-time-histories in the explosion vessel were measured and stored digitally. 
BAM test report page 8 of 31 pages BAM-ref.: II-2318/2009 I 

a) explosion vessel 

b) mixing vessel 

c) data acquisition system 

d) heating device for the explosion vessel 

e) heating device for the pipes 

f) pressure gauge for the explosion vessel 

g) pressure gauge for the mixing vessel 

h) vacuum pump 

Fig. 3: Set-up for the determination of minimum ignition temperature (MIT) of process gases at 

atmospheric and non-atmospheric conditions 

4.4 Test procedure 

Defined gas mixtures consisting of 5 mol-%. 10 mol-% and 20 mol-% of HFO1234yf respectively 

R134a in air have been prepared separately in the 14 dm3

 spherical vessel with mixing device. 

Afterwards the homogeneous mixtures were filled into the evacuated, pre-heated explosion 

vessel of 3 dm3

. For a time period of ten minutes the pressure-time- as well as the temperaturetime-histories were recorded to detect possible ignition phenomena inside the vessel. The tests 

were carried out at three different initial temperatures of 200 °C, 350 °C and 500 °C. 

After ten minutes a 500 ml gas sample was taken out of the ignition vessel in order to analyse it 

regarding HF concentration. As analysis method mainly ion chromatography was used. 

Further tests have been carried out with mixtures where 3 % oil was added to the HFO1234yf or 

R134a before mixed with air. By that procedure the influence of oil on the HF formation could be 

detected at these specified conditions. 

a) 

g) f) 

e) 

c) 

b) 

h) 

d) 
BAM test report page 9 of 31 pages BAM-ref.: II-2318/2009 I 

4.5 Combustion of fluorinated hydrocarbons 

During the combustion of a fluorinated hydrocarbons like HFO1234yf the formation of HF is 

possible according to: 

CH2 = CF-CF3 + 2.5 O2  2 HF + 0.5 CF4 + 2.5 CO2 

Of course further products can occur like COF2 (carbonyl fluoride) which is also highly toxic. 

How much HF is finally formed is dependent on many factors influencing the pathway of 

reaction, e. g. is there a flame propagation (explosion) in the system, is pure refrigerant 

released and got in contact to a hot surface etc. The amount of the refrigerant which is 

heated up to high temperatures, like they can occur in flames, is influencing the amount of 

HF. In case of an explosion usually a flame propagates through that volume in which a 

flammable mixture is available. Therefore the HF amount found after those “explosions” are 

in the range of percentages according to the above mentioned reaction. The maximum 

amount of HF is 13.9 mol-% for a stochiometric reaction according to the formula: 

1 mol HFO1234yf + 11.9 mol air  2 mol HF + 0.5 mol CF4 + 2.5 mol CO2 + 9.4 mol N2 

This theoretical value will not be reached in most of the cases because a flame propagation 

through a complete volume is not often observed. In case the refrigerant is released usually not 

the full amount of the released substance gets into contact to hot surfaces or open flames e. g. 

the flame of a match. Nevertheless high amounts of HF can never be excluded. 

4.6 Results 

The explosions and the HF concentrations determined for HFO1234yf-air mixtures without and 

with oil are summarized in Tab. 1, for R134a-air mixtures without and with oil in Tab. 2. 

Tab. 1: HF concentrations of HFO1234yf-air mixtures after exposure to hot surfaces for a time 

period of ten minutes 

Mixture composition 

Test no. [mol-%] 

HFO1234yf air 

Vessel 

temperature 

[°C] 

Explosion 

yes / no 

HF concentration 

[mol-% ± 0.01 mol-%] ** 

UBA 04 5.0 95.0 200 no 0.01 

UBA 05 10.0 90.0 200 no 0.01 

UBA 06 20.0 80.0 200 no 0.01 

UBA 07 5.0 95.0 350 no 2.04 

UBA 08 10.0 90.0 350 yes 15.9 

UBA 09 20.0 80.0 350 yes 45.9 

UBA 16 5.0 95.0 500 no 0.71 

UBA 17 10.0 90.0 500 yes 5.58 

UBA 18 20.0 80.0 500 yes 6.90 

UBA 26 5.0 * 95.0 350 no 1.74 

UBA 27 10.0 * 90.0 350 no 1.07 

UBA 28 20.0 * 80.0 350 no 0.11 

UBA 30 5.0 * 95.0 500 no 0.62 

UBA 31 10.0 * 90.0 500 yes 1.81 

UBA 32 20.0 * 80.0 500 yes 7.27 

* mixture of 97 % HFO1234yf and 3 % oil 

** 1.0 mol-% = 10,000 ppm 
BAM test report page 10 of 31 pages BAM-ref.: II-2318/2009 I 

Tab. 2: HF concentrations of R134a-air mixtures after exposure to hot surfaces for a time 

period of ten minutes 

Mixture composition 

Test no. [mol-%] 

R134a air 

Vessel 

temperature 

[°C] 

