ICR2015, Yokohama, Aug.16-22 2015

1.5

Hazard assessment of the combustion of
mildly flammable refrigerantsa*

Tei SaburiaNational Institute of Advanced Industrial Science and Technology (AIST),
Research Institute of Science for Safety and Sustainability

Acknowlegement
This study was made possible by the NEDO (New Energy and Industrial
Technology Development Organization)-sponsored project, "Development of Nonfluorinated Energy-Saving Refrigeration and Air Conditioning System" in FY2013FY2015.

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Contents list

1. Background
2. Scale eﬀect on ﬂammability
3. Explosion severity evaluation
4. Summary2

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Background•To promote A2L refrigerants effectively and safely, thosefundamental flammabilities such as flammability limits,burning velocity, and MIE, etc. have been characterized(as shown by Dr. Takizawa).

•

Hazard assessment on actual situation based on accidental
scenario is also important to estimate the levels of extent
of injury for the risk verification and the risk reduction
measures.

•We should scale up and reflect the evaluation results bylaboratory-scale standardized condition to the full-scale
physical hazard evaluation.
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Research Committee for the risks associated withmildly ﬂammable refrigerants
Project Chair:Prof. Hihara
Associate Chair:Mr. Fujimoto
University of Tokyo

JRAIA Safety Committee

Japan Refrigerating and Air
Conditioning Industry
Association (JRAIA)

Kyushu University

Japan Society ofRefrigerating and Air
Conditioning Engineers(JSRAE)

Japan Automobile
Manufacturers Association(JAMA)

Tokyo University of
Science at Suwa
National Institute ofAdvanced Industrial Scienceand Technology (AIST)

Observers:
Ministory of Economi, Tradeand Industry (METI)New Energy and Industrial
Technology Development
Organization (NEDO)High Pressure Gas Safety
Institute of Japan (KHK)
Kansai Electric Power Co., Inc.

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ICR2015, Yokohama, Aug.16-22 2015

Research Committee for the risks associated withmildly ﬂammable refrigerants
Physical Hazard Evaluation of A2L Refrigerants Based on Several
Conceivable Handling Situations
National Institute ofAdvanced Industrial Scienceand Technology (AIST)Tokyo University of
Science at Suwa

Hazard assessment of the combustion of mildly
flammable refrigerants:
Combustion and explosion assessment
Explosion hazard assessment ( scale effect )Explosion severity evaluation

Hazard assessment based on accident scenarios# 1 the concurrent use of a wall-mount type room air
conditioning system with a fossil-fuel heating system# 2 handling of A2L refrigerants at the factory for service
and maintenance.
# 3 use in the Variable Refrigerant Flow (VRF) system.

Achievement of Hazard assessment in actual scale5

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Contents list

1. Background
2. Scale eﬀect on ﬂammability
3. Explosion severity evaluation
4. Summary6

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Scale eﬀect on ﬂammability• The effects of temperature and humidity on the flammablebehaviour of A2L refrigerants have been reported (*Kondo, 2012);
this is an important issue, especially with the hot and humid climate ofJapan where over 30°C temperature and 80% humidity are often
recorded in the summer.
*Kondo, S., Takizawa, K. & Tokuhashi, K. (2012), J. Fluorine Chem., 144; 130–136.

In this study
the flammable behaviour of A2L refrigerants in thepresence of moisture and elevated temperatures was
experimentally investigated using a large volume
combustion vessel to see the scale and buoyancy effects.
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Experiments

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Experimental setup
Φ2mm

7mm

7mm gap

Φ100cm spherical combustion vessel
equipped with mantle heater jacket

discharging electrode9

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Experimental
setup
N
2

BG BG

TC

Pressure
Pressure gauge

Φ1000 mm (= 524l)
DPT

Cam
Cam
Electrode

Ａ
Ｉ
Ｒ

RP

Data LoggerDP

Bubbler
RP : Rotary pump
DP : Diaphragm pumpHigh Voltage
Cam : High-speed camera
Probe
BG : Diaphragm gauge
DPT : Dew point transducer
TC : Thermo couple

