Risk Assessment of Mildly Flammable Refrigerants
2013 Progress Report

April 2014

The Japan Society of Refrigerating and
Air Conditioning EngineersCopyright © 2014 by the authors and JSRAE
All rights reserved. This report or any portion thereof may not be reproduced or used in any mannerwhatsoever without the express written permission of JSRAE except for the use of brief quotations in a bookreview.
Although the authors and JSRAE have made every effort to ensure that the information in this report wascorrect at press time, the authors and JSRAE do not assume and hereby disclaim any liability to any party for
any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result fromnegligence, accident, or any other cause.
The Japan Society of Refrigerating and Air Conditioning Engineers, JSRAE
Nihonbashi-Otomi Bldg. 5F
13-7 Nihon-bashi Odenma-cho
Chuo-ku, Tokyo, 103-0011 Japan
TEL ＋81-3-5623-3223, FAX +81-3-5623-3229

Foreword
While great successes have been achieved in climate change mitigation, global emissions of greenhousegases continue to rise. Greenhouse gas emissions from fossil fuels are the main issue, but emissions offluorocarbon refrigerants from refrigeration and air conditioning appliances should not be ignored becauseof the large global warming potential (GWP) of fluorocarbons.
The progressively more severe impact of fluorocarbon refrigerants makes the need for urgent action
abundantly clear. The basic measure to reduce the impact of refrigerants is the replacement of conventionalhydrofluorocarbons (HFCs) with low-GWP refrigerants. Low-GWP refrigerants are not very stable inatmosphere and thus are sometimes flammable. According to Japan’s High Pressure Gas Safety Act, theuse of flammable refrigerants in refrigeration and air conditioning equipment is restricted in practice. For
the safe use of flammable refrigerants and relaxation of the regulation, a risk assessment needs to be
performed; only a scientific risk assessment can provide a sound basis for judgment and change inregulation.
The Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology
Development Organization (NEDO) have been subsidizing research to obtain basic information on mildly
flammable refrigerants since 2011. In addition, a research committee was set up by the Japan Society ofRefrigerating and Air Conditioning Engineers to assess the risks associated with mildly flammable
refrigerants. The Japan Refrigerating and Air Conditioning Industry Association and the Japan Automobile
Manufacturers Association are presently conducting very definitive risk assessments, and the results arebeing discussed by the research committee.
This 2013 progress report provides state-of-the-art information concerning the risk of mildly flammable
refrigerants. I am sure that its information will be of much interest for the risk assessment. I thank all themembers and observers of the committee who helped produce this progress report. I hope that you will find it
a useful and stimulating summary of the ever-sustainable story at the heart of human progress.

Chairperson of the Committee
Professor at the University of Tokyo
Eiji HIHARA
April 2014

Table of Contents
1

2Introduction
Eiji HIHARA

1~

Legal Issues with Mildly Flammable Refrigerant
2.1 Explanation of High Pressure Gas Safety Law and Legal Issues with Mildly
Flammable Refrigerant
Jun ICHIOKA and Kenji TSUJI

6

~ 11

2.2

3

4

5

6

7

8

Situation for Overseas Laws, Standards, and Regulations:
Current International Trends Regarding Refrigerant
Satoru FUJIMOTO

12 ~ 18

Eiji HIHARA, Chaobin DANG, Hiroaki OKAMOTO,
Makoto ITO, and Tomohiro HIGASHI

19 ~ 36

Shigeru KOYAMA, Yukihiro HIGASHI,
Akio MIYARA, and Ryo AKASAKA

37 ~ 47

Physical Hazard Evaluation of A2L Refrigerants Based on Several Conceivable Accident
Scenarios
Tomohiko IMAMURA and Osami SUGAWA

48 ~ 57

Progress Report of Research Institute for Innovation in Sustainable Chemistry, AIST
Kenji TAKIZAWA and Masanori TAMURA

58 ~ 71

Physical Hazard Assessment on Explosion and Combustion of A2L Class Refrigerants
Tei SABURI and Yuji WADA

72 ~ 81

Efforts of the Japan Refrigeration and Air Conditioning Industry Association (JRAIA)
8.1 Progress by Mini-Split Risk Assessment SWG
Kenji TAKAICHI, Shigeharu TAIRA, and Takeshi WATANABE

82 ~ 94

Progress at the University of Tokyo

Progress at Kyushu University

8.2

Progress of SWG for VRF System Risk Assessment
Ryuzaburo YAJIMA

8.3

9

5

95 ~ 106

Chiller SWG: Chiller Risk Assessment and Guideline Establishment
Kenji UEDA

107 ~ 119

Deregulation Activities in Japan for the Introduction of Mobile Air Conditioning Refrigerant
R1234yf
Japan Automobile Manufacturers Association, Inc.
Vehicle Maintenance Subcommittee

120 ~ 130

Member List

131 ~ 132

1. Introduction
The use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) has been widely restricted, andto protect the ozone layer, they have been replaced with hydrofluorocarbons (HFCs). However, leakage of therefrigerant into the air from active or end-of-life air conditioners is a serious environmental issue owing to its
high global warming potential (GWP). Therefore, it has been widely recognized that the replacement of HFCs
with low-GWP refrigerants is important for solving this problem. The numbers of room, package, and mobile air
conditioners shipped from Japan in 2013 were 90.1 million, 0.8 million, and 5 million, respectively. These are
the main types of air-conditioning equipment produced in Japan. With mobile air conditioners, there is highpotential for the conventional refrigerant to be replaced with R1234yf. However, studies have been conducted
over the last several years on the use of lower-GWP refrigerants for stationary air conditioners. To prevent
global warming, regulations have been imposed in Japan and overseas regarding the use of high-GWP
refrigerants such as HFCs.

1.1

Trends in Refrigerant Regulation

The EU protocol 2006/40/EC for mobile air-conditioning refrigerants, effective from January 1, 2011, prohibits
the release of new cars using refrigerants with a GWP over 150. Furthermore, starting from January 1, 2017, it
prohibits the release of any new car using such refrigerants. In 2009, the automobile industry decided to replace
the conventional refrigerant, R134a, with the low-GWP refrigerant, R1234yf. However, in April 2012, the EU
Commission temporarily permitted the continued use of R134a owing to a supply shortage of R1234yf. The
release of new model cars using refrigerants with a GWP over 150 has been prohibited since January 1, 2013.
The regulation regarding the use of stationary air conditioners is known as F-gas Regulation (EC) No. 842/2006.
The present regulation focuses on reducing refrigerant leakage from air conditioners and requires proper
management, instructional courses for operators, labeling of equipment containing F-gas, and reports byproducers, importers, and exporters of F-gas. In November 2012, the EU Commission proposed to enhance theexisting regulations. The new proposal aims to reduce the leakage of F-gas to two-thirds of the present level andprohibit the release of equipment using F-gas in fields where an environmentally friendly refrigerant has beendeveloped. To achieve this, a phase-down schedule has been proposed that assumes that the annual amount of
HFCs sold in the EU in 2015 has been reduced to one-fifth. In December 2013, the European Parliament andCouncil reached a trilogue agreement. The main points of the agreement are as follows:•

The “phase-down” schedule remains as initially proposed by the Commission;•

F-gases with GWPs above 2500 will be banned in stationary refrigeration systems from 2020, andthose with GWPs above 750 will be banned in stationary air conditioners from 2025; and•The issue of pricing or auctioning quotas is addressed through a review clause that empowers theCommission to assess a method for allocating quotas.

At the Conference of Parties, which aims to abolish practices that damage the ozone layer, three North Americancountries (US, Canada, and Mexico) submitted a proposal to revise the Montreal Protocol to restrict production
and sales of HFCs. HFCs do not damage the ozone layer. The global warming issue was caused by the
replacement of prohibited CFCs and HCFCs, which damage the ozone layer, with HFCs, which have high
GWPs. The proposal suggests restricting the distribution of HFCs in the framework of the Montreal Protocol.

1Table 1.1 and Fig. 1.1 compare the proposals and schedules of the three North American countries with those of
the EU Commission.
Table 1.1 Summary of the proposed regulation of HFCs
Proposal by three North American
EU Agreement
countries
25th meeting of the High Contracting
December 2013
Parties, October 2013
Revised edition of Regulation (EC) No.
Montreal Protocol
842/2006
19 types of HFCs
HFCs (R1234yf and R1234ze not included)(R1234yf and R1234ze not included)
Average value between 2008 and 2010
Developed countries: HFCs and 85% of
Average value between 2009 and 2012
HCFCs
Developing countries: 90% of HCFCs
Developed countries: 15% of the 2033
baseline
21% of the 2030 baseline
Developing countries: 15% of the 2043
baseline(1) Single split air-conditioning systems
containing less than 3 kg of fluorinatedgreenhouse gases with a GWP of 750 or more
shall be prohibited from 1 January 2025.
(2) The use of fluorinated greenhouse gaseswith a GWP of 2500 or more to service ormaintain refrigeration equipment with a charge
size of 40 tons of CO2 equivalent or more shallbe prohibited from 1 January 2020.
(3) From 1 January 2017 refrigeration,
air-conditioning, and heat pump equipment
charged with HFCs shall not be permitted on themarket unless the HFCs charged into thisequipment are accounted for within the quota
system.

Proposal date
Evidential law
Target refrigerants
Baselines of HFC
phase-downFinal values of
HFC phase-down

Other restrictions

Comparison with baseline (%)

120
100

EU
NA proposal (Non-A5 Parties)

100%

80

NA proposal (A5 Parties)

93%

60

90%

65%

63%

40%

45%

40

31%

20
0
2010

70%

2015

2020

30%
24%

2025

21%
2030

15%
2035

Fig. 1.1 Proposed HFC reduction stages

2

2040

2045

In Japan, the Global Environment Sub-Committee of the Central Environment Council and the Chemical andBiotechnology Sub-Committee of the Industrial Structure Council jointly created a task force and compiled an
outline for the regulation of HFCs. The document released by the task force indicated that if no additional
measures are taken, the emission of HFCs will double by 2020, and the emission from the air-conditioning
sector will account for 80% of total emissions. It highlighted the importance of integrating appropriate measuresin the air-conditioning sector. Approximately 60% of leakages in the air-conditioning sector occur during
operation; the remainder is from uncollected refrigerant from end-of-life equipment. Approximately 40% of allleakage during operation is from separate-type display cases. Conventionally, it is thought that the mostimportant alleviatory measure is the recovery of refrigerants from end-of-life refrigerators and air conditioners.
However, this is inadequate.
Based on these discussions, the "Law on regulation of management and rational use of fluorocarbons"
was established at the National Parliament on June 5, 2013. The name of the law was changed from the "Lawfor ensuring the implementation of the recovery and destruction of fluorocarbons concerning specific products."
The new law requires following the replacement of high-GWP HFCs, refrigerant management and refrigerant
recovery to reduce leakage of HFCs.
(1) Fluorocarbon manufacturers, through technology development and manufacturing of lower-GWP
refrigerants, should reduce the environmental impact.
(2) Refrigeration and air-conditioning equipment manufacturers should achieve the goal of replacing
high-GWP refrigerants with low-GWP refrigerants by the target year for each product sector.
(3) For users of commercial refrigeration and air-conditioning equipment, proper management,
installation, inspection, and repair is required.
(4) Forcollection

anddestruction

traders,aregistration

systemofcharging

fluorocarbons

for commercial refrigeration and air-conditioning equipment will be introduced, and a permit
system for recovery of fluorocarbons will also be introduced.

1.2

Research trends on the Safety of Mildly Flammable Refrigerants

The development of environmentally friendly refrigerants for room and package air conditioners is imperative tothe growth of air-conditioning technology. The low-GWP refrigerants R1234yf and R32 are promising
candidates for replacing conventional HFC refrigerants. However, these refrigerants are not very stable in air
and are flammable. Therefore, it is essential to collect basic data about the flammability of low-GWP
refrigerants and research their safety for practical use. The integration of basic information about refrigerant
physical properties, cycle performance, life cycle climate performance (LCCP), flammability, and risk
assessment will simplify their selection for practical use. These efforts are expected to contribute to theadvancement of the global air-conditioning industry.
R1234yf and R32 are less flammable than propane and R152, and are therefore classified as mildly flammable
refrigerants. In ASHRAE Standard 34, the rank 2L was set for mildly flammable refrigerants with burning heats
lower than 19 MJ/kg and burning velocities lower than 10 cm/s. Together with ammonia, R1234yf and R32 areclassified as 2L. The characteristics of flammable refrigerants are presented in Table 1.2, where LFL, UFL, BV,
and MIE denote lower flammability limit, upper flammability limit, burning velocity, and minimum ignitionenergy, respectively. Compared to propane, which is highly flammable, the other refrigerants have low BVs andhigh MIEs.

3

Table 1.2

Burning characteristics of flammable refrigerants
LFL

UFL

BV

MIE

[vol%][vol%][cm/s]

[mJ]

<3

1.8

9.5

38.7

0.246

R717 (Ammonia)

<1

15

28

7.2

21

R32

675

13.3

29.3

6.7

15

R1234yf

4

6.2

12.3

1.5

500

Refrigerant

GWP

R290 (Propane）

As illustrated in Fig. 1.2, the following conditions must be satisfied by an ignitable refrigerant that leaks from anappliance near an ignition source:(1) The refrigerant concentration must be within the required flammability range.
(2) The energy of the ignition source must be higher than the MIE.
(3) The air velocity adjacent to the ignition source must be lower than the BV.
If the air velocity adjacent to the ignition source is higher than the BV, burning will not occur because firecannot propagate against the airflow.
Rank 2L on ASHRAE Standard 34 changed the restriction on refrigerants regarding their flammability andallows for the practical use of low-flammability refrigerants. However, in Japan, only the classifications“non-flammable” and “flammable” are recognized in the High Pressure Gas Safety Act and the Ordinance on
the Security of Safety at Refrigeration. With the objective of gathering essential data for the risk assessment of
mildly flammable refrigerants, safety studies are being conducted by project teams from the Tokyo University of
Science at Suwa, Kyusyu University, University of Tokyo, and the National Institute of Advanced Industrial
Science and Technology. Since 2011, they have been sponsored by the project “Development on Highly
Efficient and Non-Freon Air Conditioning Systems” of the New Energy and Industrial Technology Development
Organization (NEDO).
Concentration
higher than LFL

Air velocity lower thanburning velocity

Existence ofan ignition source

Fig. 1.2

Ignition

Ignition mechanism

In addition, a research committee was created by the Japan Society of Refrigerating and Air Conditioning
Engineers to assess the risks associated with mildly flammable refrigerants. The Japan Refrigerating and Air
Conditioning Industry Association and the Japan Automobile Manufacturers Association are presently
undertaking risk assessments and the results are being discussed by the research committee. The 2013 activitiesof the committee to assess the risks associated with mildly flammable refrigerants are compiled in this report.
The committee members would be pleased if this report is helpful for people working in associated fields.