Explosion 

yes / no 

HF concentration 

[mol-% ± 0.01 mol-%] ** 

UBA 01 5.0 95.0 200 no 0.03 

UBA 02 10.0 90.0 200 no 0.01 

UBA 03 20.0 80.0 200 no 0.01 

UBA 10 5.0 95.0 350 no 0.24 

UBA 11 10.0 90.0 350 no 0.60 

UBA 12 20.0 80.0 350 yes 12.07 

UBA 13 5.0 95.0 500 no 0.36 

UBA 14 10.0 90.0 500 no 0.21 

UBA 15 20.0 80.0 500 no 0.33 

UBA 20 5.0 * 95.0 350 no 0.03 

UBA 21 10.0 * 90.0 350 no 0.04 

UBA 22 20.0 * 80.0 350 yes 5.35 

UBA 33 5.0 * 95.0 500 no 0.15 

UBA 24 10.0 * 90.0 500 no 0.28 

UBA 25 20.0 * 80.0 500 no 0.61 

* mixture of 97 % R134a and 3 % oil 

** 1.0 mol-% = 10,000 ppm 

It turned out that high amounts of HF were detected at temperature of 350 °C and 500 °C after 

exposing the defined mixtures to a hot surface for a time period of ten minutes. The higher the 

amount of refrigerant was in the mixture the higher the amount of HF detected. In some cases 

the analysed HF concentrations were higher than those occurring for the stochiometric 

combustion reaction. Such high fractions are possible by fuel rich combustion and forming of 

COF2, which can hydrolyse with water to HF during the analysis process. Small amounts of oil 

in the mixtures decrease the amount of HF, but nevertheless several percent of HF were 

analyzed. 

At various test conditions ignition phenomena were observed. In this test series it was not the 

intention to determine these phenomena in detail, but familiar behaviour is already known for 

other hydrocarbons [6]. In Fig. 4 to Fig. 6 pressure-time- and temperature-time-histories are 

shown as example for these ignition phenomena. 

In test no. UBA 08 (10 mol% HFO1234yf in air at 350°C, Fig. 4) and in test no. UBA 09 

(20 mol% HFO1234yf in air at 350°C, Fig. 5) clear explosions were detected visible as short 

pressure and temperature peaks. The difference is to find in the ignition delay time (IDT) which 

decreased with increasing amount of HFO1234yf in the mixture. In test no. UBA 12 (20 mol% 

R134af in air at 350°C, Fig. 6) also a pressure and temperature increase was observed. It was 

also defined as “explosion” although it is an exothermic reaction not that fast as detected in the 

two tests with HFO1234yf shown in Fig. 4 and Fig. 5. In all three tests very high amounts in the 

range of percentages of HF have been analyzed. 
BAM test report page 11 of 31 pages BAM-ref.: II-2318/2009 I 

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350

time [s]

presure [bar absolut]

0

50

100

150

200

250

300

350

400

450

500

temperature [°C]

pressure-time-history

temperature-time-history

Fig. 4: Pressure-time- and temperature-time-histories of test no. UBA 08 

(10 mol-% HFO1234yf in air at 350 °C initial temperature) 

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350

time [s]

pressure [bar absolute]

0

50

100

150

200

250

300

350

400

450

500

temperature [°C]

pressure-time-history

temperature-time-history

Fig. 5: Pressure-time- and temperature-time-histories of test no. UBA 09 

(20 mol-% HFO1234yf in air at 350 °C initial temperature) 
BAM test report page 12 of 31 pages BAM-ref.: II-2318/2009 I 

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350

time [s]

pressure [bar absolute]

0

50

100

150

200

250

300

350

400

450

500

temperature [°C]

pressure-time-history

temperature-time-history

Fig. 6: Pressure-time- and temperature-time-histories of test no. UBA 12 

(20 mol-% R134a in air at 350 °C initial temperature) 

5 Work package 3: Ignition behaviour at hot surfaces 

5.1 Introduction 

The tests in work package 2 (chapter 4) were carried out without any scenario in the 

background. Maximum amounts of HF were determined after exposing specified mixtures from 

HFO1234yf in air respectively R134a in air to a pre-heated vessel. 

A real scenario in a car would be that a part of the MAC is leaky or ruptured and the refrigerant 

is released to the motor compartment. Hot surfaces are always available as far as the car was 

moving. On the one hand the ignition behaviour of HFO1234yf and R134a was examined. 

Although the minimum ignition temperature (MIT) of HFO1234yf is well known (MIT = 405 °C 

[5]) no information exists about possible ignition of the refrigerant in a flowing state. The 

minimum ignition temperature is always determined according to standards like EN 14522 [7] 

where inhomogeneous and quiescent mixtures are examined. The only forced flow is slow 

buoyancy. 

On the other hand the amounts of HF after the release and the contact to a hot surface was of 

great interest as not the complete released substance got in contact the hot metal surface. 

5.2 Test equipment 

For this test series a model volume of 200 dm3

 was constructed. One side of this box was made 

from Plexiglas®(Fig. 7). A metal block was pre-heated in a ceramic oven up to temperatures of 

1100 °C. After the block was taken out it was installed on a mesh wire to protect the walls of the 

volume against the high temperatures. The temperature of the metal block was determined in a 

small hole with a diameter of 2 mm and 2 mm depth. The temperature measurement itself was 

realized by use of a digital thermometer from the company Greisinger (type GTH 1200 A) with a 

1.5 mm coated thermocouple. 
BAM test report page 13 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 7: Model volume for release of refrigerants to a hot metal surface 

The release of refrigerant was performed by use of a 1⁄4`` pipe with a reduction to 2 mm 

diameter at its end. The released mass of refrigerant was determined with a balance from the 

company Sartorius (type 3808 MP, measuring range up to 30,000 g, resolution: 1 g). 

