Safety research of A2L/A3 refrigerants andrisk assessment in Japan
Eiji Hihara
The University of Tokyo1

Trade-off relationship between GWP andflammability••To reduce the emission of greenhouse gases including HFCs fromrefrigerating and air-conditioning equipment, a change in refrigerants from
HFCs to lower GWP refrigerants is one of the key issues.
R1234yf, R32, and R290 have much lower GWPs than R410A. R410A isnonflammable, but R1234yf, R32, and R290 are flammable. Because theburning velocities of R1234yf and R32 are smaller than 10 cm/s,
flammability of R1234yf and R32 is mild and it is categorized under the A2Lclass of the ASHRAE.
Refrigerant

R410A

R32R1234yf

R717

R290

Boiling temperature, ºC

-51.4

-51.7

-29.4

-33.3

-42.1

Critical temperature, ºC

71.3

78.1

94.7

132.4

96.7

GWP (100 years)

2088

675

4

<1

<3

Burning velocity (cm/s)

-

6.7

1.5

7.2

38.7

LFL [vol %]

-

13.3

6.2

15

1.8

UFL [vol %]Minimum ignition energy(mJ)
Flammability

-

29.3

12.3

28

9.5

-15500210.246

12L2L2L

32Research committee on risk assessment ofA2L/A3 refrigerants in JSRAE• For promoting the use of low-GWP refrigerants, relaxation of the legal
regulation of mildly flammable refrigerants is necessary. Before
relaxing regulations, risk assessment of flammable refrigerants should
be carried out, and reasonable guidelines for safe design and safe useof refrigerating and air-conditioning equipment with flammable
refrigerants should be formulated.
• A project sponsored by the New Energy and Industrial TechnologyDevelopment Organization (NEDO) on the performance and safety ofnew refrigerants started in 2011. The Japanese Refrigeration and Air
Conditioning Industry Association (JRAIA) also started the risk
assessment of flammable refrigerants. To exchange knowledge ofsafety issues and risk assessments among researchers andmanufacturers, a research committee was established by the Japan
Society of Refrigerating and Air Conditioning Engineers (JSRAE).
3

Organization of the research committee forsafety of A2L/A3 refrigerants
Japan Society of Refrigerating and Air Conditioning Engineers, JSRAE
Chair: Hihara
Secretary: Fujimoto
University of TokyoJapan Automobile
Manufacturers Association,JAMAJapanese Refrigeration andAir-conditioning IndustryAssociation, JRAIATokyo University of Science, Suwa
Kyushu University
National Institute of Advanced
Industrial Science and Technology,
AIST
Observers-NEDO-METI-KHK

4

Methodology of Risk Assessment[Probability of fire accident]＝[Rapid leakage] X[High concentration of refrigerant] X [Ignition source]
Concentration higher thanlower flammability limit

Existence of an ignition
sourceIgnition

Rapid leakage

5

Numerical simulation of diffusion ofrefrigerant leaking in a room

The University of Tokyo

6

Purpose
Flammable refrigerants leakage = Risk of fire accident
Risk =

Flammable gas volume,
presence time,and existence probability of ignition source

Flammable gas volume and presence time etc…
are numerically analyzed when a refrigerant leaked
into a living space• Target refrigerants– R32, R1234yf, R1234ze, R290

• Target equipments– RAC. for home, VRV, Chiller• Located– Indoor, Outdoor, Machine room7

Leakage scenarios for split air conditioners
Position of leakage

Wall-mounted
indoor unit

Floor-standing
indoor unit
Outdoor unit

No.

Refrigerant

Amount[g]

Flow rate[g/min]

1

R32

1000

250

2

R1234yf

1400

350

3R321000

125

4R1234yf

1400

175

5

R321000

1000

6R1234yf

1400

1400

7R2905001258R29020050

9R321000

250

10R1234yf

1400

350

11R321000

250

12R1234yf

1400350

Ventilation
None
None
None
None
None
0.5 m/s8

Result：Concentration distribution（No.1）
・Because the density of R32 ishigher than air, R32 flows down tothe floor, and is accumulated.
・The concentration was lower
than the LFL on the floor.

UFLLFL

Refrigerant：R32
Amount：1000 g
Flow rate：250 g/min

¼ LFL
9

Result：Combustible gas region（No.1）
・The combustible gas region
existed just below the air outletof the indoor unit only.
・The flammable gas volume
was very small.
・After leakage, the combustible
gas region vanishedin less than a second.

Refrigerant：R32
Amount：1000 g
Flow rate：250 g/min
10Result：Combustible gas region（No.1）
・The combustible gas region
existed just below the air outletof the indoor unit only.
・The flammable gas volume
Combustion
does not occur
was very small.
if the ignition
does
not exist
・Aftersource
leakage,the combustible
inside thegas
indoorregionunit.
vanished
in less than a second.

Refrigerant：R32
Amount：1000 g
Flow rate：250 g/min
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Result：Concentration distribution（No.9）
・There was a region wherethe concentration was higher
than the UFL on the floor.

Refrigerant：R32
Amount：1000 g
Flow rate：250 g/min

UFLLFL¼ LFL
12

Result： Combustible gas region（No.9）
・The mixing of the refrigerant isweak, and the refrigerant
concentration in the vicinity of thefloor is high.
・ In this case, not only thecombustible gas volume is large,
but also its duration is long.

Refrigerant：R32
Amount：1000 g
Flow rate：250 g/min
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Result： Combustible gas region（No.9）
・The mixing of the refrigerant isweak, and the refrigerant
concentration in the vicinity of thefloor is high.
・ In this case, not only thecombustible
gas volume
is large,The leakageof flammable
refrigerants
but also its duration
is long.
from a floor-standing
indoorunit hasa high risk of fire.