4

References
Directive 2006/40/EC of the European Parliament, 17 May, 2006.
Regulation (EC) No. 842/2006 of the European Parliament, 17 May, 2006.
Proposal for a Regulation of the European Parliament and the Council on Fluorinated Greenhouse Gases, 7November, 2012.
Proposal for a Regulation of the European Parliament and of the Council on fluorinated greenhouse gases, 6January 2014
Summary: North American 2013 HFC Submission to the Montreal Protocol, EPA, US, 2013.
Kenji TAKIZAWA et al., “Flammability properties of 2L refrigerants”, The International Symposium on New
Refrigerants and Environmental Technology, 2012.

5

2. Legal Issues with Mildly Flammable Refrigerant
2.1 Explanation of High Pressure Gas Safety Law and Legal Issues withMildly Flammable Refrigerant
2.1.1 Introduction
The present Refrigeration Safety Regulations recognize four classifications: inactive gases, active gases, toxic gases, and fluorocarbons otherthan inactive gases. The first three types of gases are defined by listing of those names and are demanded for an operation. An outline of theregulatory system is provided in Fig. 2.1.2.
Given the high probability that refrigerant gases with low global warming potential (GWP) will be needed in the future for a low-carbon
society, after confirming the safety of a mildly flammable gas (A2L of ISO/FDIS 817), it seems that the correspondence which cooperated
with foreign countries is also required. However, we are now having discussions with administrative authorities to clarify whether a mildly
flammable gas can be used as an inactive gas (A1) to maintain the normal state of operation.

2.1.2 Outline of High Pressure Gas Safety Law
We have some laws and regulations about a pressure to keep safety or prevent any risks, and those are operated depending on usage.
Because these laws are binding, incorrect operation is accompanied by government punishment. Although the regulatory restrictions are
based on the laws, they are basically arbitrary. We should operate without confusing the laws and regulations.
Japanese regulations on pressure (i.e. for machine safety) contain the following typical laws: 1. the High Pressure Gas Safety Law, 2.
Industrial Safety and Health Law, 3. Gas Business Law, and 4. Electricity Business Law. These laws are collectively called the four safety
laws. The High Pressure Gas Safety Law widely regulates the manufacture, operation, maintenance of package air conditioners, chilling
units, and turbo refrigerant (these are called refrigeration equipment), which are used to maintain a comfortable daily lifestyle andenvironment. An outline of the High Pressure Gas Safety Law is provided in the following.
(a) System of High Pressure Gas Safety Law
High-pressure gas safety is mainly specified by laws, government ordinancees,
ministerial ordinances, and ministerial notifications. Based on the laws, the technical standards, application procedures, inspection
procedures are minutely specified by ministerial ordinances. Government ordinances have specified exemptions to the laws, permissions for
production and storage, values that require notification reports and high pressure gases that do not require notification reports on their sales.
Ministerial ordinances are divided into several types depending on the type of business category and object of the regulation. In a ministerial
ordinance regarding refrigerant equipment, the performance was specified by Refrigeration Safety Regulations in 2001.
Law
Government ordinance
Ministerial ordinance

Ministerial notification:High Pressure Gas Safety Law.
:Order for Enforcement of High Pressure Gas Safety Law.
:1. Refrigeration Safety Regulations–regulations on production, sale, etc. of refrigerant equipment.
2. General High Pressure Gas Safety Regulations–regulations on production, sale, etc. of high-pressure
gas equipment.
3. Container Safety Regulations–regulations on cylinders containing high-pressure gases.
:1. High Pressure Gas Safety Law enforcement ordinance related notification.
2. Location of production facility notification defining the details of technical standards regarding thestructure, facility, and production method.

6

(b)Related Exemplified Standard and Operating Interpretation
Internal regulations are defined for the interpretation, operation,and individual items related to the law, government ordinances, ministerial ordinances, and ministerial notifications. The related exemplified
standard of the ministerial ordinances described above is included in this internal regulation. The standard regarding refrigerant equipment iscalled the related exemplified standard of the Refrigeration Safety Regulations. It exemplifies the technical factors of theperformance-specified ministerial ordinance in as much detail as possible and provides a specification regulation. Examples are as follows.
(Examples)
1. Safe measures against fire.
2. Structure to prevent the accumulation of refrigerant gases.
3. Pressure test, airtight test.
4. Safety apparatus that can be returned to a level below the allowable pressure.
5. Gas leak detection equipment and its installation location.
6. Materials used for refrigerant equipment.
7. Design pressure.
8. Application of standard for refrigerant equipment container.
9. Welding standard.
10. Mechanical test of weld zone.
11. Non-destructive inspection of weld zone, etc.
(c)Operation Regarding Production and Sale
In relation to the production and sale (including exports) of refrigerant equipment,
operations are regulated based on the laws (government ordinances, ministerial ordinances, ministerial notifications, etc.). These require
attention because an incorrect operation is accompanied by government punishment.

2.1.3 Daily Issue with Use of Mildly Flammable Refrigerant (example)
To use a room air conditioner, package air conditioner, or turbo refrigerating machine (hereafter called a refrigeration apparatus), thetreatment of three fundamental elements, “operation,” “charging,” and “recovery,” must be considered in daily action, and these elements
are difficult to understand. Moreover, regarding the law and its response (notification report, etc.) to each operation, all parties are involved,
especially the builders, producers, and users.
(a)Operation and Applicable Law
Although the law for a refrigeration apparatus has been adapted from the Refrigeration Safety
Regulations, it treats only “the act where a gas for refrigeration is compressed or liquefied to produce a high pressure gas.” Other acts are
regulated by other rule such as the General High Pressure Gas Safety Regulations.
(b)Charging or Recovery, and Applicable Law
When the refrigerant gas of a refrigeration apparatus has leaked, charging is an act
that produces a high pressure gas. The related law is based on the General High Pressure Gas Safety Regulations, and a notification report isrequired for every installation location. Charging with an inactive fluorocarbon or the act of recovery performed with a recovery subsystem
is excluded*1.
*1 The 2nd article 3rd clause No.6 of the High Pressure Gas Safety Law enforcement ordinance, and 2nd article of the High Pressure Gas
Safety Law enforcement ordinance-related notification.
(c)Sale and Applicable Law
The act of charging a refrigeration apparatus during an installation or repair service is not only an act of
producing, but also one of selling (whether with or without compensation) the high-pressure gas. Therefore, it is necessary to follow theGeneral High Pressure Gas Safety Regulations for commercial sales (or to include a type change notification for the high-pressure gas
regarding sales). However, because an act that uses a small container (this is called a cylinder and the internal volume is less than 1 liter)*2 is
excluded from the High Pressure Gas Safety Law, it is also exempted from the notification report on producing and selling the high-pressuregas. Moreover, when selling a class 1 refrigeration apparatus, a separate notification report on high-pressure gas dealer is also needed,7

according to the Refrigeration Safety Regulations.
*2 The 2nd article 3rd clause No. 8 of the High Pressure Gas Safety Law enforcement ordinance, and 4th article of the High Pressure Gas
Safety Law enforcement ordinance-related notification.

2.1.4 Legal Treatment of R1234yf, R1234ze(E), R32, etc.
(a)Treatment by Refrigeration Safety Regulations
Although “flammable gases,” “toxic gases,” and “inactive gases” are defined by
the second article of the Refrigeration Safety Regulations, and each refrigerant name is listed, the definition standard is not clear. Of course,
there is no definition for “mildly flammable.” At present, R1234yf, R1234ze(E), and R32 are listed neither as the inactive gases nor as
flammable gases. In this case, the easing of various regulations is not applied to R1234yf, R1234ze(E) and R32.
(b)Treatment by General High Pressure Gas Safety Regulations“Flammable gases,” “toxic gases,” and “inactive gases” aredefined by the second article of the General High Pressure Gas Safety Regulations, and the names of these gases are listed for each category.
In contrast to the Refrigeration Safety Regulations, fluorocarbons (except for flammable gases) are described under “inactive gases”, andgases (except for listed gases) with the following properties are described under “flammable gases.”
1. The lower limit for an explosion is less than 10%.
2. The difference between the higher limit and the lower limit for an explosion is more than 20%.
Figure 2.1.1 shows these types, along with where R1234yf, R1234ze(E), R32, and R717 would fall. The shaded and white parts indicate“flammable” and “non-flammable,” respectively.

Lower limit

Difference between higher limit and lower limit.
★ R1234yf

Lower limit: 6.2%
Difference: 6.1%
● R1234ze(E) Lower limit: 7%
Difference: 2.5%
◆ R32
Lower limit: 13.3%
Difference: 16%▲ R717Lower limit: 15%
Difference: 13%

Fig. 2.1.1 Measurement results based on General High Pressure Gas Safety Regulations (JFMA, 2012)(c)ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Standard
In ASHRAE, although
R1234yf, R1234ze(E), R32, and R717 were defined as “2L” by “ASHRAE standards 34” in 2010, their treatment was not clearly defined.
(d)Recovery of R1234yf, R1234ze(E), and R32
Based on a related notification from the High Pressure Gas Safety Law enforcement
ordinances, because the fluorocarbon (only an inactive gas) in the recovery equipment is being contracted out of law, R32 correspond to it.
However, R1234yf and R1234ze(E) in recovery equipment are handled based on the General High Pressure Gas Safety Regulations.

82.1.5 Issues with High Pressure Gas Safety Law regarding mildly flammable refrigerant(a)Revision of listing name principle
Although “flammable gases,” “toxic gases,” and “inactive gases” are defined by the second
article of the Refrigeration Safety Regulations and each refrigerant name is listed, the definition standard is not indicated. It is doubtful that
R413A which is classified as “A2” (mildly flammable) in “ASHRAE standard 34” (ASHRAE 34:2013) is listed as an inactive gas.
Because the treatment of a new refrigerant gas (particularly a mildly flammable gas) or a mixed gas cannot presently be determined from theviewpoint of global warming prevention, it is tackled each time while asking to Commercial Affairs Circulation Preservation Group High
Pressure Gas Preservation Section, Ministry of Economy, Trade and Industry. The “flammable” number concepts of the Refrigeration
Safety Regulations should be consistent with the General High Pressure Gas Safety Regulations.
(b)Recovery and Legislation of Refrigerant Gas That Is Not Treated As Inactive Gas
Even when classified as flammable, gases
should not be regulated uniformly. In particular, regarding a flammable gas close to an inactive gas (A2L of the mildly flammable gases),
discussions are needed to ease the regulations. Moreover, it is necessary to inquire about the establishment of technical standards for therecovery subsystem.
(Draft proposal)
1. In principle, internal fittings are restricted to welded or brazed fittings. However, if welding or brazing is not appropriate, it can be
replaced by the use of flange joints, which possess the strength required for safety (a threaded joint is inappropriate).
2. External connections are required for secure joinable coupling.
(c)Easing Requirements for Specified Equipment
Even though the refrigerant that can be used by a specified piece of equipment islimited to only an inactive fluorocarbon by a High Pressure Gas Safety Law enforcement ordinances-related notification*3, discussions arealso expected in relation to the application range of fluorocarbons that are not flammable gases.
Present state)
fluorocarbon (only an inactive gas)
Draft proposal) only a fluorocarbon that is not flammable gas*3 Ministry of International Trade and Industry notification No. 139, 6th article, 2nd clause No. 2, March 24, 1997.

2.1.6 Issues with Mildly Flammable Refrigerants from Foreign Countries
From the safety administration perspective, it is desirable to clarify several issues from a professional standpoint.
1. If R32 is listed as an inactive gas, close attention must be given to foreign countries because they might interpret the listing
differently.
2. We should clarify what is eased or changed by changing from A2 to A2L.
3. An explanation of the activities of many foreign countries is needed in the legislation.

9

Refrigerant

Outline of the regulatory system.

Classification

n/a
Other
(not applicable) producer

Normal5Class 2
producerClass 1
producer20

50 (ton)

Periodic voluntary inspection

Refrigeration Safety Manager except
R114

Fluorocarbon

Safety inspection[Inactive gas]
Listed asinactive gasses
in the second
article of afrozen security
rule

Unit
type

n/a
Other
(not applicable) producer

5

Class 2
producer

20

Class 1
producer

50 (ton)

Periodic voluntary inspection

Safety inspection (except R114)

Class 2
producerSpecifiedequipment
50 (ton)n/aNormalOther
producer

3Class 2
producer20

5Periodic voluntary inspection

Class 1
producer

50 (ton)
Periodic voluntary inspection
Refrigeration Safety Manager

Ammonia

Safety inspection (except R21)

Fluorocarbon[except
inactive gas]

Class 1 producer
n/a

Unit
type

Other
producer

3Class 2
producer

20

5Fluorocarbon (except inactive gas)

Ammonia

60 (ton)50

Periodic voluntary inspection
Safety inspection

Class 2
producern/aOther gasses[CO2, Helium,
Propane]3

Class 1
producer20

550 (ton)
Periodic voluntary inspection
Refrigeration Safety Manager (except unit type)
Safety inspection (except helium)

Fig. 2.1.2 Outline of regulation system in Refrigeration Safety Regulations (Akatsuka, 2010)10

References
Japan Fluorocarbon Manufacturers Association (JFMA), 2012, Table of environment and safety data of specific Freon (CFC/HCFC) andfluorocarbon, http://www.jfma.org/database/table.html.
Akatsuka, H., 2010, Accidents and its lessons occurred in refrigeration and air conditioning equipments, Journal of The High Pressure Gas
Safety Institute of Japan., Vol. 47, 11: p.29-45.

11

2.2 Situation for Overseas Laws, Standards, and Regulations:
Current Global Refrigerant Trends
The following describes global regulatory trends for refrigerants. Please be advised that this information may be limited in its scope and is in
no way a comprehensive account of all perspectives.