In a few tests the amounts of HF in the model volume were determined by use of detector tube 

of the company Dräger (type Hydrogen fluoride 0.5/a, measuring range 0.5 to 15 ppm 

respectively 10 to 90 ppm). Gas sampling was done after the release test by lifting the lid of the 

volume slightly and applying the measuring system manually. 

Data acquisition for ignition behaviour and temperature observation was realized by video 

recording. The weight of released refrigerant was noted and the amount of HF was detected by 

the detector tubes. 

5.3 Test procedure 

The pre-heated metal block was taken out from the oven and installed on the mesh wire. When 

the surface temperature dropped down to the initial temperature approximately 50 g/min of pure 

HFO1234yf or R134a were released and directed towards the metal block. Possible reactions 

were documented by video. Further tests have been carried out with mixtures where 3 % oil 

was added to the refrigerants. 

After two tests gas samples were taken as already described in chapter 4.2 in order to 

determine the HF amount by IC. In four other tests the HF amount was determined with the 

detector tubes. 

temperature measurement 

release pipe  2 mm 
BAM test report page 14 of 31 pages BAM-ref.: II-2318/2009 I 

5.4 Results 

In Tab. 3 the results of the tests regarding the ignition behaviour at hot surfaces are 

summarized. 

Tab. 3: Results/observations during leakages of R134a and HFO1234yf to a model volume 

with a hot metal surface 

Test no. Refrigerant and 

released mass 

Temperature of 

metal [°C] 

Explosion 

yes / no 

HF concentration 

[ppm] 

Box 01 R134a; 56 g 700 no no analysis 

Box 02 R134a; 53 g 800 no no analysis 

Box 03 R134a;52 g 900 no no analysis 

Box 04 HFO1234yf; 54 g 900 yes no analysis 

Box 05 HFO1234yf; 52 g 800 no no analysis 

Box 06 HFO1234yf; 55 g 700 no no analysis 

Box 07 HFO1234yf; 54 g 500 no 700 (0.07 mol-%) 

Box 08 HFO1234yf; 52 g * 500 no 500 (0.05 mol-%) 

Box 09 HFO1234yf; 51 g * 600 yes no analysis 

Box 10 R134a;52 g 500 no 0.5 *** 

Box 11 HFO1234yf; 50 g 500 no 5.0 *** 

Box 12 R134a; 51 g * 500 no > 90 *** 

Box 13 HFO1234yf; 50 g * 500 no > 90 *** 

Box 14 R134a;52 g * 600 no no analysis 

Box 15 R134a;51 g * 700 no no analysis 

Box 16 R134a;51 g * 800 no **** no analysis 

Box 17 R134a;50 g * 900 no **** no analysis 

* mixture of refrigerant and 3 % oil 

** 1.0 mol-% = 10,000 ppm 

*** detector tube 

**** small flame on hot surface due to oil 

In this test for HFO1234yf a minimum temperature for ignition was determined at 900 °C (pure 

substance, test no. Box 04, Fig. 8) respectively 600 °C (refrigerant + 3 % oil, test no. Box 09, 

Fig. 9). In both test a blue flame propagation was visible. In the test where the mixture with oil 

was released a white fog was produced at first. In this step the hydrocarbons in the oil were 

cracked and the intermediately formed species led to a lower ignition temperature than 

determined for the pure HFO1234yf. For R134a at temperatures up to 900 °C no ignition were 

observed (pure substance as well as for mixture with 3 % oil). 

The gas samples taken after test no. Box 07 and 08 were analyzed by IC for HF. In order to 

compare these values to those achieved in work package 2 (chapter 4.6) the tests were carried 

out at temperatures of 500 °C. HF concentrations determined in these tests in work package 3 

were lower compared to those in work package 2 due to lower contact times of the HFO1234yf 

to the hot surface. 

Further analysis were carried out with the detector tubes (test no. Box 10 to 13). The initial 

temperature of the metal block was always set to 500 °C. At first repetition tests with the pure 

substances were carried out to get a reference to the more precise analysis by IC. It turned out 

that the HF analysis with detector tubes (test no. Box 10 and 11) is not that sensitive as IC. The 

HF amounts were below the values determined by IC. Nevertheless in test no. Box 12 and 

13 HF amounts of more than 90 ppm were detected, when the refrigerants were mixed with low 

amounts of oil. 
BAM test report page 15 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 8: Picture sequence from the video record of test no. Box 04: Release of pure HFO1234yf 

on a hot metal surface with 900 °C initial temperature 

Fig. 9: Picture sequence from the video record of test no. Box 09: Release of HFO1234yf with 