Trigger

RP

Ｆ
Ｕ
Ｅ
Ｌ

To waste gas cleaner

SignalSpherical Vessel

High-Voltage
SupplyTrigger

Pulse
Generator

Oscilloscope

SignalStrain gauge pressure sensor: KYOWA PHL-A (range: 2MPa, rate 100kS/s)High speed video camera: Photon SA-Z (1024×1024pixels @ 1000fps)

Schematic illustrate of experimental apparatus
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Experiments
Fuel/Air equivalence ratio Φ wasdetermined from previous study.
• R32 Φ=1.1 (19 vol% in air)
• R1234yf Φ=1.325 (10 vol% in air)
• R1234ze Φ=0.8-1.325 (10 vol% in air)Measurement
Premix combustion test was conductedby electric discharge using a Φ1m
spherical vessel (524L)• High speed video image observation• effect of buoyancy and viscosity on
the flame propagation and shape• Pressure measurement• peak pressure, rate of pressure rise

Experimental condition

Refrigerant

R32

Equivalenc

Temperaturee ratio (φ)(°C)

Mositure(wet-drycondition )

1

35

Dry

1.1

35

Dry

35

Wet (64% RH)

R1234yf

1.325

30

Dry



1.325

35

Wet (78% RH)

R1234ze

0.8-1.5
1.2
1.325

Dry
35

Wet(50%RH)
Wet(55%RH)

Evaluation• Flame speed, burning velocity, anddeflagration index(KG)

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High-speed video
observation
results

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The flame expanded while slowly climbing upward and the shape offlame front was distorted under the influence of buoyancy, thermal
expansion of the flame and thermal convection.

R32 30℃ dry

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High-speed video observation•

Frame fronts of A2L refrigerants were smooth andwrinkled front was not seen in large volume vessel
even under moisture and elevated temperature
conditions.

200ms

400ms

150ms
300ms
100ms

50ms

200ms

dry
wet
R32 (φ=1.0、35℃)

32℃, dry)dry(10℃) (Φ1.32,dry(35compact elongatedcylindrical
vesselyf(φ=1.325)

Large spherical vessel

wet(35℃)

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A practical index for estimating safety
KG:deflagration index* (*ISO 6184-2, NFPA68 2007)

Deflagration index for gases KG (100kPa·s-1) is described using maximum
pressure rise rate in the vessel (dP/dt)max and the volume of vessel Vvessel
as followsdP
KG =· V 1/3
dt maxP : Pressure (105 Pa)t : time (s)V : the volume of vessel (m3 )KG is used for estimating effect of deflagration in closed
space and designing explosion venting area of enclosures.
Larger KG value, larger venting area should be required forpreventing enclosure burst.
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Table of KG and other flammable parameters for typical gases
P max(100 kPa)

Acetylene

10.6 *11415 *1

Hydrogen

*1

*1

6.8

Detonation limits (%) *3

Cofined tube

166 *2

2.5—80.0 *3

4.2—50.0

305

*2

*3

18.3—58.9

400

2.70—36.0 *3

3.32—14.70

490

48 *2

1.3—7.9*3

1.6-5.55

562

Burning velocity-1(cm·s -1 )(100 kPa·m·s )
550

312

80 *2

Ethylene
Diethyl ether

Flammability
limits (%)