2.2.1 Trends in JapanThe Japanese government revised the current Law Concerning the Recovery and Destruction of Fluorocarbons and promulgated the new
Act on June 12, 2013. Preparations, including governmental and ministerial ordinances, are underway toward full legal enforcement
beginning on April 1, 2015. The first meeting was held on August 1, and a joint session of the Central Environment Council and theIndustrial Structure Council deliberated upon governmental and ministerial ordinances. Currently, there is a plan to promulgate, around thespring of 2014, the “guidelines for the rational use of fluorocarbons” along with a “ministerial ordinance for the decision criteria of managers
of refrigeration and air conditioning equipment” and similar ordinances. In addition, a cabinet decision concerning and subsequent
promulgation of “directives relating to designated products, etc.” are expected in 2014 in the period from the summer to autumn. Ministerial
ordnances and notifications are also scheduled for announcement during the same period. Here, the country sets GWP-based numericalvalues that take safety into account for the “designated products,” and numerical targets are imposed on product classifications for
manufacturers and importers to achieve in a specified year.
A kick-off meeting of the Industrial Structure Council, Manufacturing Industry Committee, and Chemical Policy Subcommittee was held on
November 30, 2013, and a “WG on measures to deal with Fluorocarbons” was established to deliberate on specific areas as described below.
At these meetings, the efforts made until now and the current statuses were presented. The details are as follows.
(1) Concerning the current status of efforts for independent action plans for the industry for fiscal year 2012, projections of CO2
conversion values for the amounts of HFC emissions were released, and the amount of emissions for 2012 for the field ofrefrigeration and air conditioning equipment was 2.2 million tons. Moreover, in regard to the outlook for 2020, the emissions for
HFCs used in refrigeration and air conditioning equipment are rapidly increasing and expected to reach twice the amount of current
emissions.
(2) In regard to efforts for improving refrigerant recovery, the refrigerant recovery ratio such as at the time of equipment disposal
remained stagnant at about 30%.
(3) According to a 2009 METI survey, large-scale leakage during equipment use was ascertained, and commercial-use freezing andrefrigeration equipment, in particular, had an annual leakage of 13%–17%.
(4) However, equipment developments for lower-GWP products or non-fluorocarbon products in Japan have advanced and are partiallybeing implemented.
(5) There is even a worldwide movement toward tightening the regulations for products with a high GWP, including the F-gas
Regulation in Europe and the North American proposals presented to the Montreal Protocol conferences.
Furthermore, because these affect the direction of fluorocarbon countermeasures, the following four countermeasures are being proposedto span the entire fluorocarbon lifecycle from production to destruction, adding to existing laws for fluorocarbon recovery and destruction.
(1) Promotion of a lower GWP for products using fluorocarbons or non-fluorocarbons（conversion by manufacturers of equipment andproducts）
・ Designation of special products that use fluorocarbons (air conditioners, freezers and refrigerators, blowers, etc.)
・ Decision criteria related to lower GWP concerned with designated products/promotion of non-fluorocarbons(2) Promotion of reuse of recovered refrigerant for actual phase-down of fluorocarbons (efforts by gas manufacturers)
・ Establishment of decision criteria related to the efforts (lower GWP, curbs on the manufacture and import, and recovery/reuse) ofgas manufacturers to reduce the environmental impact from fluorocarbons(3) Prevention of fluorocarbon leaks when using commercial-use refrigeration and air conditioning equipment (refrigerant management
by user)12(4)・ Establishment of decision criteria related to efforts for appropriate equipment management (periodic inspection) by user・ Refrigerant leakage amount report by user
Charge by registered contractor and reuse by licensed contractor

2.2.2 Trends in Europe
The existing F-gas Regulation in Europe was established in 2005 and came into effect in 2007. A review for a revised proposal wasscheduled in 2011. The EU Commission began an investigation for a revision in 2009, and although there was a slight delay, a revised
proposal centering on an HFC phase-down came out on November 7, 2012. For this, the European Parliament Committee submitted anamendment on June 19, 2013. The details were extremely strict and included details that prohibited the use of HFCs in stationary-type
freezers and refrigerators, along with air conditioners, in 2020. For this, the same EU Council came out with an HFC phase-down
amendment that was close to the proposal of the EU Commission. From this, a tripartite meeting was held to reconcile the views of theEuropean Commission, European Parliament Environment Committee, and EU Council, and an agreement was reached at the 4th meeting
held on December 16, 2013.
Table 1. Details of Tripartite Agreement Regarding F-Gas Regulation

Current
Regulations
HFC Prohibition

Stationary
air conditioners
Refrigerators andfreezers forcommercial use(hermeticallysealed systems )Stationary
refrigeration systems※Each member stateConsideration
for building code

Pre-charge prohibition

Cutback in amount of HFCs
placed on the market
Quota system for refrigerant
supplyResults of Tripartite Consultations

None

Single split air-conditioning systems containing less than 3 kg of F-gas with a
GWP of 750 or greater are to be prohibited from January 1, 2025.
None
Refrigerators and freezers for commercial use that contain F-gas with a GWP
of 2,500 or more are to be prohibited from January 1, 2020.
Hermetic-type refrigerators and freezers for commercial use that contain orrely upon F-gas with a GWP of 150 or more are to be prohibited fromJanuary 1, 2022.
None
Multipack centralized refrigeration systems for commercial use with acapacity of 40 kW that contain or rely upon F-gas with a GWP of 150 ormore (except in the primary refrigerant circuit of cascade systems where an
F-gas with a GWP of less than 1,500 may be used) will be prohibited fromJanuary 1, 2022.
※Exemptions for HFC prohibitions are added:
・Where technically feasible alternatives are not available or cannot be used for technical or safety
reasons, the Commission may authorize a time-limited exemption of up to 4 years following arequest of an EU Member State.
・The Commission shall collect information on the national codes, standards, or legislation ofMember States with respect to using alternative refrigerants in refrigeration and air conditioning
equipment and shall publish a synthesis report by January 1, 2017.
None
Prohibition begins from January 1, 2017. However, equipment pre-charged with
HFCs that are accounted for within the quota system may be placed on themarket. A verifiable declaration of conformity is necessary.
None
Cutback to 21% in 2030．(The Council proposal for a CO2 equivalent with theaverage total quantity for the years 2009–2012 was adopted for the baseamount.）None
Quota amount for the new market entry amount is 11%.

After approval by the Committee of the European Parliament, this revised proposal will be submitted to a vote of the plenary session of theEuropean Parliament (scheduled for March 11). Once approved by the EU Council, it will be promulgated and is expected to take effect13

from January 1, 2015.

2.2.3 Trends in United States
As for the trends in the United States, there are the North American proposals to the Montreal Protocol conferences, CACC trends,
ASHRAE standards trends, trends for revision of the UL standards, and SNAP trends. However, the AHRI refrigerant evaluation program“Low-GWP Alternative Refrigerant Evaluation Program” is primarily mentioned here. The AHRI started AREP in the spring of 2011.
Candidate alternative refrigerants are being solicited, and tests and results by standardized methods are announced. The alternativerefrigerant candidates are not prioritized, and policy is entrusted to market evaluation. In this program, a total of twenty-one companies
participated as evaluators, and five companies participated as refrigerant suppliers. Low-GWP refrigerant candidates were announced at theend of October 2012. Later, refrigerant performance was evaluated by compressor calorimeter tests, system drop-in tests, and soft-optimized
system tests, and the project’s primary period ended at the end of 2013. Because many reports have already been produced, we introduce theparticipating companies. The following URL can confirm the details.
http://www.ahrinet.org/App_Content/ahri/files/RESEARCH/AREP_Final_Reports/
Table 2.2.3.1

Companies Participating in AREP Project

US Equipment Manufacturers

Equipment Manufacturers Outside the US

Carrier Corporation

ARMINES-MINES Paris Tech (France)

Emerson Climate Technologies

Embraco Brazil（Brazil）

Goodman Manufacturing

Embraco Slovakia Sro（Slovakia）

Johnson Control Inc.

GD Midea Air-Conditioning Equip（China）

Oak Ridge National Lab.

Daikin Industries, Ltd（Japan）

Lennox Industries Inc.

Shanghai Hitachi Electrical Appliances Co., Ltd.（China）

Tecumseh Company Co.

Refrigerant manufacturers

McQuay International

Arkema Inc.

Trane/Ingersoll Rand

E.I. du Pont de Nemours and Co.

Hussmann Corp.

Honeywell International, Inc

Climate Master

Mexichem Fluor, Inc

Manitowoc Ice

Daikin Industries, Ltd

Follett Co.
Thermo King/Ingersoll Rand
University of Maryland

14

No
1

2

3
4
5

6

7

8

9

10

11

12

13

14

Table 2.2.3.2
Report Themes(Test Refrigerant)
System Drop-in Test in a
5-RT Air-Cooled Water
Chiller (R410A)

Summary of AHRI’s Low-GWP AREP Drop-in Test Reports (No. 1– No. 14)
Evaluating
Test Refrigerant
Company
Trane
Arkema ARM32a (R1234yf/R32/R125/R134a) (20:25:30:25)(US)
Arkema ARM70a (R1234yf/R32/R134a) (40:50:10)
DuPont DR5 (R1234yf/R32)(27.5:72.5)
Mexichem HPR1D (R1234ze/R32/R744)(60:6:34)
Honeywell L41a (R1234yf/R1234ze/R32) (15:12:73)
Honeywell L41b (R1234ze/R32)(27:73)
System Drop-in Test in Ice Manitowoc Honeywell L40 (R1234yf/R1234ze/R32/R152a) (20:30:40:10)
Machines (R404A)
Ice
Honeywell L41a (R1234yf/R1234ze/R32)(15:12:73)(US)
Honeywell N40b (R1234yf/R134a/R32/R125) (30:20:25:25)
System Drop-in Test in Air Oak Ridge National Refrigerant (R32/R152a)(95:5)
Source HP (R410A)Lab
System Drop-in Test in
LennoxR32
Split System HP (R410A)
Soft-optimized System
Goodman
R32
Test in 3-ton Split System
HP (R410A)
System Drop-in Test in
Trane
Arkema ARM32a (R1234yf/R32/R125/R134a) (20:25:30:25)
5-RT Air-Cooled Water(US)
DuPont DR7 (R1234yf/R32)(64:36)Chiller (Cooling Mode)
Honeywell L20 (R1234ze/R32/R152a)(35:45:20)(R22)
Mexichem LTR4X (R1234ze/R134a/R32/R125) (31:16:28:25)
Mexichem LTR6A (R1234ze/R32/R744) (63:7:30)
Daikin D52Y (R1234yf/R32/R125) (60:15:25)
System Drop-in Test in
Trane
Arkema ARM42a (R1234yf/R134a/R152a) (82:7:11)
230-RT Water-Cooled(US)
Honeywell N13a (R1234yf/R1234ze/R134a) (18:40:42)
Water Chiller (R134a)
Honeywell N13b (R1234ze/R134a)(58:42)
R1234zeE
DuPont OpteonXP10 (R1234yf/R134a) (56:44)
System Drop-in Test in
Hussmann
R1234yf
Commercial Bottle(US)
Honeywell N13a (R1234yf/R1234ze/R134a) (18:40:42)
Cooler/Freezer (R134a)
R1234zeE
DuPont OpteonXP10 (R1234yf/R134a) (56:44)
System Drop-in Test in
IngersollArkema ARM30a (R1234yf/R32)(71:29)Trailer Refrigeration Unit
Rand &
DuPont DR7 (R1234yf/R32)(64:36)
ThermoDesigned for R404A
Honeywell
L40(R1234yf/R1234ze/R32/R152a)(20:30:40:10)
King
System Soft-Optimized
LennoxHFO1234yf
Test in Split System HP(R410A)
Compressor Calorimeter
Oak Ridge R32
Test of R-410A
National
DuPont DR5 (R1234yf/R32)(27.5:72.5)
Alternatives (R410A)
Laboratory
Honeywell L41a (R1234yf/R1234ze/R32) (15:12:73)
System Drop-in Test in
Bus Air-Conditioning Unit
Designed for R134a
System Drop-in Test in
Bus Air-Conditioning Unit
Designed for R407C
System Drop-in Test in
Air-Cooled Screw Chiller(R134a)IngersollRand &ThermoKing

Mexichem AC5 (R1234ze/R32/R152a)

JohnsonControls(83:12:5)

GWP
Value
1,577
482
490
407
494
494
285
494
1,311
647
675
675

1,577
246
331
1,265
206
959
117
604
604
6
631
4
604
6
631
199
246
285
4

675
490
494
92

Honeywell N13a (R1234yf/R1234ze/R134a) (18:40:42)

604

Honeywell L20 (R1234ze/R32/R152a) (35:45:20)
Daikin D52Y (R1234yf/R32/R125) (60:15:25)

331
959

Arkema ARM42a (R1234yf/R134a/R152a) (82:7:11)

117

15

No
15

16

17
18
19
20

Table 2.2.3.3
Report Subject(Test
Refrigerant)
System Drop-in Test in
VRF Multi-Split HP(R410A)
System Drop-in Test in
Water-To-Water HP(R410A)
Compressor Calorimeter
Test (R22)
Compressor Calorimeter
Test (R134a)
Compressor Calorimeter
Test (R134a)
System Drop-in Test in
Air Source HP(R410A)

Summary of AHRI’s Low-GWP AREP Drop-in Test Reports (No. 15–No. 32)
Evaluating
Test Refrigerant
Company
Daikin
R32

GWP
Value
675

ClimateMaster(US)
EMBRACOR32
National Refrigerant (UK) (R32/R152a)(95:5)
DuPont DR5(R1234yf/R32) (27.5:72.5)
R1270

675
647
490
1.8

EMBRACOHoneywell N13a (R1234yf/R1234ze/R134a) (18:40:42)
Arkema ARM42a (R1234yf/R134a/R152a) (82:7:11)
Honeywell N13a (R1234yf/R1234ze/R134a) (18:40:42)

604
117
604

Univ.
of
Maryland:Goodmanmanufactured
Oak
Ridge
National
Laboratory

R32
Daikin D2Y-60
Honeywell L41a

675
272
494

Arkema ARM31a (R1234yf/R32/R134a) (51:28:21)
Daikin D2Y65(R1234yf/R32)(65:35)Honeywell L40 R1234yf/R1234ze/R32/R152a) (20:30:40:10)
R32/R134a(50:50)

492
239
285
1,053

Arkema ARM70a(R1234yf/R32/R134a) (40:50:10)
DuPont DR5(R1234yf/R32) (27.5:72.5)
Honeywell L41a (R1234yf/R1234ze/R32) (15:12:73)
Honeywell L41b
(R1234ze/R32)(27:73)
R32
Honeywell L41a (R1234yf/R1234ze/R32) (15:12:73)

482
491
494
494
675
494

EmersonDuPont DR5

490

DaikinMcQuay

R1234ze (E)Shanghai
Hitachi
CEP Mines
PARISTECH

R32
Arkema ARM70a
DuPont DR5(R1234yf/R32/R134a) (40:50:10)(R1234yf/R32) (27.5:72.5)

482
490

Embraco Sl

Honeywell L40

R1234yf/R1234ze/R32/R152a) (20:30:40:10)

285

Embraco Sl

DuPont DR7(R1234yf/R32) (64:36)

246

Embraco Sl

R1234yf4

Shanghai
Hitachi

R32

675

EMBRACO21

Compressor Calorimeter
Test (R404A)

22

System Drop-in Test in
Split System HP (R410A)

Carrier

23

System Soft-Optimized
Test in Air Source HP(R410A)
Compressor Calorimeter
Test in R-410A Scroll
Type
System Drop-in Test in a
200 RT Air-Cooled
Screw Chiller (R134a)
Compressor Calorimeter
Test in a R410A Rotary
System Drop-in Test in
An Air to Water HP(R410A)
Compressor Calorimeter
Test in Reciprocating
Compressors (R404A)
Compressor Calorimeter
Test in Reciprocating
Compressors (R404A)
Compressor Calorimeter
Test in Reciprocating
Compressors (R134a)
System Drop-in Test in
Split A/C System(R410A)
System Soft-Optimized
Test in Air Source

Univ.
Maryland

24

25

26
27

28

29

30

31

32

Univ.
Marylandof

Daikin D4Y

of(R1234yf/R32) (60:40)(R1234yf/R1234ze/R32) (15:12:73)(R1234yf/R32) (27.5:72.5)

6(R1234yf/R134a) (60:40)

574
675

Daikin D2Y-60

16(R1234yf/R32)(60:40)272

HP(R410A)※

Testing method reference
list

JohnsonControls･System evaluation method, reference list for evaluation results for each type ofalternative refrigerant, etc.
･Twenty-eight page report

2.2.4 International Trends
Concerning HFC regulations, there are numerous global trends, and only a few of them are presented here.