3 % oil on a hot metal surface with 600 °C initial temperature 

6 Work package 4: Leakages to a model volume 

6.1 Introduction 

Chapter 5 described a scenario where high pressure leakages from a MAC were released and 

got in contact to a hot surface, e. g. a motor. Another scenario are small leakages, as they can 

occur e. g. from gas cylinders filled with refrigerant at a storage place. The densities of the 

refrigerants (HFO1234yf, R134a and CO2) are bigger than the density of air. Therefore the 

substances “drop down” and accumulate at the bottom. The boundary of the refrigerant layer 

can get higher the longer the release takes place. Finally the height of the refrigerant can reach 

an ignition source, e. g. a burning candle. In this work package the ignition behaviour was 

looked at when HFO1234yf as well as R134a and CO2 were slightly released into a model 

volume of 200 dm3

. 
BAM test report page 16 of 31 pages BAM-ref.: II-2318/2009 I 

6.2 Test procedure 

The same test box as described in chapter 5 was used. The mesh wire was removed and a 

candle was located in one edge of the volume (Fig. 10). Leakages with two different mass flows 

were generated. In a first test series the 1⁄4`` pipe was extended with another pipe to direct the 

release to the bottom of the box. The released mass was determined with a balance from the 

company Sartorius (type 3808 MP, measuring range up to 30,000 g, resolution: 1 g). 

Approximately 50 g of the refrigerants were released. In a second test series this inner pipe was 

also removed and the mass flow reduced so that the flow directly “dropped down” to the bottom. 

The two test series were carried out with CO2, R134a and HFO1234yf. All tests were recorded 

with a camcorder. 

Fig. 10: Set-up for the refrigerant release to a volume of 200 dm3

. 

After the tests with the fluorinated hydrocarbons the HF amount was determined by use of the 

detector tubes of the company Dräger (type Hydrogen fluoride 0.5/a, measuring range 0.5 to 

15 ppm respectively 10 to 90 ppm). 

6.3 Results 

The tests are summarized in Tab. 4. 

In the first test series (test no. V 01 to V03), the mass flows of the refrigerants were even high 

enough to cause slight turbulences during the release. In combination with that turbulences the 

flame was extinguished when the boundary layer reached the candle flame. During the release 

of the fluorinated hydrocarbons R134a and HFO1234yf a flame stretch was observed after 30 s. 

For R134a the flame size remained constant for the duration of the test. Due to the nonflammability of R134a the flame was finally extinguished after 70 s. The same test with 

HFO1234yf led also to a flame stretch, but the flame size increased all the time (Fig. 11), but no 

flame propagation through the volume was observed. Finally the flame was extinguished after 

70 s presumably due to lack of oxygen in the volume. 

In a second test series (test no. V 04 to V06), the mass flow of the released refrigerants was 

reduced. In principle, the same observations were made. For R134a and HFO1234yf at first a 

flame stretch was observed after a certain time period. Finally the candle flame was always 

extinguished, but in case of the HFO1234yf release it took 18 min. In case of CO2 and R134a 

the flame was extinguished after 360 s respectively 350 s. 
BAM test report page 17 of 31 pages BAM-ref.: II-2318/2009 I 

Tab. 4: Release of refrigerants to a 200 dm3

 box with a burning candle at the bottom 

Test no. Refrigerant and 

released mass Observation HF concentration 

[ppm] 

V 01 CO2 

(mass not determined) * Flame extinguished after 50 s no analysis 

V 02 R134a; 52 g * 

Flame got a bit larger after 

30 s, but was extinguished 

after 70 s. 

> 90 

V 03 HFO1234yf, 46 g * 

Blue flame at the top of the 

candle flame after 30 s. This 

flame got larger the more 

refrigerant was released. 

Flame extinction after 70 s (Fig. 

11). 

> 90 

V 04 HFO1234yf 

(mass not determined) 

Blue flame at the top of the 

candle flame after 500 s. Max. 

height of the blue flame during 

test was approx. 10 cm 

(Fig. 12).Flame extinguished 

after 18 min. 

> 90 

V 05 R134a 

(mass not determined) 

Flame got a bit larger after 

120 s, but was extinguished 

after 350 s. 

> 90 

V 06 CO2 

(mass not determined) Flame extinguished after 360 s. no analysis 

* Release of refrigerant for approximately 60 s. 

Fig. 11: Picture sequence from the video record of test no. V 03: Release of 46 g HFO1234yf 

within 70 s. 
BAM test report page 18 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 12: Picture from the blue stagnant flame taken after 300 s from test no. V 04: release of 

HFO1234yf 

7 Work package 5: Enclosed space ignition test 

7.1 Introduction 

The enclosed space ignition test is part of the classification procedure for aerosol dispenser. It 

is defined in Section 31 of the UN Recommendations on the Transport of Dangerous Goods – 

Manual of Tests and Criteria [8]. In the enclosed space ignition test the flammability of aerosols 

is determined when they are released from the dispenser. The flammability is strongly 

dependent on the mass of the substance released to the air and this is dependend of the inside 

pressure of the dispenser as well as of the size of the aerosol droplets which are determined by 

specific parts of the dispenser. 

Although there exist these dependencies the tests can give a very good impression of the 

flammability of substances when released as aerosol. This is possible when the refrigerants are 

released at higher pressures e. g. in MAC. Therefore the enclosed space ignition tests as 

defined in the UN Recommendations was carried out with HFO1234yf and R134a and for their 

mixtures with a compressor oil. 