KG

Flammable
Material

8.1

*1

115

*1

Benzene47

4.2—75.0

Autoignition
Temperature ( )*7*2

Ethane7.8 *1106 *1

47 *2

3.0—12.4 *3

2.87—12.20

4.0–9.2

515

Propane

7.9 *1100 *146 *2

2.1—9.5*3

2.57—7.37

3.0–7.0450

Butane8.0 *1

92 *1

45 *2

1.8—8.4*3

1.98—6.18

2.5–5.2405

Ethyl alcohol

7.0 *1

78 *1

3.3—19.0 *3

5.1—9.8

Methanol

7.5 *1

75 *1

56 *2

Methane

7.1 *1

55 *1

40 *2

Ammonia

5.4 *110 *1

7.2 *415—28 *5651

*1 Ref. (NFPA68, 2007), Table E.1 (0.005 ft3 sphere; E = 10 J, normal condition).
*2 Ref. (NFPA68, 2007), Table D.1.
*3 Ref. (Mannan, 2005), Detonation limits obtained for conﬁned tube. *4 Ref. (ISO/DIS 817, 2010)*5 Ref. (NFPA325, 1994) *6 Ref. (JFMA, 2013)*7 Ref. (Mannan, 2005), Table 16.4

• The relative explosion severity of flammable gases was listed in order of KG.
• We can know the relative severity of A2L refrigerants by estimating KG.

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KG value in different volume•

KG value is compared with that measured by 15L spherical vessel.
• R32• Equivalence ratio Φ=1.0
3.0

R32 1.000, 35.0ﾟC, dry @524L

2.0

KG = 7.6 [100kPa m/s]

1.0

R32 1.0, 35.0ﾟC, dry @15L

0.0

Pressure (MPa)R32 1.000, 35.0ﾟC, dry @524L
Pmax = 0.75 [MPa]0.6

R32 1.0, 35.0ﾟC, dry @15L
Pmax = 0.59 [MPa]

0.4

400

PentanePropane200
Methane

0.2
0.0

0

5

10

15

Time (s)Pressure profile for R32 Φ1.0•

600

KG = 6.8 [100kPa m/s]

0.8•

NFPA68 Figure C.1

Hydrogen

KG (100kPa/s)

dPdt (MPa/s)

800

00.001 0.01

R32

0.1

1

10

100

1000

3

Test vessel volume (m )Effect of test volume on KG
measured in spherical vessels.

KG s are around 7-8 [100kPa•m/s]
There is no significant potential of increase in KG value at present.

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dPdt (MPa/s)

2
1
0
-1
-2
1.0

R32 φ1.1
dry at 35 °C (φ1.0)
dry at 35 °C

Pressure (MPa)0.8

wet at 25 °C
wet at 35 °C

0.6
0.4
0.2
0.0

•

0.4
0.0
R1234yf φ1.325
dry at 10 °C (φ1.0)
dry at 30 °C
dry at 35 °C
wet at 30 °C
wet at 35 °C

0.8
0.6
0.4
0.2
0.0

0

•

0.8

-0.4
1.0

Pressure (MPa)dPdt (MPa/s)

Pressure proﬁle

1

2

3

4

5

6

0

2

4

6

8

10

Time (s)Time (s)Pressure profile for R32

Pressure profile for R1234yf

R32 is not so sensitive to temperature and moisture.
R1234yf is obviously sensitive to temperature andmoisture on temporal change of pressure (dP/dt).

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0.70
0.4
0.0

R1234ze 35°C
0.8
1.0
1.1
1.2
1.325
1.4

0.6
0.5
0.4
0.3
0.2

9

0.65

8

0.60

7
0.55
R1234ze (35ºC, wet)Pmax (MPa)KG (100kPa)

0.1
Pmax = 0.65 [MPa]

0.0
0

2

4
Time (s)68

KG (100kPa/s)

0.7

Pressure (MPa)

10

0.8

Peak Pressure (MPa)dPdt (MPa/s)

Pressure proﬁle and burning velocity for ze

0.50

0.8

0.9

1.0

1.1

1.2

1.3

6

1.4

Equivalant ratio (φ)

Fig. Example proﬁles of R1234ze at 35 C and wet condition(left: eﬀect of equivalence ratio on pressure proﬁle,right: eﬀect of equivalence ratio on Pmax and KG).

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R1234ze

0.8-1.5
1.2
1.325

Dry
Wet(50%RH)
Wet(55%RH)

35

6.8
6.5

Not flammable
ICR2015,
Aug.16-22
2015
8.81 Yokohama,
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4.1
6.73
37
4.5

Comparison between other gases
Table 2 Comparison of P

, K and other parameters with other typical gases.