Refrigerant：R32
Amount：1000 g
Flow rate：250 g/min
14

Flammability of 2L refrigerants

National Institute of Advanced Industrial
Science and Technology (AIST)
Research Institute for Sustainable Chemistry15Flammability limits of non-flammable refrigerants
R-410A, R-410B, and R-134a are considered to be non-flammable.
However, they become flammable under such a condition as 50%RH at60 °C.

LFL
vol%
R22UFL±vol%±non-flammable

R134a

11.5

0.3

15.9

0.4

R410A

15.6

0.2

21.8

0.4

R410B

16.3

0.3

20.9

0.4

R413A

7.16

0.15

14.3

0.5
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Dependence of humidity on flammability limit

Flammability limit of R-32 and ammonia

15141312111098
76
5301234yf,LFL
1234yf,UFL
1234ze,LFL
1234ze,UFL

LFL, HFL, vol%LFL, HFL, vol%Flammability limit of R-1234yf and R-1234ze(E)25HFC-32,LFL
HFC-32,UFL
NH3,LFL
NH3,UFL

2015

10020406080

Relative humidity at 23°C, %100020406080

100

Relative humidity at 23°C, %Flammability limits of R-1234yf and R-1234ze(E) are clearly effected byhumidity. Flammable region is stretching by moisture.
Flammability of R-32 and ammonia is not influence by humidity.
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DC spark generator+-Acrylic cylinder
Electrodes with
100-mm ID plates
FanQuenching distance (dq), mm

Quenching distance measurement
25202L15d q = a (λav c p ρ 0 Su )1234yf2, 3717
32143a2L152a290

2, 310717

1032
5152a

143a

290

00

Micrometer

1001234yf

10203040

Burning velocity (Su0,max), cm/s

10.01

0.10

1/(ρ0Su0,max1.00), 102 m2s/kg

The quenching distance has a strong relationship with flammability,
like burning velocity.
The quenching distances of 2L class refrigerants are larger than 5mmm..

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Experimental Evaluation of PhysicalHazard of A2L Refrigerant Assuming
Actual Handling Situations
Tokyo University of Science, Suwa

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P hysical Hazard evaluation assum ing conceivable accident scenarios (TUSS)

Background & Objective

In the actual handling situation of air conditioning systems…
➣Leaked refrigerant
generally has a certain
degree of concentration
distribution.

➣Ignition source is veryvarious, and ignition
behavior greatly affected by
the turbulence and flow of
the accumulated refrigerant.

We examined physical hazard by burning of A2L refrigerant

under several conceivable accident situations
based on these fundamental combustion behaviors.

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P hysical Hazard evaluation assum ing conceivable accident scenarios (TUSS)

Use w ith fossil-fuel heating appliance

Accident scenario: A wall-mount type room air conditioner

containing an A2L refrigerant is simultaneously used with afossil-fuel heating appliance inside a general living space.
【Experiment】

2800

観測室

Stove（2.4 kW）
Fan heater (3.2kW）
400

2800
2100

Air conditioner

FTIR FTIR

BD

refrigerant

to vacuum

MonitorcylinderLoggerAmp.
Measurement position ofrefrigerant and HF concentration

Unit: mm

Refrigerants：R32, R1234yf, R410A
Leak amount：800 g
Leak rate：10 g/min, 60 g/min
Heater：radiative stove (2.4 kW), oil fan heater（3.2 kW）

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Physical Hazard evaluation assuming conceivable accident scenarios (TUSS)Heater: radiative stove
10g/min, Refrigerant
60g/min, Refrigerant
10g/min, HF
60g/min, HF

R32 Concentration (vol%)

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

AC-ON
020

40 60 80 100 120
time (min)

1000
900
800
700
600
500
400
300
200
1000

HF Concentration (ppm)【Results】

HF Concentration (ppm)

Use with fossil-fuel heating appliacne
2000
1800
1600
1400
1200
1000
800
600
400
200
010g/min, AC-OFF
10g/min, AC-ON
60g/min, AC-OFF
60g/min, AC-ONR32
R1234yf R410A
Varieties of Refrigerants➢ Refrigerant concentration (<2 vol%) was much lower than LFL.
Therefore no ignition and flame propagation to A2L refrigerants wereobserved.
➢ Hydrogen fluoride which is generated due to the combustion or
thermal decomposition was confirmed. The concentration of generated
HF is more than 3 ppm which is the permissible value, even R410A.

22

P hysical Hazard evaluation assum ing conceivable accident scenarios (TUSS)

I gnition & flam e propagation by a lighter

Accident Scenario: A service operative uses a portable lighter to smoke in aspace in which an A2L refrigerant has leaked and accumulated.

Type 1: piezo gas lighter
Refrigerant: R1234yf, R1234ze(E), R32
Pneumaticcylinder

Solenoid valve

Lighter

Extinction
Flame (1/30s passed)

300

Push rod

air1000【Experiment】

It was predicted that the concentration of n-butane/A2L
refrigerants/air mixture is within the flammable range when theconcentration of A2L refrigerants close to a gas lighter is less thanLFL.
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Conclusion
1.

2.
3.
4.

From 2011 to 2015, the Research Committee conducted safety researchand risk assessment of A2L refrigerants. A new guideline of mildly
flammable refrigerants for refrigerating and air conditioning equipment
was drafted in 2016.
New safety rules and regulations came into effect in 2016. R32, R1234yf
and R1234ze(E) can be used as inactive gases for refrigerating and airconditioning equipment.
The Research Committee started to conduct the safety research and risk
assessment of A3 refrigerants from 2016.
The final report on risk assessment of mildly flammable refrigerants canbe freely downloaded from the following website.
http://www.jsrae.or.jp/jsrae/committee/binensei/risk_eng.html

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Thank you for your attention!

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