7.2 Test procedure 

The test substance was released into an enclosed space with a defined geometry (inner 

volume: 200 dm3

, Fig. 13). Inside this volume a candle was located in the center in order to 

ignite the resulting aerosol-air mixtures (Fig. 14). The time period of observation was limited to 

60 s. The candle flame and the possible ignitions were recorded with a camcorder through a 

window of the volume. After each test the volume was intensively flushed with pressurized air. 

Two test series were carried out. In the first test series the mass flows of pure HFO1234yf and 

R134a as well as their mixtures with 3% oil were limited to a release of approximately 50 g in 

60 s. In a second test series pure HFO1234yf was taken out of the cylinder from the gas phase 

and from the liquid phase and the mass flow realized by the full vapour pressure inside the 

cylinder, was not limited. 
BAM test report page 19 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 13: Schematic view of the enclosed space for aerosol testing 

Fig. 14: Pictures of the set-up for the enclosed space ignition test (left picture: full view of 

enclosed space with open lid for pressure release; right picture: burning candle as 

ignition source) 

7.3 Results 

Tab. 5 summarizes the enclosed space ignition tests carried out with the fluorinated 

hydrocarbons HFO1234yf and R134a respectively their mixtures with 3 % oil. 

During the test ESI 01 to ESI 04 with R134a no special observations were made (Tab. 5). 

he test with HFO1234yf was carried out with flow limitation. It turned out that The released 

amount of HFO1234yf during the test period of 60 s was to small to lead to an ignition. The 

typical flame stretch combined with a pale blue flame was observed. This confirmed again the 

test results reported in chapter 6.3 (Leckage to a test volume). 

In tests with HFO1234yf ESI 09 and ESI 11 no flow limitation was used, so that the vapour 

pressure inside the storage cylinder led to higher release rates of the HFO1234yf. In test ESI 09 

at first the substance was released from the gas phase of the cylinder. After 50 s an ignition was 

observed (Fig. 15). In test ESI 09 only the window view was recorded. Test ESI 09 was 

repeated (ESI 10) to report a complete view of the set-up. In this test ESI 10 it is visible that due 

to the explosion pressure the right lid opened (Fig. 16). Ignition always started with a stretch of 

the candle flame followed by pale blue flames propagating upwards due to buoyancy. When this 

flame was large enough ignition of the mixture at the top started. 

100 mm

200 mm
BAM test report page 20 of 31 pages BAM-ref.: II-2318/2009 I 

Tab. 5: Enclosed space ignition tests carried out with HFO1234yf and R134a 

Test no. Refrigerant, aggregate state and 

released mass Observation 

ESI 01 R134a, gas phase, 56 g No visible reaction 

ESI 02 R134a, liquid phase, 50 g No visible reaction 

ESI 03 R134a + 3% oil, gas phase, 47 g No visible reaction 

ESI 04 R134a + 3% oil, liquid phase, 51 g No visible reaction 

ESI 05 HFO1234yf + 3% oil; gas phase; 55 g Flame stretch, blue coloured 

ESI 06 HFO1234yf + 3% oil; liquid phase; 52 g Flame stretch, blue coloured 

ESI 07 HFO1234yf; gas phase; 52 g Flame stretch, blue coloured 

ESI 08 HFO1234yf; liquid phase; 54 g Flame stretch, blue coloured 

ESI 09 HFO1234yf, gas phase, no flow limitation Ignition after 50 s 

ESI 10 HFO1234yf, gas phase, no flow limitation 

(repetition of ESI 09) Ignition after 50 s 

ESI 11 HFO1234yf, liquid phase, no flow limitation Ignition after 15 s 

Fig. 15: Picture sequence from the video record of test no. ESI 09 (window view, release of 

HFO1234yf from the gas phase, no refrigerants flow limitation). Ignition was observed 

after 50 s. 

Fig. 16: Picture sequence from the video record of test no. ESI 10 (view of complete set-up, 

release of HFO1234yf from the gas phase, no refrigerants flow limitation). Ignition was 

observed after 50 s. 
BAM test report page 21 of 31 pages BAM-ref.: II-2318/2009 I 

In test no. ESI 11 HFO1234yf was taken from the liquid phase of the gas cylinder. The liquid 

was latest vaporized when it entered the enclosed space. Release of the liquid HFO1234yf at 

these conditions led to highest HFO1234yf amounts in shortest times. Therefore the ignition 

delay was also the shortest ever detected in the test. Ignition was observed already after 15 s 

(Fig. 17). 

Fig. 17: Picture sequence from the video record of test no. ESI 11 (release of HFO1234yf from 

the liquid phase, no refrigerants flow limitation). Ignition was observed after 15 s. 

8 Work package 6: Ignition tests in a passenger compartment of a car 

8.1 Introduction 

In chapters 3 to 7 described tests in which the explosion region of HFO1234yf (chapter 3) and 

the HF formation were determined in principle (chapter 4) or different release scenarios were reenacted (chapters 5 to 7). Actually the use of HFO1234yf in MAC of cars is discussed. 