(1) The G20 Summit was held in St. Petersburg, Russia, on September 5–6, 2013. HFC countermeasures were included in an item related
to climate change in the summit statement.
〔Extract from G20 Summit Statement〕“We also support complementary initiatives, through multilateral approaches that include using the expertise and the institutionsof the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs), based on theexamination of economically viable and technically feasible alternatives. We will continue to include HFCs within the scope of
UNFCCC and its Kyoto Protocol for accounting and reporting of emissions.”(2) On June 8, 2013, the United States and China agreed at a summit meeting to cooperate toward reductions in the manufacture and useof HFCs. A global phase-down of HFCs could reduce carbon emissions by 90 Gt (CO2 conversion) by 2050, which would beequivalent to around two full years’ worth of the world's greenhouse gas emissions. The United States clearly stated HFC emission
reductions even in an action plan for countermeasures to global warming announced on June 25. President Obama emphasized in aspeech on the same day that the HFC measures by the United States and China are “a significant step in the reduction of greenhousegases.” In the past four years, the United States had, together with Canada and Mexico, jointly proposed HFC reductions under theMontreal Protocol, but countries like China had strongly opposed them. If only for this reason, it is said to be extremely significant tohave an agreement by which the two largest countries emitting greenhouse gases express the importance of HFC measures to theworld.

(3) The Twenty-Fifth Meeting of the Parties to the Montreal Protocol (MOP 25) was held in Bangkok on October 21–25, 2013.
Continuing the efforts of the previous meeting, a proposal was submitted related to regulations for HFC production and reduction. In
addition to the discussions that were held related to such issues as handling this proposal and HFC alternative refrigerant technologies,
the activities included discussions of indispensable use applications such as for methyl bromide, which is an ozone-depleting substance(ODS), and investigations such as for ODS alternatives. Amendment proposals were also submitted at this time in continuation of theprevious year’s proposals, including an amendment proposal by the three North American countries (US, Canada, and Mexico) thatseeks to amend the Montreal Protocol in order to regulate HFC production and consumption. Although there continued to be great
anxiety and resistance from some developing countries concerning this proposal, which adds to the substances subject to regulation by
the Montreal Protocol that are not ozone-depleting substances, an official discussion group was opened related to HFC control throughthe Montreal Protocol because many participating countries supported debate at the next assembly. In this discussion group, the viewsof each country were considered in relation to the Kyoto Treaty, which regulates the issues concerning the technological aspects for
HFC alternatives and funds, legal issues for cases that regulate HFCs in the Montreal Protocol, and HFC emissions. It was decided toopen a discussion group related to HFC management.

(4) In international standards, the revised proposal for ISO5149, for which debate has continued for more than 15 years, was passed after
being voted on by each country. The safety standards for equipment are structured in four parts: 1) the amount of refrigerant charge, 2)
device structure, 3) installation, and 4) certification of qualified personnel. In the 1993 edition of the current ISO5149, there are threeclassifications for refrigerants—non-flammable, flammable, and flammable and toxic—and no exceptions for the use of flammable
refrigerants are recognized. Concerning this revision, work has advanced for the introduction of new safety classifications that include
mildly flammable refrigerants. Each country voted in the middle of October 2013, and, excluding Part 4, it was rejected. However, thisrejection was mainly because of the procedure and syntax, as well as a written error in a table. There was no rejection in relation to thehandling of mildly flammable refrigerants (2L). For this reason, a revote was performed in November 2013, and it passed in January17

2014. There was a total of 27 votes for approval, with 4 votes (Part 2, 3) and 5 votes (Part 1) for disapproval. There was opposition
from the US, Australia, New Zealand, Italy, and Finland relating to Part 2 and Part 3. In ISO5149, the refrigerant charge amount isregulated corresponding to flammability. In addition, explosion proof electrical equipment is required for a flammable refrigerant whenused in such places as mechanical rooms, but mildly flammable 2L refrigerants have been excluded from this requirement.

18

3. Progress at the University of Tokyo
3.1 Introduction
According to the Kyoto Protocol, emissions of greenhouse gases, including hydrofluorocarbons (HFCs), should be
reduced. Therefore, refrigerants with low global warming potential (GWP), such as R32 and R1234yf, are expected
to be the next generation of refrigerants. However, these low-GWP refrigerants are often flammable. Table 3.1.1
lists the physical and flammability properties of the typical refrigerants (Takizawa, 2012; JFMA, 2012). Here, LFL
is the lower flammability limit, UFL is the upper flammability limit, BV is the burning velocity, and MIE is theminimum ignition energy.
To obtain information needed to assess the risks of using these refrigerants, we performed studies in the following
areas.
1. Simulation of leakage of mildly flammable refrigerants
2. Testing of thermal decomposition products of lower-GWP refrigerants
3. Risk of diesel combustion during pump-down of the heat pump
Table 3.1.1

Physical and flammability properties of low-GWP refrigerants(Takizawa, 2012; JFMA, 2012)

Refrigerant

GWP *1

LFL*2

UFL*3

BV*4

MIE*5

9.5 vol.%

38.7 cm/s 0.246 mJ

R290 (propane)<3

2.1 vol.%

R717 (ammonia)<1

15.5 vol.% 27 vol.%

R32

675

13.3 vol.% 29.3 vol.% 6.7 cm/s

15 mJ

R1234yf4

6.2 vol.%

12.3 vol.% 1.5 cm/s

200 mJ

R1234ze(E)47.0 vo.l%

9.5 vol.%

7.2 cm/s－

380–680 mJ－*1 GWP: Global warming potential*2 LFL: Lower flammable limit*3 UFL: Upper flammable limmit*4 BV: Burning velocity*5 M IE: M inimum ignition energy

3.2 Simulation of leakage of mildly flammable refrigerants
3.2.1 Introduction
When refrigerants leak into a space, they tend to accumulate at the floor of the space when they are heavier than air(Kataoka et al., 1996). As shown in Fig. 3.2.1, when the refrigerant concentration is greater than the LFL, when
there is an ignition source, and when the air velocity is lower than the burning velocity, the refrigerant may ignite.
When leakage occurs from a room air conditioner (RAC), there is always a region where the refrigerant
concentration is higher than the LFL because the refrigerant concentration is 100% near the outlet of the leakage
port. Thus, appropriate safety standards must be prepared for using air-conditioning equipment containing
flammable refrigerants, because of the risk of explosion.
It is important to understand refrigerant diffusion phenomena when preparing safety standards. It is also necessary to
clarify the effects of parameters on the diffusion phenomena of refrigerants that are heavier than air. Numericalanalysis is an effective tool for this purpose because it is very difficult to measure the diffusion of a refrigerant in alarge space. In this study, diffusion phenomena were numerically analyzed when a refrigerant leaked into a large
space from a room air conditioner (RAC), a variable refrigerant flow (VRF), and a chiller. Based on the calculation
results, the refrigerant concentration distributions, the volumes and positions of the flammable regions, and theirchanges over time were determined.

19

Concentration
higher than LFL
Ignition

Air velocity
slower thanburning velocity

Existence of
the ignition source

Fig. 3.2.1 Mechanism of ignition

3.2.2 Calculation Method
Table 3.2.1 lists the leakage scenarios considered in this study. The commercial computational fluid dynamics(CFD) program STAR-CD was used to simulate refrigerant diffusion phenomena. The problem of advection–diffusion of a mixture in a three-dimensional space is governed by the continuity, Navier–Stokes, energy
conservation, and convective diffusion equations.
Both the air and the refrigerant were assumed to be ideal gases, and the density was calculated using the equation ofstate of an ideal gas. PISO or SIMPLE was used for the pressure–velocity coupling scheme, and UD and MARS
were employed for the discretization scheme. Standard and realizable k–ε turbulence models were used in case Nos.
1–22 and Nos. 23–32, respectively. For the boundary conditions, constant flow at the inlet boundary was assumed,
and a constant pressure corresponding to the atmospheric pressure or a free outflow condition at the outlet boundary
was assumed. The law of the wall was assumed at the wall boundary.
Table 3.2.1 Leakage scenarios
case
No.
1
2

Type

Refrigerant

wall-mounted indoor unit R32
of RAC

Chargedamount
1.0 kg

3
4

R1234yf

1.4 kg5

Leakagevelocity

Ventilation air Air
flow
vent

case
No.

Type

Refrigerant

ChargedamountLeakage velocity

Ventilation air Air
flow
vent

VRF

R32

26.3 kg

10→0 kg/h

0 m3/hexist

R1234yf

29.4 kg

10 kg/h

0 m3/hnone
exist

125 g/min

0 m3/hexist

17

250 g/min

0 m3/hexist

181000 g/min

0 m3/hexist

19

0 m3/h175 g/min

0 m3/hexist

20

169 m3/hexist

350 g/min

0 m3/hexist

210→169 m3/h

exist

1400 g/min

0 m3/hexist

22

0.2 kg

50 g/min

0 m3/hexist

23

0.5 kg

125 g/min

0 m3/hexist

24

1.0 kg

250 g/min

0 m3/h

exist

25

10

floor-mounted indoor unit R32
of RACR1234yf

1.4 kg

350 g/min

0 m3/h

exist

26

11

outdoor unit of RAC

R32

1.0 kg

250 g/min

0 m3/h(outdoor)

27

R1234yf

1.4 kg

350 g/min

30 m /h(outdoor)28

R32

26.3 kg

10 kg/h

0 m3/h

none

29

14

0 m3/h

exist

30

15

169 m3/h

exist

31

16

0→169 m3/h

exist

32

6
7

R290

8
9

12
13

VRF

water-cooled chiller

R32

R1234yf

R1234ze(E)23.4 kg

23.4 kg

23.4 kg

10→0 kg/h

0 m3/hexist

75 kg/h(burst leak)

0 m3/hexist

10 kg/h(rapid leak)

0 m3/hexist

545 m3/hexist

70 kg/h(burst leak)

0 m3/hexist

9 kg/h(rapid leak)

0 m3/hexist

54 kg/h(burst leak)

7 kg/h(rapid leak)

545 m3/h

exist

0 m3/hexist

545 m3/h

exist

0 m3/hexist

545 m3/hexist

3.2.3 Analytical Model
Fig. 3.2.2 shows the geometries analyzed. The details of these geometries are described below.

(a) Leakage from a Wall-mounted Indoor RAC Unit
Refrigerant was modeled as leaking from a wall-mounted indoor unit into a space 2.8 m × 2.5 m × 2.4 m in size. The
indoor unit was located 1.8 m above the floor at the center of one of the walls. The size of the indoor unit was 0.6 m
× 0.24 m × 0.3 m, and the indoor unit had an air outlet with a size of 0.6 m × 0.06 m. The refrigerant leaked fromthis air outlet. Approximately 200,000 non-equidistant mesh points were used to discretize the governing equations.
The refrigerants considered were R32, R1234yf, and R290 (propane).

20(b) Leakage from a Floor-mounted Indoor RAC Unit
Refrigerant was modeled as leaking from a floor-mounted indoor unit into a space equal in size to that into which
refrigerant was modeled as leaking from the wall-mounted indoor unit. The indoor unit was located on the floor at
the center of one of the walls. The size of the indoor unit was 0.7 m × 0.21 m × 0.6 m, and the indoor unit had an air
outlet with a size of 0.46 m × 0.045 m. The refrigerant leaked from this air outlet. Approximately 240,000 nonequidistant mesh points were used to discretize the governing equations. The refrigerants considered were R32 andR1234yf.

(c) Leakage from an Outdoor RAC Unit
Refrigerant was modeled as leaking from an outdoor unit placed on a balcony with a size of 5.0 m × 1.2 m × 1.1 m.
The outdoor unit was located on the floor at the left side of the balcony. The size of the outdoor unit was 0.77 m ×
0.29 m × 0.68 m, and the outdoor unit had a fan that was 0.4 m in diameter. The refrigerant leaked from the fan. In
addition, wind with a velocity of 0.5 m/s was assumed to be blowing around the balcony. Approximately 350,000
non-equidistant mesh points were used to discretize the governing equations. The refrigerants considered were R32
and R1234yf.

(d) Leakage from a Variable Refrigerant Flow
Refrigerant was modeled as leaking from a VRF placed in an office with a size of 6.5 m × 6.5 m × 2.7 m. The
indoor unit of the VRF was located on the ceiling at the center of the office. This indoor unit had an air outlet thatwas 0.45 m × 0.0645 m in size and a suction that was 0.37 m in diameter. The refrigerant leaked from the air outlet
and suction. The office also had an air supply 0.2 m × 0.2 m in size and exhaust grills, and the gap under the door
was 1.5 m × 0.01 m. Approximately 200,000 non-equidistant mesh points were used to discretize the governing
equations. The refrigerants considered were R32 and R1234yf.

(e) Leakage from a Water-cooled Chiller
Refrigerant was modeled as leaking from a water-cooled chiller placed in a machine room with a size of 1.28 m ×
1.28 m × 1.28 m. The chiller, located 1.01 m from the wall, was assumed to have a nozzle-shaped leakage port 100
mm in length, located 150 mm from the floor. The inner diameter of the nozzle depended on the type of leakage: φ =4.0 mm for a rapid leakage and φ = 8.0 mm for a burst leakage.
The air inlet and exhaust duct inlet were located on the ceiling above the chiller and at the bottom of the machineroom, respectively. The areas of the air inlet and exhaust duct inlet were calculated as described below.
The velocity and openness at the air inlet and exhaust port were as follows:・・(at the air inlet)(at the air exhaust duct)

velocity: v in = 2.0 m/s, aperture ratio: α in = 0.7
velocity: v out = 4.0 m/s, aperture ratio: α out = 0.3

The air ventilation volume per hour q was calculated from the following equation.
・ Air ventilation volume: q = XV [m3/h]
where X and V are the number of air vents and the volume of the machine room (m3), respectively.
The areas of the air inlet and exhaust duct inlet, A in and A out , respectively, were obtained from the following
equation.
q = α in v in Ain = α out v out Aout
The refrigerants considered were R32, R1234yf, and R1234ze(E).
(a) wall-mounted
indoor unit of RAC(b) floor-mounted
indoor unit of RAC(c) outdoor unit of RAC(e) water-cooled chiller(d) VRF
Air supply

Opening to the air

Point 1～6

Opening to the air

RAC.