G
Table Comparison of Pmax, Kmax
G and other parameters with other typical gases.

Flammable Material
Acetylene
Hydrogen
PropaneMethaneAmmonia
R32†
R1234ze†
R1234yf†

Pmax(100 kPa)10.6 *1
6.8 *1
7.9 *17.1 *1
5.4 *1
7.6 †
6.8 †
6.6 †

KG
(100 kPa·m·s-1)
1415 *1
550 *1100 *1
55 *1
10 *1
11 †
9†
8†

Burning velocity(cm·s-1)
166*2
312*2
46*2
40*2
7.2*4
9†
5†
3†

Flammability limits(%)
2.5  80.0*3
4.2  75.0*3
2.1  9.5*3
15  28*5
13.3  29.3*6
7.0  9.5*6
6.2  12.3*6*1 Ref. (NFPA68, 2007[5]), Table E.1 (0.005 ft3 sphere; E = 10 J, norm. condition). *2 Ref. (NFPA68, 2007[5]), Table D.1.
*3 Ref. (Mannan, 2005[12]), Detonation limits obtained for confined tube.
*4 Ref. (ISO/DIS 817, 2010[13])*5 Ref. (NFPA325, 1994[14])*6 Ref. (JFMA, 2013[15])*7 Ref. (Mannan, 2005[12]), Table 16.4
† This work (at 35°C and wet condition)

Ef = AE/Ad × 100(2)

HAZARD ASSESSMENT• To
Flammableparameters were listed in order of KG value.
apply refrigerants safely to air-conditioning
As stated in Lunn [19], the venting efficiency Ef shallvalue,
R32,
R1234yfandR1234zeremain•JudgingfromK
equipment, the potential Grisk of combustion andbedeterminedby explosion
tests.nearly same
explosionsituations
shouldbe evaluated byrisk inasactualor lessthanAmmonia.
using the results of the laboratory-level fundamental• It should be noted that we should directly compare Ammonia with A2L
evaluation. The relationship between the deflagration
theandsame
experimental
setup conditions. => currently
indexrefrigerants
and the influenceunderon humanstructureswasconsideredwith the help of the concept of vent design
underway20

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Contents list

1. Background
2. Scale eﬀect on ﬂammability
3. Explosion severity evaluation
4. Summary21

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Explosion severity evaluation••

To apply refrigerants safely to air-conditioning equipment, the potential risk of
combustion and explosion in actual situations should be evaluated by using theresults of the laboratory-level fundamental evaluation.
•

Scale up from laboratory scale to actual scale.

•

Development of space from spherical closed vessel to rectangular unclosed
room.

•

Development of the condition from premixed concentration and verticalconcentration gradation in leakage.

The relationship between the deflagration index and the influence on human andstructures was considered with the help of the concept of vent design using KG
values.

Concentration
Distribution
Leak from door

closed vessel

Rectangular and slit

Actual room22

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Venting eﬀect on reduced pressure
According to the venting design for explosion protection, the reduced pressure effect due
to the presence of opening in the room was studied and effective area of venting was
experimentally evaluated.
Parameters for Venting effects
Pmax
Pred
Pred,maxV
L/D
KG

vent sizerectangular box
pressure release

Reduced pressure behavior for venting.

Maximum Pressure
Reduced Pressure
Max Reduced Pressure
VolumeLength/Depth ratio
Deflagration index

variable slit opening

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Explosion severity in room
Hazards due to internal explosion• There are few quantitatively-establishedinformations for internal explosion in a room.
• It is also difficult to find an internal blastresistance standard for houseroom.