Therefore further tests were carried out in order to demonstrate the applicability of the main 

achievements of the already carried out model tests. 

8.2 Test procedure 

A commercially available car was prepared for the release of HFO1234yf through a ventilation 

slot. As location for the release or leakage into the passenger compartment the ventilation slot 

closest to the front passenger was chosen (Fig. 18). Close to this area very often the heat 

exchange device of the car ventilation and the MAC is placed. The leakage was simulated by 

the end of a 1⁄4`` pipe with a reduction part to an inner diameter of 2 mm (the same as it was 

used for tests described in chapter 5). 

Two different test series were carried out: 

 Activation of different ignition sources directly in the leakage stream and 

 Ignition of the gas phase in the passenger compartment after the complete amount of 

refrigerant was released into the compartment. 
BAM test report page 22 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 18: Leakage pipe with a reduction part (inner diameter: 2 mm) installed in the ventilation 

slot of the front passenger 

8.2.1 Ignition of the leaking stream 

For the first test series a high voltage spark ignition was installed to the neck-rest of the front 

passenger (Fig. 19, left picture). Alos, two “exploding wire igniters” (after their activation burning 

arcs between two electrodes burn) were installed close to the place where usually the head of 

the front passenger is located (Fig. 19, left picture). In a further test the high voltage spark 

igniter was modified in order to ignite a match after its activation (Fig. 19, right picture). 

Fig. 19: Location of ignition sources in order to ignite a leakage stream of HFO1234yf (left 

picture: high voltage spark and “exploding wire”; right picture: modified high voltage 

spark for the ignition of a match) 

Finally an open flame (small torch lamp operated with propane) was installed on the front 

passenger seat with an upwards directed flame (Fig. 20). The burner was operated for 

approximately 120 s. 

After each initiation of an ignition source the amount of HF in the passenger compartment was 

determined by use of detector tubes from the company Dräger (type Hydrogen fluoride 0.5/a, 

measuring range 0.5 to 15 ppm respectively 10 to 90 ppm). 
BAM test report page 23 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 20: Open flame of a small torch lamp operated with propane in order to ignite a leakage 

stream of HFO1234yf 

8.2.2 Ignition of homogeneous HFO1234yf-air mixture in the compartment 

For the second test series in the passenger compartment a more extensive data acquisition 

system was installed. Six small fans were used to homogenize the gas phase after leakage of 

900 g of HFO1234yf. 900 g was the maximum allowed mass of the refrigerant according to the 

instruction manual of the car (850 g ± 50 g). 

During the test one piezoresistive pressure transducer from the company Keller (type PAA-10, 

measuring range 0 bara up to 5 bara; limiting frequency f > 30 kHz; Fig. 21) as well as three 

thermocouples connected to digital thermometer from the company Greisinger (type GTH 1200 

A) were installed at following locations: 

 pressure transducer: between the seats of the driver and the front passenger 

 thermocouple 1: back of front passenger 

 thermocouple 2: head of driver 

 thermocouple 3: head of back passenger (right side). 

Fig. 21: View of the front passenger compartment with installed pressure transducer, fans, 

thermocouple and webcam 

webcam 

pressure 

transducer 

fans 

thermocouple 
BAM test report page 24 of 31 pages BAM-ref.: II-2318/2009 I 

In order to get information about the gas mixture composition inside the compartment before 

and after the leakage of HFO1234yf a small flexible tube was installed close to the place where 

usually the back of the front passenger is located (Fig. 22, left picture). This tube was connected 

to an oxygen analyzer from the company Servomex (type 5200 Multipurpose, measuring range 

0 to 100 vol-% O2, resolution: 0.1 vol-%). 

Three pyrotechnical igniters were used as ignition sources for this test series. They were 

modified in order to ignite matches. Each of them could be activated separately. First location 

was as well close to the place where the back of the front passenger is located (Fig. 22, left 

picture). The ignition was initiated this location at first, for here information about the gas phase 

composition was available due to the installed flexible tube. Two further igniters were installed 

at the seats of the front passenger and the right back passenger (Fig. 22). 

The density of the refrigerant is bigger than the density of air. Therefore the HFO1234yf would 

be collected at the bottom of the compartment. However, the target of this test was to ignite a 

homogeneous mixture. In order to achieve this homogeneous mixture six fan bundles to a stack 

of two were installed at three locations: on the middle top of the dashboard, between the neckrest and the seat-rest of the front passenger and below the roof of the driver (Fig. 23). 

Fig. 22: Location of the modified pyrotechnical igniters for match ignition and location of the 

O2-analysis tube 

left picture: O2-analysis tube and igniter 

middle picture: igniter at the front passenger seat 

right picture: igniter at the right back passenger seat 

Fig. 23: Location of the fans for mixture homogenization 

left picture: fans on the dashboard 

middle picture: fans between the neck-rest and the seat-rest of front passenger seat 

right picture: fan below the roof of the driver’s side 
BAM test report page 25 of 31 pages BAM-ref.: II-2318/2009 I 

8.3 Results 

8.3.1 Ignition of the leaking stream 

In all together three tests the ignition of leaking streams of 260 g (first test), 160 g (second test) 

and 320 g HFO1234yf (third test) no flame propagation or any flame phenomena comparable to 

those described in the previous chapters, e. g, chapters 5, 6 and 7, were observed. In Fig. 24 a 

picture sequence is presented where the modified high voltage spark igniter was used in order 

to ignite a match. Due to the turbulences in the leaking stream the flame was extinguished soon 

after initiation. 