Convection

Machine room

Air supply

VRF
Exhaust port

Point 1～6

2.7 m
Under cut

21

Chiller
body
5.0 m

RAC.

2.4 m

Point 1～6

2.4 m

1.8 m

Point 1～6

2.4 m

1.1 m

Outdoor unitFig. 3.2.2 Analytical geometries

3.2.4 Results and Discussion
Table 3.2.3 presents the calculation results. The term Σ(V·t) represents the product of the flammable gas volume andthe presence time. This value is associated with the risk of combustion and is called the flammable volume time
(FVT) below. The term V FL represents the flammable gas volume, and the term V BVFL represents the flammable gas
volume with an air velocity lower than the burning velocity.

(a) Leakage from the Wall-mounted Indoor RAC Unit
The calculation results shown in Table 3.2.3 for case Nos. 1–8 represent the leakage from the wall-mounted indoor
RAC unit. As these results show, the FVT is very small, even if a mildly flammable refrigerant leaks from the wallmounted indoor unit. In addition, as the results for case Nos. 1–6 show, the FVT values determined withconsideration of the burning velocity are equal to zero. These results suggest that ignition does not occur because of
the convection caused by the refrigerant leakage, even if an ignition source exists. Therefore, no combustion occurs
if no ignition source exists inside the indoor unit. For case No. 7, although the calculated value is higher than the
maximum allowable fill ratio of propane, the refrigerant leakage represents a great hazard because the FVT value isvery high compared to those for other cases. For case No. 8, the MIE of propane is lower than R32 and R1234yf,
and the quenching distance of propane is very narrow. Therefore, leakage of propane is a hazard because a flame
transmits easily.

(b) Leakage from the Floor-mounted Indoor RAC Unit
The calculation results shown in Table 3.2.3 for case Nos. 9 and 10 represent the leakage from the floor-mounted
indoor RAC unit. According to Table 3.2.3, both the terms Σ(V FL ·t) and Σ(V BVFL ·t) are very similar. These results
suggest that the air velocity is lower than the burning velocity in the combustion region. Therefore, if an ignition
source exists in the combustion region, there is a risk of combustion throughout much of the combustion region. In
addition, because the LFL of R1234yf is lower than that of R32, the presence time of R1234yf is longer than that of
R32. Thus, the risk of combustion with R1234yf is higher than that with R32.
Therefore, safety regulations are required when flammable refrigerants are used in air conditioners because the riskof leakage from a floor-mounted indoor unit is higher than with a wall-mounted indoor unit.

(c) Leakage from the Outdoor RAC Unit
The calculation results shown in Table 3.2.3 for case Nos. 11 and 12 represent the leakage from the outdoor RAC
unit. Table 3.2.3 shows that the flammable gas volume existed for a long time, for the same reason as that explained
for the floor-mounted indoor unit. Therefore, the balcony with drains and undercuts are preferred for safety because
an outdoor unit has a fan near the floor level, which may lead to spreading of the flammable region into entire
balcony area.

(d) Leakage from the Variable Refrigerant Flow
The calculation results shown in Table 3.2.3 for case Nos. 13–22 represent the leakage from the VRF. According toTable 3.2.3, the existence of an air vent as an air supply source affects the FVT and presence time. In addition, thereleased period of the VRF is more than 150 min because of the large amount of refrigerant leaked. Therefore,
although the flammable gas volume is small, the FVT (Σ(V FL ·t)) is longer than that for leakage from a wall-mounted
RAC unit. On the other hand, the FVT decreases significantly when the air velocity is considered. For R1234yf, therisk of ignition is very low because the burning velocity is low. For R32, safety regulations pertaining to, forexample, a refrigerant leakage sensor, alarm, and ventilation are required when flammable refrigerants are used in
air conditioners.

(e) Leakage from the Water-cooled Chiller
The calculation results shown in Table 3.2.3 for case Nos. 23–32 represent the leakage from the water-cooled chiller.
Fig. 3.2.3 shows the LFL isosurface for the case in which V FL reaches its maximum value, and Fig. 3.2.4 shows how
Σ(V FL ·t) and V FL change with time. In the cases of Nos. 26, 27, and 29, calculation stopped at 100 seconds after the
refrigerant had leaked out completely, although there was a flammable region at that time. Therefore, the actual
existence time and the FVT must be larger than the values listed in Table 3.2.3. In addition, although humidity was22not considered in this study, in the case of leakage of R1234ze(E), it is important to take humidity into accountbecause this refrigerant is non-flammable when the humidity is zero.
These results indicate that the ventilation air flow has a large effect on the FVT, as do the VRF results. For example,
comparing case Nos. 24 and 25 or case Nos. 27 and 28, the effects of five numbers of ventilation times in the case of
rapid leakage of R32 and R1234yf, respectively, are evident. According to the results, in the case of rapid leakage ofboth R32 and R1234yf, Σ(V FL ·t) is very small and Σ(V BVFL ·t) equals zero, because the ventilation air makes therefrigerant flow through the exhaust duct to the outlet. This result might be attributed to the large number ofventilation times. On the other hand, for the non-ventilation case, the FVT of R1234yf is larger than that of R32,
because the LFL of R1234yf is lower than that of R32 and the presence time of R1234yf is longer than that of R32,
as described before.
Furthermore, the leakage velocity was assumed to be much higher than that in case of leakage from an RAC or VRF,
which leads to a zero or very small Σ(V BVFL ·t), even if Σ(V FL ·t) increases. However, if there is no ventilation air flow
and there is a high-concentration region after the refrigerant leaks out completely, as in case Nos. 26, 27, and 29,
Σ(V BVFL ·t) might increase.
The results for the leakage from the water-cooled chiller indicate that sufficient ventilation air flow is needed tokeep the room safe when flammable refrigerants are used in chillers. A leakage sensor is also required.

3.2.5 Results of the Simulation of Leakage of Mildly Flammable Refrigerants
The simulation and experiments conducted in this study to examine leakage of refrigerants into a space yielded thefollowing findings.
1. In the case of leakage from a wall-mounted indoor unit, combustion does not occur if an ignition source does
not exist inside the indoor unit.
2. In the case of leakage from a floor-mounted indoor unit, safety regulations are required when flammable
refrigerants are used in air conditioners.
3. In the case of leakage from a floor-mounted indoor unit or outdoor unit, the risk of combustion is higher with
R1234yf than with R32.
4. In the case of leakage from an outdoor unit, the balcony with drains and undercuts are preferred for safety
because an outdoor unit has a fan near the floor level, which may lead to spreading of the flammable region
into entire balcony area.
5. In the case of leakage from a VRF, when the burning velocity is considered, the FVT is much smaller.
6. In the case of leakage from a water-cooled chiller, the ventilation air flow has a large effect on the FVT. When
there is no ventilation air flow and the velocity of the refrigerant leakage is high, the FVT might increase after
the refrigerant leaks out completely.

23

Table 3.2.3 Predicted Σ(V FL ·t) and Σ(V BVFL ·t)Σ(V FL ·t ),Σ(V BVFL ·t ),

3

m min

3

m min

case
No.

Presence time,minΣ(V FL ·t ),Σ(V BVFL ·t ),

3

m min

m3 min8.36

3.14×10-2

018176.47

2.152

0

0

19

176.42

0.661

0

0

20

176.41

0.583

0

0

21

176.41

0.592

22

10.25

case
No.

Presence time,
min

1

4.01

1.18×10-2

0

17

2

4.01

-2

0

-3
-2
-2
-2

3

1.23×108.01

49.79×108.01

1.07×10

0

5

1.03

6

1.05

4.34×100

2.14×100

71473.00

7689

7688

23

18.72

0.013

0

3.73×10

-2

8

4.73

0.258

0.161

24

140.400.599

0.0000229111.00136.83136.8125

140.400.002

0507.50*1

up to22.62

up to 127.84

up to 3.449*1

up to 157.67

up to 1108.44

up to 44.15

1011

309.00507.82

26

45.00

43.01

42.50

27

12

93.00

62.54

61.53

28

156.00

0.008

0

13

157.85

1.622

0.021

*1

29

up to 27.67

up to 361.62

0 *2

14

157.82

0.831

0.011

30

26.00

0.014

0 *2

15

157.82

0.702

0.014

31

200.5816.3520 *2

16157.82

0.725

0.011

32

200.58

0.009

0 *2

*1 the condition that calculation stopped at 100 second after refrigerant completely leaked out*2 R1234ze(E) is non-flammable on the condition whose relative humidity equals zerocase No.23

case No.24

case No.25

case No.26

case No.27

R32, burst leakage
ventilation: 0 m3/h

R32, rapid leakage
ventilation: 0 m3/h

R32, rapid leakage
ventilation: 545 m3/h

R1234yf, burst leakage
ventilation: 0 m3/h

R1234yf, rapid leakage
ventilation: 0 m3/h

t = 1120 sec

t = 8400 sec

t = 8400 sec

t = 1287 sec

t = 9360 sec

case No.28

case No.29

case No.30

case No.31

case No.32

R1234yfburst leakage
ventilation: 545 m3/h

R1234ze(E)burst leakage
ventilation: 0 m3/h

R1234ze(E)burst leakage
ventilation: 545 m3/h

R1234ze(E)rapid leakage
ventilation: 0 m3/h

R1234ze(E)rapid leakage
ventilation: 545 m3/h

t = 9360 sec

t = 1560 sec

t = 1560 sec

t = 10200 sec

t = 10200 sec

Fig. 3.2.3 LFL isosurface when V FL reaches its maximum value

24

case No.23

case No.24

case No.25

R32, burst leakage
ventilation: 0 m3/h

R32, rapid leakage
ventilation: 0 m3/h

R32, rapid leakage
ventilation: 545 m3/h

0.002

0.004

0.001

0

0
4

8
12 16
time [min]

0.15

0.4

0.1

0.2

0.05

0

20

0

0
20 40 60 80 100 120 140
time [min]0case No.28
R1234yf, burst leakage
ventilation: 545 m3/h

1500

30

8
12 16
time [min]

6

10

300

3

0

0

VFL [m3]

9

600

20

0
0

25

case No.30

case No.31

R1234ze(E), burst leakage
ventilation: 545 m3/h

R1234ze(E), rapid leakage
ventilation: 0 m3/h

50

500

8
6

400

4

200

2

0

0
0

R1234ze(E), burst leakage
ventilation: 0 m3/h

25

50 75 100 125 150
time [min]case No.32

20

100

Flammable volume

600

50 75 100 125 150
time [min]case No.29
1500

10
Cumulative flammable volume time

900

20

4

800

VFL [m3]

90

0

1000

12

Σ(VFL t) [×10-5 m3min]

40

Flammable volume

1200
Σ(VFL t) [m3min]

120

60

15
Cumulative flammable volume time

50

R1234ze(E), rapid leakage
ventilation: 545 m3/h
1000

0.3

10

Cumulative flammable volume time

Cumulative flammable volume time

Cumulative flammable volume time

Flammable volume

Flammable volume

Flammable volume

Flammable volume

100

10

0

0
5

10 15 20time [min]

25

0.18

8

0.12

20

4

0.06

0

0

60

600

40

300
0
0

4

8

0.24

12

900

0
0

12 16 20 24 28
time [min]VFL [m3]

20

16

80
VFL [×10-5 m3]

200

1200

Σ(VFL t) [m3min]30

VFL [m3]

40

300

50

100
150
time [min]200Σ(VFL t) [×10-5 m3min]

Cumulative flammable volume timeΣ(VFL t) [×10-5 m3min]

Σ(VFL t) [m3min]

2

R1234yf, rapid leakage
ventilation: 0 m3/h

30Σ(VFL t) [m3min]

4200case No.27
60

0

400

R1234yf, burst leakage
ventilation: 0 m3/h
Flammable volume400

620 40 60 80 100 120 140
time [min]Cumulative flammable volume time

0

8

600

0
0

Flammable volume

800

case No.26
180
150

10
Cumulative flammable volume time

VFL [m3]
Σ(VFL t) [×10-5 m3min]

0.008

Σ(VF t) [m3min]

0.003

0.6
VFL [m3]

Σ(VFL t) [m3min]

0.012

0

1000

0.2
Flammable volume

0.004

VFL [×10-5 m3]

0.8
Cumulative flammable volume time

Flammable volume

VFL [×10-5 m3]

0.005
Cumulative flammable volume time

800

8

600

6

400

4

200

2

0

VFL [×10-5 m3]

0.02
0.016

0
0

40

80 120 160
time [min]200

Fig. 3.2.4 Σ(V FL ·t) and V FL changes with time

3.3 Thermal decomposition products of lower-GWP refrigerants
3.3.1

Introduction

To analyze the risks of using lower-GWP refrigerants, it is necessary to clarify their decomposability and products.
However, the high reactivities of products such as hydrogen fluoride (HF) make this quantification difficult.
Moreover, Takizawa et al. (2011) has suggested that the reactivity of a molecule with more fluorine atoms thanhydrogen atoms, such as R1234yf, is affected by humidity. Thus, its flammability limits and product composition
depend on the relative humidity of the surrounding air.
The experiment described in this section was carried out to quantify HF, the main toxic product, and to analyze otherproducts in the thermal decomposition of refrigerants.

3.3.2

Experimental Apparatus and Methods(a) Experimental Apparatus
There are two causes of HF generation from refrigerants: thermal decomposition by heating and combustion. In thisresearch, only thermal decomposition was studied. A schematic diagram of the experimental apparatus fabricated to
study thermal decomposition by heating is shown in Fig. 3.1.1. This experimental apparatus consisted of four parts:
gas mixing, heating, measuring, and detoxification parts.
The gas mixing part was used to mix refrigerant and air at a specified concentration and humidity. The concentration
was controlled by mass flow controllers, and the humidity was controlled by a dehumidifier and humidifier. The
heating part was used to heat a gas sample and make it react in a straight Inconel 600 pipe (inner diameter 10.7 mm)

25

or mullite (3AlO 3 ·2SiO 2 ) pipe (inner diameter 11 mm), and included a 550-mm-long electric furnace around thepipe. Three thermocouples were set on the outside wall, and for the mullite tube, three additional thermocouples
were set on the inside wall of the pipe. To prevent these thermocouples from corroding, the inside ones were
mounted in a mullite protection tube with an outer diameter of 6 mm. The gas sample flowed in the gap, 2.5 mm
wide, with a cross-sectional area of 0.67 cm2, between the two tubes. The measuring part consisted of gas cells for
Fourier transform infrared spectroscopy (FT-IR). To broaden the concentration measurement range, two cells withdifferent path lengths were used. The detoxification part consisted of an absorbance tube that exhausted into a fumehood
refrigerantsgascylinderaircompressor

MFC
humidifier

heating tube

MFC

FT-IR
gas cell(10cm)

dehumidifier
exhaustFT-IR: Fourier transform infrared spectroscopy
MFC: mass flow controller

FT-IR
gas cell(12m)

Fig. 3.3.1 Schematic diagram of the experimental apparatus(b) Materials Tested
The materials tested were mixtures of refrigerants (R32, R1234yf, and R134a) and air.