Typical Values of Failure Pressures in Building Structures
Lunn, G.A., 1984. Venting Gas and Dust.
Failure Pressure (Pa)Windows(normal)

3 – 4.6

Windows(strained)

1, or even 0.2

Chipboard(19mm)

7

Brick wall (114mm)

Survived at 23, destroyed at 35

Brick wall (228mm)

Survived at 70, destroyed at 105

Resistance design for wind pressure• There are standards for wind loads on buildings (Building Standards Act, AIJ).
That is mainly concerning to external wall and roof.
• There is no standard for some kind of internal explosion load for internal wall
JIS classiﬁcation for sash and door
and ceilings.
•••

There is a classification and standard for sash
and door in JIS 4702/4706
We set reduced overpressure Pred as 1.6k.
If Pred exceeds the withstand pressure of thesash or door, the blast wind leads up to abreakup of open sash or door.

Class

Over Pressure
(Pa)

S-1

0.8k

for 1st floor window (36m/s)

S-2

1.2k

for 2nd floor window (44m/s)

S-3

1.6k

for 3rd floor window (50m/s)

S-4
S-5
S-6
S-7

2.0k
2.4k
2.8k
3.6k

indication

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Venting eﬀect on reduced pressure
A rectangular vessel 50cm on a side was prepared for the test.
A refrigerant was leaked into the vessel at the rate of 10g/min and was premixed to
stoichiometric air-fuel ratio.
The flammable behavior and reduced pressure were observed under the presence of various
vent shapes: circle, square, and rectangles with different ratio of long side and short side.
Reduced pressure effect was summarized according to vent area and aspect ratio ofrectangles.
Experimental setup• Rectangular model space• variable leaking area of slit aperture(width/height)• Electric discharge
Conditions• Mixing condition of A2L gases• 1st: premixed• 2nd: concentration gradient
Measurements• pressure measurement ：reduce eﬀect ofpressure by venting through slit
• high-speed video observation: ﬂammable behavior• temperature measurement ：achieving
temperature evaluation

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Experimental setup

a rectangular vessel

an example of opening

Schematic illustrate of experimental apparatus

risk assessment experimental facilityin Tokyo University of Science at Suwa

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dPdt (MPa/s)

ICR2015, Yokohama, Aug.16-22 2015

P_DIFmax = 1.46 [100kPa/s]
KG = 1.17 [100kPa m/s]

0.1
0.0
-0.1
-0.2

Pressure (mMPa)'150219n3'

R32 24.34vol%, 4.4ﾟC
Side Φ212mm

2
1
0
-1

Pmax = 2.89 [kPa]

-2

0

2

4

6

8

Time (s)Pressure profile
350'150219n3-Temp'

Tempeature (degC)300

R32 24.34vol%, 4.4ﾟC
Side Φ212mm
Troom = 5.60 [ºC]
Tmax = 329.90 [ºC]

250
200
150
100
50
0

0219n3

Φ212mm at side wall

0

5

10

15
Time (s)20

Temperature profile

25

30

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Contents list

1. Background
2. Scale eﬀect on ﬂammability
3. Explosion severity evaluation
4. Summary28

ICR2015, Yokohama, Aug.16-22 2015

Summary
To promote A2L refrigerants effectively and safely, the flammable behaviour of A2L
refrigerants in the presence of moisture and elevated temperatures was
experimentally investigated using a large volume combustion vessel to see the scale
and buoyancy effects.
Frame fronts of A2L refrigerants were smooth and wrinkled front was not seen in large
volume vessel even under moisture and elevated temperature conditions.
Deflagration index KG is used for estimating effect of deflagration in closed space.
There is no significant potential of increase in KG value at present.
Judging from KG value, R32, R1234yf and R1234ze remain nearly same risk as orless than Ammonia even under moisture and elevated temperature conditions.
It should be noted that we should directly compare Ammonia with A2L refrigerants
under the same experimental setup conditions.
To address the potential risk of combustion and explosion in actual situations, thereduced pressure effect by an existence of opening was examined according to the
explosion venting technology based on deflagration index KG.

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Thank you
The result of this work contributes to publish the Progress report 2014 of「the Risk Assessment of Mildly Flammable Refrigerants」
http://www.jsrae.or.jp/jsrae/committee/binensei/risk_e.html

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