Fig. 24: Picture sequence from the video record where a HFO1234yf stream was ignited by use 

of a modified high voltage spark igniter with a match 

After each test the amount of HF possibly formed during the tests were detected. A person 

wearing protective clothing took three samples by opening the doors for approximately 30 s, at 

first behind the front passenger seat, then behind the driver’s seat and finally at the driver’s 

location. When the high voltage spark, the exploding wire igniter or the match were activated, 

no amounts of HF were detected. In case of the small propane torch lamp, where the open 

flame was much larger than the flame of the match, at all locations HF amounts over 90 ppm 

were detected. 

8.3.2 Ignition of homogeneous HFO1234yf-air mixture in the compartment 

For this test 900 g HFO1234yf were released to the passenger compartment of the car. During 

the filling process the six fans operated. The amount of oxygen in the compartment was 

analyzed during the test. As long as HFO1234yf was filled into the compartment the O2-amount 

was lowered starting at 20.9 mol-%. The lowering of 0.1 mol-% O2 resulted in approximately 

0.5 mol-% HFO1234yf which were filled into the compartment. After the leakage of 900 g 

HFO1234yf into the compartment a O2-amount of 19.9 mol-% were determined at the back-seat 

of the front passenger (location of the flexible tube for the O2-analysis). Therefore the O2-

amount was reduced by 1 mol-%, so that finally approximately 5 mol-% HFO1234yf were filled 

into the compartment. 

Before the first ignition was initiated the fans were switched off in order to avoid turbulences 

during the ignition which could influence a possible flame propagation. No “explosion” or flame 

propagation could be observed. The match burned and ignited the flexible tube located close to 

the ignition source. The test was recorded with two camcorder and the webcam. Picture 

sequences are presented in Fig. 25 and Fig. 27. 

The seat of the front passenger started burning 25 s after ignition, at first the back-rest and 

afterwards the neck-rest. 50 s after ignition smoke development was observed. The smoke was 

collected below the roof. More important was the fact that at this time the windows got 

translucent from the inner side like milk glass. This was caused by the HF corrosion, which was 

first observed at the back window (Fig. 25, second row). 
BAM test report page 26 of 31 pages BAM-ref.: II-2318/2009 I 

After 70 s an extreme smoke development was observed, attended with combustions especially 

in the back-room of the compartment. Smoke development stopped suddenly after 90 s. We 

supposed flame extinguishment at this moment. The O2-analysis still operated. At this moment 

the amount of O2 was only 10 to 11 mol-% and therefore too small to support a combustion. 230 

s after the ignition was initiated the door was opened by use of a wire fixed to the handgrip of 

the front passenger door. No combustion was observed, only extensive yellow smoke got out of 

the compartment. 

Fig. 25: Picture sequence from the video record of the ignition inside the passenger 

compartment. 

Two pictures of the sequence presented in Fig. 25 were enhanced in order to show the 

corrosion of the window glasses in more detail. This corrosion was caused by the HF formed 

quickly after the combustion started in the compartment. The pictures were taken 50 s 

respectively 52 s after ignition. 
BAM test report page 27 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 26: Enhancement of two pictures shown in Fig. 25 (first two pictures of the second row) in 

order to demonstrate the translucent glass as a matter of the HF corrosion 50 s resp. 

52 s after the ignition started. 

Another view of the test was given by the video record of the webcam (Fig. 27). Unfortunately 

the fixation became a bit loose, therefore ignition was only visible at the upper right side of the 

pictures. Nevertheless the start of the burning tube of the O2-analysis could be seen as well as 

burning pieces from the roof fall down. The extreme smoke development after 70 s as well as 

the final flame after 90 s was recorded. 

Fig. 27: Picture sequence from the webcam record inside the passenger compartment taken 

during the ignition. 
BAM test report page 28 of 31 pages BAM-ref.: II-2318/2009 I 

During ignition further data were recorded in order to get as much information as possible 

during the test. Due to the fact that no explosion was observed no pressure peak was 

determined inside the compartment. Therefore the most important data were the temperaturetime-histories recorded at different locations inside the compartment. The histories are 

presented in Fig. 28. The time scale differs from the above mentioned scaling, because the data 

acquisition started during the time period where the HFO1234yf was introduced to the 

compartment. Ignition was initiated after approximately 100 s after the start of the introduction of 

HFO1234yf to the compartment. 

Due to the combustion development inside the passenger compartment the temperatures 

increased to a max. of 585 °C (location: head of front passenger) respectively 555 °C (location: 

head of driver) and 358 °C (location: head of back passenger). The max. temperature values at 

the different locations were reached after different times and validate the supposed combustion 

development inside the compartment. 

Fig. 28: Temperature-time-histories of the three thermocouple installed to the passenger 

compartment. 