(c) Measuring Instruments
An FT/IR-4200 (by JASCO), gas cell (temperature-controlled, 10-cm path length, by Harrick), and CaF 2 windows
were used to measure the concentrations of the refrigerants and products.
To avoid instrument corrosion caused by the HF, FT-IR was conducted using a detector that was not exposed to thesample gas.

(d) Quantifying Method
Each molecule was quantified by absorption in particular wavenumbers. For refrigerants, criteria were establishedfrom measurements taken while the electric furnace was off and was at room temperature. For HF and COF 2 , datafrom Northwest-Infrared (PNNL, 2012) were used as criteria.

(e) Experimental Conditions
The following parameters were used as the experimental conditions.
1) Temperature of the heater: up to 700°C
2) Concentration of the refrigerant: four points under its LFL
3) Total flow rate: 100–200 ml/min4) Humidity: up to 60% RH

3.3.3 Results and Discussion(a) Results for the Inconel Tube
The concentrations of refrigerant, HF, and COF 2 after heating versus the heater temperature are shown below foreach refrigerant. The variable parameter is absolute humidity [g/m3], and the fixed parameters are the refrigerant
concentration (2.5 vol. %) and the total flow rate (200 ml/min.).

26

3
2.5
2
1.5
1
0.5
0
-0.5
450

550

650

concentration of HF [vol.%]concentration of R32 [vol.%]

・R32
The concentrations of R32 and HF in the case of R32 testing are shown in Figs. 3.3.2 and 3.3.3. A decrease in theR32 concentration and an increase in the HF concentration began when the heater temperature was in the range of570–590°C. The amount of COF 2 generated was less than 0.01 vol. %. In addition, the decrease in the R32
concentration was not affected by the humidity.

750

2.5

< 3[g/m3]

2< 5[g/m3]

1.5< 7[g/m3]

1< 9[g/m3]

0.5< 12[g/m3]0450Temperature of heater [°C]

550

650

750

Temperature of heater [°C]Fig. 3.3.2 Concentration of R32 versus heater temperaturetemperature (total 200 ml/min, 2.5 vol.% with air)Fig. 3.3.3 Concentration of HF versus heater(total 200 ml/min, 2.5 vol.% with air)・R1234yf
The concentrations of R1234yf, HF, and COF 2 in the case of R1234yf testing are shown in Figs. 3.3.4, 3.3.5, and3.3.6. In this experiment, the results gradually changed when the experiment was repeated using the same tube.
Before the change, the decrease in the R1234yf concentration and the increase in the HF concentration began when
the heater temperature was in the range of 500–550°C, and generation of COF 2 began at 600°C. In addition, thedecrease in the R1234yf concentration was not affected by the humidity. After the change, the decrease in theR1234yf concentration started at a lower temperature, and at a given temperature, the concentration of R1234yf was
lower and the concentration of one of the products was higher than before the change. Moreover, the decrease in theR1234yf concentration was affected by the humidity.
concentration of HF [vol.%]concentration of
R1234yf [vol.%]

3
2.5
2
1.5
1
0.5
0
350

450

550

650

750

Temperature of heater [°C]

2.5
2
1.5
1
0.5
0
350

450

550

650

Temperature of heater [°C]Fig. 3.3.4 Concentration of R1234yf versus heater temperature Fig. 3.3.5 Concentration of HF versus heatertemperature(total 200 ml/min, 2.5 vol.% with air)
(total 200 ml/min, 2.5 vol.% with air)

27

750

Concentration of
COF2 [vol.%]

1.4
1.2
1
0.8
0.6
0.4
0.2
0

< 3[g/m3]< 5[g/m3]< 7[g/m3]< 9[g/m3]< 11[g/m3]< 13[g/m3]

350

450

550

650

750

Temperature of heater [°C]Fig. 3.3.6 Concentration of COF 2 versus heater temperature(total 200 ml/min, 2.5 vol.% with air)・R134aThe concentrations of R134a, HF, and COF 2 in the case of R134a testing are shown in Figs. 3.3.7, 3.3.8, and 3.3.9.
The decrease in the R134a concentration and the increase in the HF concentration began when the heatertemperature was in the range of 500–550°C, and generation of COF 2 began when the temperature exceeded 650°C.
The decrease in the R134a concentration was not affected by the humidity.
2.5

Concentration of
HF [vol.%]

Concentration of
R134a [vol.%]

3
2
1.5
1
0.5
0
450

550

650

750

450

Temperature of heater [°C]

Concentration of
COF2 [vol.%]

0.4< 3[g/m3]

0.3< 5[g/m3]

0.2< 7[g/m3]< 9[g/m3]

0.1
0
650

650

750

Fig. 3.3.8 Concentration of HF versus heater

0.5

550

550

Temperature of heater [°C]Fig. 3.3.7 Concentration of R134a versus heater temperaturetemperature(total 200 ml/min, 2.5 vol.% with air)

450

0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

750

Temperature of heater [°C]Fig. 3.3.9 Concentration of COF 2 versus heater temperature(total 200 ml/min, 2.5 vol.% with air)

28

(total 200 ml/min, 2.5 vol.% with air)(b) Discussion for the Inconel Tube
Even though an Inconel tube was used to avoid reducing the repeatability of the tests, changes occurred during theR1234yf testing. In addition, soot dust was found in the tube. Removal of such soot dust is expected to improve therepeatability of the tests.

(c) Results for the Mullite Tube
The remain rates of the refrigerants are plotted against the heater temperature without humidification in Figs. 3.3.10
and 3.3.11. The variable parameter is the refrigerant concentration (vol. %), and the flow rate shown is the total forthe refrigerant and air. For both refrigerants, there was little decomposition when the heater temperature was 500°C
or lower, but when the heater temperature was 550°C or higher, the remain rate decreased. The remain rates ofR1234yf are plotted against the humidity before heating in Figs. 3.3.12 and 3.3.13. Takizawa et al. has suggested
that the reactivity of R1234yf is affected by humidity, but these results do not show the reactivity of the refrigerant
being affected by the humidity during testing. The amount of HF generated in the experiment illustrated in Fig.
3.3.10 is shown in Fig. 3.3.14. As the temperature and/or concentration increased, the generation of HF also
increased. However, although it was expected that the HF concentration would be proportional to the R32
concentration, the effect of the concentration was much smaller, and the amount of HF generated was 1/ 10 –1/ 30 of the1
0.8

Remain rate of R1234yf [-]Remain rate of R32 [-]value estimated from the decomposition of R32.

3.3%

0.6

6.6%

0.4

9.7%

0.2

12.8%

0
450

550

650

750

Temperature of heater [°C]

1

400℃

0.8

500℃

0.6

550℃

0.4

600℃

0.2

650℃

0
0

20

40

60

Humidity before heating [%RH]

0.8

1.4%

0.6

2.8%

0.4

4.3%

0.2

5.8%

0
450

550

650

750

Temperature of heater [°C]Fig. 3.3.11 Remain rate of R1234yf versus heater(dry, total 100 ml/min with air)Remain rate of R1234yf [-]Remain rate of R1234yf [-]Fig. 3.3.10 Remain rate of R32 versus heater temperaturetemperature(dry, total 100 ml/min with air)

1

1
400℃

0.8

500℃

0.6

550℃

0.4

600℃

0.2
0

650℃
0

20

40

Humidity before heating [%RH]

Fig. 3.3.12 Remain rate of R1234yf versus humidity
humidity(total 100 ml/min, 2.8 vol. % in air)Fig. 3.3.13 Remain rate of R1234yf versus(total 200 ml/min, 2.8 vol. % in air)29

60

concentration of HF [ppm]

10000
8000

3.3%

6000

6.6%

4000

9.7%

2000

12.8%

0
450

550

650

750

Temperature of heater [°C]Fig. 3.3.14 Hydrogen fluoride versus heater temperature(R32, dry, total 100 ml/min with air)(d) Discussion for the Mullite Tube
In the experiment conducted with R1234yf, the amount of HF generated was too small to detect. It is believed that
this does not mean that no HF was generated but rather that the R1234yf or its decomposition products trapped the
HF on the wall of the heating pipe. However, the mechanism for this trapping is not clear. The chemical reactions
that occur in the thermal decomposition of the refrigerants considered are shown.
For R32:
CH 2 F 2 + O 2 → 2HF + CO 2,
For R1234yf:
In the absence of H 2 O,
CF CF=CH + 5/2O → 2CO + COF + 2HF
3

2

2

2

2

In the presence of H 2 O,
CF CF=CH + 5/2O + x(H O)
3222→ (2+x)CO + (1-x)COF + 2(1+x)HF
2

2

However, in the experiments conducted in this research, not only was the amount of HF generated lower than theestimated value, but the COF 2 peak at approximately 1,930 cm-1 was also not detected when the R1234yf
concentration was sufficiently high to consume the humidity (H 2 O) in the air. The reason for the absence ofR1234yf was assumed to be a reaction between the wall and HF that can be expressed as AlO 3 + 3HF → AlF 3 +3/2H 2 O + 3/4O 2 . This reaction produced H 2 O, which reacted with the COF 2 . It is not clear why no HF was
detected in the experiment conducted with R1234yf. However, after this experiment, when only air flowed and theheater were set at 600°C, HF was detected after one or two hours. This suggests that the trapping of HF on the wall
was facilitated more by R1234yf than by R32.

3.3.4 Conclusions Concerning Thermal Decomposition Products of Lower-GWP
Refrigerants
For two lower-GWP refrigerants and a conventional refrigerant, the lower-limit temperatures of thermal
decomposition and the amounts of decomposition products were measured in a way that was relatively unaffectedby the wall material. In future experiments, we plan to reduce the effect of soot in the pipe used, employ common
wall materials such as stainless steel, and examine reaction rates and mechanisms.

30

3.4. Risk of Diesel combustion during pump-down of the heat pump
3.4.1 Introduction
During the pumping down of refrigerants (refrigerant collection) in heat pump equipment, the lubricant oil and therefrigerant may reach the self-ignition combustion point as the temperature rises due to adiabatic compression of thegaseous mixture of a flammable refrigerant, lubricant oil, and air. This phenomenon has caused incidents ofaccidental destruction of outdoor air conditioning units (TRK, Tokyo Metropolitan Government, 2012). Because of
the mild flammability of R1234yf and R32, which are considered low-GWP refrigerants, it is necessary to estimate
their safety in comparison to R410A, which is a nonflammable refrigerant (JFMA, 2012). This section describes an
examination of the differences in the combustion conditions for each refrigerant conducted using an experimental
apparatus to reproduce diesel explosions. It must be kept in mind that the results shown here do not indicated thatthe refrigerants tested pose high combustion risks. It is the nature of the apparatus used and the conditions of theexperiments that made it easy to induce diesel explosions.

3.4.2 Experimental Device and Method
Fig. 3.4.1 below shows a schematic diagram of the equipment used in the experiment. The equipment’s main
components are an air supply system, a refrigerant supply system, a temperature control system, a lubricant oil
supply system, and a compressor (model engine) driven by a motor.

Fig. 3.4.1 Experimental apparatus(a) Air Supply System
The air is compressed to 0.7 MPa by a compressor (oil-free air compressor 39L/ACP-160SL, made by EARTHMAN), passes through a dehumidifier (air dryer GK3103D-AC100V, made by CKD), and is reduced to a pressureof 0.3 MPa by a pressure regulator (AR20-02BE, made by SMC). The flow rate is controlled by the mass flow
controller (MODEL8550MC-0-1-1, made by Kofloc).

(b) Refrigerant Supply System
The vapor refrigerant from the refrigerant bomb is reduced to a pressure of 0.3 MPa by a pressure regulator(SRSERIES, made by Yamato Sangyo). The flow rate is controlled by the mass flow controller (FCST1500FC-8J3F400L-N2, made by Fujikin). The refrigerant mixes with the air.

(c) Temperature Control System

31

The temperature of the gaseous mixture of the air and the refrigerant is measured by a sheathed thermocouple and iscontrolled by heater 1 and the temperature controller (FHP-201, made by Tokyo Garasu Kiki, TC-1000, made by As
one). Heater 2 controls the temperature of the model engine to equalize the temperature of the engine intake gas andthat of the engine surface. These heaters are used to establish experimental conditions that make it easy to induce an
explosion.

(d) Lubricant Oil Supply System
The lubricant oil exits the oil tank and passes through the flow meter (micro-flow meter MODEL213-311/295, madeby TOYO CONTROL). The oil is then raised to a pressure of 150–180 MPa by the oil injection system (a common
rail electric control fuel injection system, made by FC DESIGN) and is injected in the form of a spray. The timing of
the injection is determined using an encoder and a stroke sensor fitted to the engine.

(e) Compressor
The model engine (R155-4C, made by ENYA, 4 cycle, 25.42-cc stroke volume, 16.0 compression ratio) is used as acompressor and is driven by a motor (MELSERVO-J3, made by Mitsubishi Electric) that is directly connected to its
stroke shaft. A computer controls the number of revolutions per minute.

(f) Measuring System
The temperatures of the intake and exhaust gas of the engine are measured using sheathed thermocouples. The
pressure in the engine is measured using a pressure gauge (6045A, made by KISTLER). The engine crank angle ismeasured using an encoder. These measurements, along with the flow rate of the oil and an injecting signal, arerecorded by a computer using a data logger (data logger system NR-2000, made by KEYENCE). The exhaust gas isanalyzed using an FT/IR (Fourier transform infrared spectrometer FT/IR-4700, made by Jasco).

(g) Experimental Method
Table 3.4.1 lists the refrigerants and the lubricant oil used in the experiment. In addition to R410A (the main
existing refrigerant), R1234yf and R32 (new refrigerants), as well as R134a (a pure nonflammable refrigerant) andnitrogen gas (inert gas), were used for comparison. The flow rate of the oil was determined from the theoretical
air/fuel ratio, which is calculated from the air flow ratio determined by the number of revolutions per minute and thestroke volume of the engine. The calculated theoretical air/fuel ratio was 9.5, according to the results of a CHO
analysis of the oil conducted by SVC Tokyo. The experimental parameters were the number of revolutions per
minute, the refrigerant, and the concentration of the refrigerant.

Item

Table 3.4.1 Refrigerant and lubricant oil
Test substance

Refrigerant

R1234fy, R32, R410A, R134a, N2

Lubricant oil

PAG (VG46)

We investigated the self-ignition combustion of a gaseous mixture of air and lubricant oil in experiment 1. Table
3.4.2 lists the conditions of the experiment. The flow rate of the oil was set to the theoretical air/fuel ratio. We
measured the differences in the pressure in the engine caused by the injection of the air–oil mixture.
Table 3.4.2 Conditions of experiment 1

Air-oil mixing gas
500-1500
Number of revolutions, rpm
6.3-18.8
Air flow rate, l/min
Inlet gas temperature, °C
250(0.765-2.295)×10-4
Oil flow rate, l/min
In experiment 2, we measured the self-ignition combustion of gaseous mixtures of air, refrigerant, and lubricant oil,for a range of refrigerant concentrations. Table 3.4.3 lists the conditions of the experiment. The flow rate of the oil
was fixed for any given concentration of the refrigerant.

32

Table 3.4.3 Conditions of experiment 2

Air-refrigerant-oil mixing gas
500-1500
Number of revolutions, rpm
0-100
Refrigerant concentration, vol%6.3-18.8
Mixture flow rate, l/min
Inlet gas temperature, °C
260(0.765-2.295)×10-4
Oil flow rate, l/min
We measured the exhaust gas of the gaseous mixture of the air, refrigerant, and lubricant oil at self-ignition
combustion by FT/IR. Table 3.4.4 lists the conditions of the experiment. Northwest-Infrared data were used for
identification of the products (PNNL, 2012). We used a spectrum of 4,039 cm-1 for quantitative analysis of the HF toavoid noise caused by H 2 O and CO 2 .
Table 3.4.4 Conditions of experiment 3

Air-refrigerant-oil mixing gas
1500
Number of revolutions, rpm
20, 30(R32)
Refrigerant concentration, vol%18.8
Mixture flow rate, l/min
Inlet gas temperature, °C
260
2.295×10-4
Oil flow rate, l/min

3.4.3 Results
In experiment 1, we examined the change in the pressure in the engine due to the presence of the lubricant oil. In
experiment 2, we reproduced the state of air mixing at pump-down by changing the concentration of the refrigerant
and measured the pressure in the engine. We examined the effect of the refrigerant on the pressure rise in the engine
by analyzing the exhaust gas.

(a) Results of Experiment 1
Fig. 3.4.2 shows the representative pressure changes in the engine when the gaseous mixture of air and lubricant oil
was compressed. The number of revolutions per minute was 1,500 rpm, and the temperature of the intake gas was
25°C. The horizontal axis shows the crank angle, which reached the top dead center at 360°. The engine moved
smoothly without the injection of the oil, which indicates that combustion did not occur. The pressure rose
drastically with the injection of the oil. The exhaust gas changed to white and a loud noise and strong vibration wereobserved. It is possible that the lubricant oil self-ignited because of the temperature increased induced by adiabatic
compression.

Pressure[MPa]5
without_oil

4

with_oil
3
2
1
0
180

240

300
360
420
Angle[degree]

480

540

Fig. 3.4.2 Pressure in the engine(b) Result of Experiment 2
Figs. 3.4.3 and Fig. 3.4.4 show the representative pressure change in the engine when the gaseous mixture of air,refrigerant, and lubricant oil was compressed, for refrigerants R1234yf and R134a, respectively. The number of
revolutions was 1,500 rpm.

33

In the case of R1234yf, self-ignition combustion occurred and the pressure rose when the refrigerant concentration
was 0%, which is similar to the results of experiment 1. The exhaust gas was white at this point. When the
refrigerant concentration was more than 30–40%, no drastic rise in the pressure was observed and little white gas
was observed. The maximum pressure decreased as the concentration of the refrigerant increased. At low refrigerant
concentrations, the pressure increased more than the pressure at 0% concentration. The maximum pressure then rose
to approximately 5 MPa. At this point, the color of the exhaust gas changed to black, and intense noise and vibration
occurred. As the concentration of the refrigerant decreased, the maximum pressure decreased.
Combustion did not occur at any concentration of the refrigerant without the injection of oil. The exhaust gas wasneither white nor black, and the engine moved smoothly. These results were similar to those for R1234yf, R32, andR410A.
5

5

4

Pressure[MPa]Pressure[MPa]0%ref20%ref3

89.3%ref

2
1

0%ref
30%ref
100%ref

4
3
2
1
0

0
180

240

300
360
420
480
540
Angle[degree]
Fig. 3.4.3 Pressure in the engine with an R1234yf
gas mixture

180

240

300

360

420

480

540

Angle[degree]
Fig. 3.4.4 Pressure in the engine with an R134a
gas mixtureWith R134a and N 2 , on the other hand, combustion did not occur at refrigerant concentrations of more than 70%,
and the engine moved smoothly. Combustion occurred at refrigerant concentrations of less than 50%. The exhaustgas was white and there was a slight vibration. The emission of black exhaust gas and the intense vibration that
occurred with the previous refrigerant did not occur in this case. The maximum pressure increased as theconcentration of the refrigerant decreased and reached a maximum when the concentration of the refrigerant reached
0%.
Fig. 3.4.5 and Fig. 3.4.6 show the results of experiment 2. The horizontal axis shows the volume concentration of
the refrigerant, and the vertical axis shows the maximum pressure normalized with respect to the pressure at a
refrigerant concentration of 0%. The theoretical value was calculated by assuming adiabatic compression, based on
the ratio of the specific heat of the air to that of the refrigerant.
In the case of R1234yf, when the refrigerant concentration was greater than 50%, self-ignition did not occur, and the
maximum pressure was almost equal to the pressure without the oil. The maximum pressure increased as theconcentration of the refrigerant decreased, presumably because of the change in the ratio of the specific heat of the
air to that of the refrigerant. Self-ignition occurred when the concentration of the refrigerant decreased further. At
that point, the maximum pressure was higher than that of the air only, which implies that the refrigerant itself caused
the combustion reaction. These results were similar to those for R32 and R410A.
In the case of R134a, as in the case of R1234yf, self-ignition did not occur at the high end of the range of refrigerant
concentrations. Self-ignition occurred when the concentration of the refrigerant decreased; however, the maximum
pressure was lower than that of R1234yf and reached a maximum at a refrigerant concentration of 0%, whichsuggests that combustion of the refrigerant itself did not occur. These results were similar to those for N 2 .

34

3

3
theoretical value
with_oilwithout_oil

2

theoretical value
with_oilwithout_oil

2.5
Pressure[-]Pressure[-]

2.5
1.5
1
0.5

2
1.5
1
0.5

0

0
0

25
50
75
100
Concentration[vol%]Fig. 3.4.5 Maximum pressure in the engine
versus the concentration of R1234yf

0

25
50
75
100
Concentration[vol%]Fig. 3.4.6 Maximum pressure in the engine
versus the concentration of R134a(c) Results of Experiment 3
Fig. 3.4.7 shows the results of an analysis of exhaust gas by FT/IR when the gaseous mixture of the air, R1234yf,
and lubricant oil was compressed and combustion occurred. When the combustion of the gaseous mixture occurred,production of HF and COF 2 , which results from the decomposition and decreasing concentration of the refrigerant,
was observed. The formula for the chemical reaction between oxygen and R1234yf is shown below (JSRAE, 2013).
Production of HF and COF 2 was also observed with the other three refrigerants. In the case of R410A, theconcentration of R32 decreased particularly notably, indicating that the R32 combusted.

C 3 H 2 F4 +5O 2 → 2CO 2 + 2HF + COF2
2

Table 3.4.5 shows the absorbance of HF. The cause of the differences of HF concentration for each refrigerant is notrevealed.

Fig. 3.4.7 Infrared absorption spectrum of exhaust for R1234yf gas mixture
Table 3.4.5 HF absorbance for each refrigerant
Refrigerant

HF concentration [vol. %]R1234yf

0.361

R32

0.182

R410A

0.261

R134a

0.126

3.4.4 Conclusions Concerning the Risk of Diesel Combustion during Pump-Down of a Heat
Pump
Fig. 3.4.8 shows a schematic diagram of the concentration of refrigerant and the maximum pressure due tocompression of a gaseous mixture of air, refrigerant, and lubricant oil. The concentration of the refrigerant is plottedon the horizontal axis, and the maximum pressure is plotted on the vertical axis. In the range of high refrigerant
concentrations, no combustion occurred with any of the refrigerants, and the maximum pressure increased as the35concentration of the refrigerant decreased. In the range of low refrigerant concentrations, self-ignition of the
lubricant oil occurred first. With a refrigerant of high flammability, the maximum pressure is higher because of
combustion of the refrigerant itself. With a refrigerant of low flammability, on the other hand, the refrigerant itself
does not combust and the maximum pressure remains low.
The results for R1234yf, R32, and R410A were similar to those for the high-flammability refrigerant discussed
above. The results for R134a were similar to those for the low-flammability refrigerant. Regardless of whether or
not combustion occurred, HF and COF 2 were detected in the exhaust gas for all of the refrigerant, which indicatesthat the refrigerants reacted in some way.

Pressure[-]

3
2
1
0
0

25
50
75
100
Concentration of refrigerant[vol%]Combustion range (high-flammable refrigerant)
Combustion range (low-flammable refrigerant)
Non-combustion range
Fig. 3.4.8 Schematic diagram of the relationship between the maximum pressure and the concentration of refrigerant

References
Japan Fluorocarbon Manufacturers Association (JFMA) ed., 2012, List of CFCs, HCFCs and fluorocarbons’environmental and safety data, JFMA, http://www.jfma.org/atabase/table.html (in Japanese)
The Japan Society of Refrigerating and Air Conditioning Engineers (JSRAE), 2013, Risk Assessment of Mildly
Flammable Refrigerants 2012 Progress Report, JSRAE, http://www.jsrae.or.jp/info/2012progress_report_e.pdf
Kataoka, O., Yoshizawa, M., Ohnishi, H., and Ishida, S., 1996, Flammability evaluation of HFC-32 and HFC32/134a under practical operating conditions, Proceedings of the International Refrigeration Conference,
Purdue, USA, July 1996.
National Institute of Standards and Technology (NIST), 2011, Chemistry WebBook, NIST,
http://webbook.nist.gov/chemistry/
Pacific Northwest National Laboratory (PNNL), 2012, Northwest-Infrared,
https://secure2.pnl.gov/nsd/nsd.nsf/Welcome
Takizawa, K., Tokuhashi, K., Kondo, S., and Nagai, H., 2011. Flammability evaluation of R-1234yf and R1234ze(E), Proceedings of the 49th Combustion Symposium, 146-147, Yokohama, Japan (in Japanese).
Takizawa, K., 2012. Flammability properties of 2L refrigerants, Proceedings of the International Symposium on
New Refrigerants and Environmental Technology 2012, Kobe, Japan.
Tokyo Metropolitan Association of Refrigeranting Air Conditionig Equipment (TRK), Technical Report (inJapanese).
Tokyo Metropolitan Government, 2012. The report on an accident caused by a technical error during removal
operation of RAC, (in Japanese), https://www.shouhiseikatu.metro.tokyo.jp/attention/aircon.html

36

4. Progress at Kyushu University
4.1 Introduction
The research group is working on the following subjects under the NED project titles “Development of low-GWP
refrigerants suitable for vapor compression heat pump systems.”
1. Focusing on a new refrigerant, HFO-1234ze(Z), for which data are not yet available in the public domain, inorder to clarify its chemical characteristics including safety, thermodynamic, and transport properties; heattransfer characteristics; and performance of the basic heat pump cycle.
2. To explore and select a low-GWP refrigerant mixture, which is composed of HFO refrigerants including HFO1234ze(Z), HFC refrigerants, and natural refrigerants, for use in commercial air conditioning systems. To
clarify the thermodynamic and transport properties, heat transfer characteristics, and performance of the basic
heat pump cycle for the low-GWP refrigerant mixture.
3. To build a fundamental technology for the practical use of the low-GWP refrigerant mixture.
The results of thermodynamic and transport property measurements, proposal of the equation of state (EOS), andheat transfer experiment on HFO-1234ze(Z) are mentioned in this report. Additionally, with the selected refrigerant
mixture HFO-1234ze(E)/HFC-32/CO2, validation of the mixture model, as well as the results of the experiment onheat transfer and performance of a basic heat pump cycle are presented.

4.2 Thermodynamic Properties and Heat Transfer Characteristics of
HFO-1234ze(Z)4.2.1 Thermophysical properties of HFO-1234ze(Z)By an isochoric method, PρT properties and saturated vapor pressure of HFO-1234ze(Z) were measured. Ten values
for the density varying from 223.7 to 833.2 kg/m3 were obtained in the temperature range 403–423.3 K; while 19
values for vapor pressure were obtained in the temperature range 310–420 K and pressure range 263–3333 kPa. In
addition, 263 values for the PρT property along with 11 isochoric curves were obtained in the temperature range
310–440 K and pressure range 263 kPa–6 MPa.
By the visual observation of meniscus disappearance taking into consideration the intensity of critical opalescence,as well as from the break point of isochors, the vapor-liquid coexistence curve and critical parameters were
determined as follows:
Tc = 423.27 ± 0.03
c = 470 ± 5
Pc = 3533 ± 10

K
kg/m3
kPa

(4.1)
(4.2)
(4.3)

A new equation of state was developed for HFO-1234ze(Z), which provides better representation of experimental
data than the preliminary equation. Fig. 4.2 is the newly obtained P-h diagram. The new equation is valid fortemperatures from 273 K to 430 K and for pressures up to 6 MPa with an uncertainty of 0.15% for vapor pressures,
0.4% for vapor densities, 0.2% for liquid densities, and 0.05% for the vapor-phase sound speeds. The equation
exhibits reasonable extrapolation behavior in regions away from the valid range. Fig. 4.3 shows deviations inexperimental vapor pressures from calculated values with the equation of state. In Fig 4.2, the vapor-liquid
coexisting curve obtained from the equation is plotted using experimental data for the saturated liquid and vapor
densities. These figures suggest that the equation of state developed in this work has sufficient accuracy for mosttechnical applications.
The FLD file for REFPROP based on the developed equation of state is available from the NIST website.