Fig. 29 presents pictures after the test. Beside the typical view of a combustion inside the 

passenger compartment of a car the translucent glasses caused by HF corrosion were most 

impressive. Such corrosion effects were initiated at high HF amounts which were supposed to 

be much higher than 90 ppm and already occurred 50 s after the combustion started. The HF 

amount was not validated by measurements. 

ignition 
BAM test report page 29 of 31 pages BAM-ref.: II-2318/2009 I 

Fig. 29: Pictures taken after the combustion in the passenger compartment. Beside the typical 

view of such an event the translucent glasses caused by HF corrosion are impressive. 

9 Safety evaluation 

BAM was commissioned by the German Federal Environment Agency (UBA) to examine the 

reaction behaviour of 2,3,3,3-Tetrafluoroprop-1-ene (HFO-1234yf) when exposed to ignition 

sources like spark ignition or hot surfaces. It was published by different authors that this 

substance will be used as new refrigerant in MAC of cars as it has a much lower global warming 

potential than the actual refrigerant R134a. But the new refrigerant is a flammable gas. 

According to the Globally Harmonized System (GHS) HFO1234yf is classified as “extremely 

flammable” as it has a lower flammability below 13 mol-% [5]. Consequently, different institutes 

worldwide started examinations in order to determine potential hazards using HFO1234yf in 

MAC. The assessment of the hazards presented by a substance in normal use in technical 

equipment cannot take place based on only a single individual test series. Various systematic 

scenarios ("incidents") must be analysed and a holistic hazard analysis performed. Only then it 

is possible to comment reliably on the dangers posed by the use of such a substance in 

technical devices. 

Therefore several studies were carried out and presented in this test report in order to examine 

some incidents and to determine possible hazards resulting from the exchange of the actual 

refrigerant R134a. The focus of all examinations was not only the determination of the 

flammability in different realistic scenarios. Also the formation of HF was of great interest due to 

hazards caused by the toxicity of HF. In this tests for UBA, lab scale tests as well as tests with a 

car have been carried out. 
BAM test report page 30 of 31 pages BAM-ref.: II-2318/2009 I 

The main conclusions of all examinations presented in chapters 3 to 8 can be summarized as 

follows: 

 The refrigerant HFO1234yf is not that easy to ignite as substances like propane or petrol 

vapours. Furthermore the LEL is higher compared to those substances. 

 Ignition behaviour - when HFO1234yf is exposed to ignition sources like spark ignition 

etc. - is to describe as unpredictable and is strongly dependent on the circumstances at 

which the refrigerant is released and on the flammable mixtures with air occuring. 

 Below the LEL concentration of about 6 mol-% HFO 1234yf no self sustaining flame 

propagations could be observed, but extreme stretches of typical blue flames. 

 Once a flame stretch was observed parts of the flame were detached. These flames can 

lead to fires dependent on the surrounding of the flame detachments. 

 The minimum ignition temperature of HFO1234yf is 405 °C. This is defined as the lowest 

temperature at which an ignition can occur when the most ignitable mixture is present. In 

release scenarios higher surface temperatures are needed for an ignition. This 

temperature can be decreased if other flammable substances are present, e. g. petrol in 

cars. 

 Regarding fire and explosion hazards it can be pointed out that in a car, in addition to 

the air conditioning system refrigerant, many other substances like fuels and materials 

are used, which – depending upon the scenario – can also lead to hazards to humans 

and the environment. The additional hazard regarding fire and explosion caused by the 

HFO1234yf is comparable low compared to all other fuels and materials. 

 Critical is the formation of hazardous amounts of HF when HFO1234yf is exposed to 

ignition sources like open flames and hot surfaces. In nearly all tests where the 

refrigerant was released at specified test conditions the detected HF amounts exceeded 

critical amounts for humans health. According to the “Acute Exposure Guideline Levels 

(AEGL) these amounts are that high that after 10 min exposure irreversible damages to 

somebody’s health can occur. In Tab. 6 the AEGL values for HF published by the USNational research council and the National Academy of Sciences are presented [9]. 

 The tests were carried out in comparison to R134a, the actual refrigerant in MAC. This 

refrigerant is non-flammable at atmospheric conditions. Nevertheless at elevated 

conditions of temperature and/or pressure or the presence of other fuels it can ignite. 

 R134a is a fluorinated hydrocarbon which can also form HF when exposed to ignition 

sources. Nevertheless it is not that reactive as HFO1234yf so that the hazards regarding 

HF formation is evaluated to be lower for 134a than for the HFO1234yf. 

Tab. 6: AEGL values for Hydrogen fluoride (ppm) [9] 

time of exposure 10 min 30 min 60 min 4 h 8 h 

AEGL 1 [ppm] 1.0 1.0 1.0 1.0 1.0 

AEGL 2 (irreversible damages 

to humans health) [ppm] 

95.0 34.0 24.0 12.0 12.0 

AEGL 3 (life-threatening or lethal) [ppm] 170.0 62.0 44.0 22.0 22.0 

Finally it can be summarized that in case of HFO1234yf usage a careful holistic hazard analysis 

has to be performed. Many precautions will have to be defined to assure that the hazards are 

ethical and justifiable according to the actual state of technology.