37

HFO-1234ze(Z)
6000

P/kPa

4000

ρ ≒ 1002 kg/m3 3
ρ ≒ 901 kg/m 3
ρ ≒ 752 kg/m 3
ρ ≒ 670 kg/m 3
ρ ≒ 570 kg/m 3
ρ ≒ 470 kg/m 3
ρ ≒ 340 kg/m 3
ρ ≒ 240 kg/m 3
ρ ≒ 140 kg/m 3
ρ ≒ 106 kg/m3
ρ ≒ 45 kg/m

2000

0
300

350

400

450

T/K

Fig. 4.1 PT properties of HFO-1234ze(Z)Fig. 4.2 Ph diagram for HFO-1234ze(Z)
440

T (K)

100(ps,exp / ps,cal −1)

1.0
0.0

Sa
tur
ate
d

380
360
340

−1.0
−2.0
250

id
liqu
ed
rat

2.0

tu
Sa

400

va
po
r

420

320

300

350

T (K)

400

Tc

300
0

450

Fig. 4.3 Deviations in experimental vapor pressuresfrom values calculated using the equation of state:(□●) Kayukawa et al. (2012)(×) Higashi et al. (2013)(▷) Tanaka et al. (2013)(■＋) Fedele et al. (2013)(—) Vapor pressure correlation by Higashi et al.
(2013)

200

400

600

−3

 (kg·m )

800

1000

1200

Fig. 4.4 Vapor-liquid coexistence curve for HFO1234ze(Z):(●) Kayukawa et al. (2012)(×) Higashi et al. (2013)(◎) Raabe (2012)(▷) Tanaka et al. (2013)(—) Equation of state(○) Critical parameters calculated from the equationof state (470.615 kg/m3, 423.27 K)

4.2.2 Transport properties of HFO-1234ze(Z)This year, the thermal conductivity of HFO-1234ze(Z) vapors was measured, as was done for the saturated liquids of
HFO-1234ze(Z), HFO-1234ze(E), and HFC-32 reported last year. Moreover, the liquid viscosity of HFO-1234ze(E)and HFO-1234ze(Z) was measured.
The thermal conductivity of HFO-1234ze(Z) was measured by a transient hot-wire method, in which two Pt wires(15 mm) of different lengths were used under isopycnic conditions. Figs. 4.5 (a) and (b) show the measurement
conditions and measurement results, respectively. In Fig. 4.5, the lines for HFC-32 and HFO-1234ze(E) show values
calculated using REFPROP9.1, and the line for HFO-1234ze(Z) denotes a correlation obtained from the extended
corresponding states (ECS) model coupled with the equation of state developed by Akasaka et al. (2013). The
calculated and measured values of vapor thermal conductivity show excellent agreement.

38

Figs. 4.6 (a) and (b) respectively show the measurement conditions and results for HFO-1234ze(E) liquid viscosity.
Figs. 4.7 (a) and (b) show measurement conditions and results for HFO-1234ze(Z). The liquid viscosities were
measured by the capillary method in which two capillary tubes of different lengths were used to cancel the endeffects, under isobaric conditions corresponding to the saturation temperatures of 99.5, 90, and 70 °C. The lines
denote the values calculated using REFPROP9.1 and the ECS model of Akasaka et al. (2013). The liquid viscosities
of both HFO-1234ze(E) and HFO-1234ze(Z) drastically decrease with increasing temperature. At a given
temperature, the viscosity of HFO-1234ze(Z) is notably higher than that of HFO-1234ze(E). These tendencies are
qualitatively identical to those of the predicted values; in particular, the predicted viscosity of HFO-1234ze(E)agrees well with the measured viscosity. On the basis of measured viscosity, the ECS model will be modified for
HFO-1234ze(Z).
Exp.Data
R32
R1234ze(Z)R1234ze(E)Pressure [MPa]

5
4

VLE

3
2

R32
R1234ze(Z)R1234ze(E)

1
0
280

300
320
340
Temperature [K]

360

20

Thermal conductivity [mW/m・K]

6

Exp.Data
HFC-32
HFO-1234ze(Z)HFO-1234ze(E)18
16

REFPROPVer9.1
HFC-32
HFO-1234ze(E)14

ECS model
HFO-1234ze(Z)

12
10
280

300
320
340
Temperature [K]360(a) Measurement conditions(b) Measurement results
Fig. 4.5 Thermal conductivity of HFO-1234ze(Z) vapors
HFO-1234ze(E)3.02MPa
2.49MPa
1.61MPa
VLE

Pressure [MPa]Liquid
3
2
1

Gas

0
280

300

320
340
Temperature [K]

360

250
Viscosity [Pa·s]

4200

REFPROP Ver9.1
3.02MPa
2.49MPa
1.61MPa

150
100
280

380

HFC-1234ze(E)Exp.Data
3.02MPa
2.49MPa
1.61MPa

300

320
340
Temperature [K]360(a) Measurement conditions(b) Measurement results
Fig. 4.6 Liquid viscosity of HFO-1234ze(E)HFO-1234ze(E)3.02MPa
2.49MPa
1.61MPa
VLE

Pressure [MPa]Liquid
3
2
1
0
280

Gas
300

320
340
Temperature [K]360

HFO-1234ze(Z)Exp.Data
1.35MPa
1.08MPa
0.67MPa360
Viscosity [Pa·s]

4

320
280

200
160
280

380

ECS model
1.35MPa
1.08MPa
0.67MPa

240

300

320
340
Temperature[K]360(a) Measurement conditions(b) Measurement results
Fig. 4.7 Liquid viscosity of HFO-1234ze(Z)4.2.3 Heat transfer characteristics of HFO-1234ze(Z)(a) Heat transfer in horizontal microfin tubes
The evaporation and condensation heat transfer coefficients (HTCs) and pressure gradients of HFO-1234ze(Z)flowing in a microfin tube were measured using a vapor compression cycle. The test tube used was a copper tube
with an outer diameter of 6.08 mm, a fin root diameter of 5.49 mm, and an equivalent inner diameter of 5.34 mm,

39

with 48 helical inner microfins. The fin height, lead angle, and surface enlargement were respectively 0.255 mm,
20.1°, and 2.24. The test section was divided into four subsections. The pressure gradients at intervals of 554 mm
and HTCs over the 414 mm active heat transfer length were measured.
Fig. 4.8 shows the HTCs during the evaporation and condensation of HFO-1234ze(Z). The experiments were carriedout at a mass velocity of 200 kg/(m2s), a heat flax of 10 kW/m2, and saturation temperatures of 30 and 65 °C forevaporation and condensation, respectively. The results for HFC-134a and HFO-1234ze(E) are plotted in Fig. 4.8.
The lines show the HTCs predicted using the correlation of Mori et al. (2002) and Cavallini et al. (2009). For
evaporation, the HTCs of HFO-1234ze(Z) are lower than those of HFC-134a and HFO-1234ze(E) at vapor qualities
lower than 0.3. However, except that region, the HTCs of HFO-1234ze(Z) are somewhat higher than those of theother two refrigerants. These characteristics were well predicted using the FLD file provided by Akasaka et al.
(2013) by the existing correlations.
Figure 4.9 shows the pressure gradients of HFC-134a, HFO-1234ze(E), and HFO-1234ze(Z) during evaporation andcondensation under the same conditions as those indicated in Fig. 4.8. The lines show pressure gradients predictedusing the correlation of Kubota et al. (2001) and Yonemoto-Koyama (2007). The pressure gradients of HFO1234ze(Z) are larger than those of HFC-134a and HFO-1234ze(E). The main cause for this is the higher vapor
velocity of HFO-1234ze(Z) due to the lower vapor density. From the same reason, the pressure gradients incondensation at the saturation temperature of 65 °C are approximately 1/3 of those at 30 °C. As reducedpressure/temperature increases, the vapor density increases; thus, the pressure gradients decreases as vapor velocity
decreases. These characteristics are well predicted by the existing correlations.
30

25
20

Evaporation
at 30 oC, 200 kg m-2s-1, 10 kW m-2

Condensation
at 65 oC, 200 kg m-2s-1, 10 kW m-2

R134a
R1234ze(E)R1234ze(Z)R134a
R1234ze(E)R1234ze(Z)Mori et al. (2002)

Cavallini et al. (2009)25
20

Evaporation
at 30 oC, 200 kg m-2s-1, 10 kW m-2

Condensation
at 65 oC, 200 kg m-2s-1, 10 kW m-2
R134a
R1234ze(E)R1234ze(Z)R134a
R1234ze(E)R1234ze(Z)Yonemoto-Koyama (2007)

Kubota et al. (2001)

15

15

10

10
5
0

Pressure gradient P/Z [kPa m-1]

HTC  [kW m -2K-1]

30

0.2
0.4
0.6
0.8
Vapor quality, x [ - ]

10

0.2
0.4
0.6
0.8
Liquid quality, 1-x [ - ]1Fig. 4.8 HTC in horizontal microfin tube

5
0

0.2
0.4
0.6
0.8
Vapor quality, x [ - ]

10

0.2
0.4
0.6
0.8
Liquid quality, 1-x [ - ]1Fig. 4.9 Pressure gradient in horizontal microfin tube(b) Heat transfer on horizontal smooth tubes
The condensation and pool boiling HTCs on a horizontal plane tube were measured by a test loop with natural
circulation. The outer diameter of the test tube and heat transfer length were 19.12 mm and 400 mm, respectively.
Fig. 4.10 shows variations in condensation HTCs against the degree of wall subcool for HFC-134a, HFO-1234ze(E),and HFO-1234ze(Z). The symbols denote experimental HTCs, with vertical and horizontal bars indicating themeasurement uncertainty in HTC and degree of subcool. The solid and dashed lines denote theoretical HTCs
predicted using the Nusselt theory (1916). The condensation HTC of HFC-134, in which the thermodynamic
properties are most authorized, agrees with the theoretical HTC within the measurement uncertainty. From thisresult, the validation of this experimental method is demonstrated.
The experimental values of HFO-1234ze(E) and HFO-1234ze(Z), as shown respectively in Figs. 4.10(b) and (c),agreed with the theoretical values calculated using the FLD file provided by Akasaka et al. (2013) withinapproximately 10%. Among the tested refrigerants, the condensation HTC of HFO-1234ze(Z) was the highest,
followed by those of HFC-134a and HFO-1234ze(E). This order can be explained by the thermodynamic propertiesof the refrigerants. The liquid thermal conductivity and latent heat of HFC-134a and HFO-1234ze(Z) were 8–20%
and 6–24% higher than those of HFO-1234ze(E), respectively. The above-mentioned tendency could be precisely
predicted using the Nusselt theory (1916) by employing the provided FLD file.
Fig. 4.11 shows variations in pool boiling HTC against wall heat flux. The solid and dashed lines denote the values
calculated using the correlation of Stephan-Abdelsalam (1978) proposed for the pool boiling of other refrigerants.
The pool boiling HTC of HFO-1234ze(Z) is considerably lower than that of HFC-134a and HFO-1234ze(E). At thegiven saturation temperature, the reduced pressure of HFO-1234ze(Z) ranges from 0.02 to 0.15. This value isnotably lower than those of the others, and thus, the surface tension of HFO-1234ze(Z) is larger. For balancing thesurface tension, the bubble departure diameter becomes larger and more wall superheat is required for boiling.
Figs. 4.12(a)–(c) show the pictures of nucleate boiling on the wall surface of HFC-134a, HFO-1234ze(E), and HFO-

40

1234ze(Z) at a saturation temperature of 20 °C and a heat flux of 15 kW/m2. Fig. 4.12(d) shows the picture of HFO1234ze(Z) at a saturation temperature of 40 °C and a heat flux of 15 kW/m2. The bubble diameter of HFO1234ze(Z), as shown in Fig. 4.12(c), is clearly larger than that of other refrigerants (Figs. 4.12(a) and (b)). By
contrast, the nucleation site density of HFO-1234ze(Z) is smaller than that of other refrigerants. Gaertner-Westwater(1960) remarked that the bubble departure diameter increases with decreasing nucleation site density. Therefore, thepool boiling HTC of HFO-1234ze(Z) is low mainly due to the smaller nucleation site density. This also decreases
the pool boiling HTC.
Nusselt Theory5 [kW m–2 K–1]

Tsat = 20 °C
Tsat = 30 °C
Tsat = 35 °C
Tsat = 40 °C

20 °C

4
3
2

40 °C

1
0.5

1

5 10
Tsat–Twall [K]Tsat = 20 °C
Tsat = 30 °C
Tsat = 40 °C
Tsat = 50 °C

0.5(a) R134a

5 10
Tsat–Twall [K]0.51(b) R1234ze(E)

5 10Tsat–Twall [K](c) R1234ze(Z)Fig. 4.10 Condensation HTC on horizontal smooth tube
Stephan–Abdelsalam50 [kW m–2 K–1]

1

Tsat = 20 °C
Tsat = 30 °C
Tsat = 40 °C
Tsat = 50 °C
Tsat = 60 °C

Tsat = 10 °C
Tsat = 20 °C
Tsat = 30 °C
Tsat = 40 °C

10
5Tsat = 5 °C
Tsat = 10 °C
Tsat = 20 °C
Tsat = 30 °C
Tsat = 40 °C
Tsat = 50 °C

Tsat = 5 °C
Tsat = 10 °C
Tsat = 20 °C
Tsat = 30 °C
Tsat = 40 °C
Tsat = 50 °C
Tsat = 60 °C

50 °C

1
0.5
5 °C

0.1
0.1

0.5 1
5 10
–2
qwall [kW m ](a) R134a

50100 0.1

0.5 1
5 10
–2
qwall [kW m ]50100 0.1(b) R1234ze(E)

0.5 1
5 10
–2
qwall [kW m ]50100(C) R1234ze(Z)Fig. 4.11 Pool boiling HTC on horizontal smooth tube

（ a） R134a（ b） R1234ze(E)（ c） R1234ze(Z)（ d） R1234ze(Z)Tsat = 20 °C
Tsat = 20 °C
Tsat = 20 °C
Tsat = 40 °C
qwall = 15 kW/m2
qwall = 15 kW/m2
qwall = 15 kW/m2
qwall = 15 kW/m2
Fig. 4.12 Nucleate boiling sites of R134a, R1234ze(E), and HFO-1234ze(Z)4.2.4 Cycle performance of HFO-1234ze(Z)To find the optimum temperature range for the heat source, drop-in experiments and numerical analysis were carriedout for high-temperature applications of HFO-1234ze(E) and HFO- 1234ze(Z). A test loop made to measure the41

cycle performance by the drop-in experiment mainly consisted of a hermetic compressor, a solenoid expansion valve,
and two double-tube-type heat exchangers with counter-flow configurations. Table 4.1 lists the test conditions
employed in the drop-in experiments for HFO-1234ze(E), HFO-1234ze(Z), and HFO- 1234ze(E)/HFC-32 (95/5
mass%).
Fig. 4.13 presents the experimental results for COP and heating load. Under the conditions listed in Table 4.1, the
COP and heating load of HFO-1234ze(E) are clearly higher than those of HFO-1234ze(Z). Adding HFC-32 (5mass%) to HFO-1234ze(E) somewhat improves the COP and heating capacity of both. Although the COP of HFO1234ze(Z) is relatively high at a smaller heating load, this drastically decreases with increasing heating load. Thissuggests that HFO-1234ze(Z) is most likely suitable for a higher temperature range than the test condition.
Fig. 4.14 shows the breakdown of the irreversible losses and COP obtained by a numerical analysis at condensation
temperatures of 75, 105, and 125 °C, and a heating load of 1.8 kW. The calculation method is validated from the factthat the calculated COPs of HFO-1234ze(E) and HFO-1234ze(Z) at condensation temperature of 75 °C are almost
identical to the experimental results shown in Fig. 4.13. The irreversible loss in the compressor and the irreversible
loss caused by a pressure drop for HFO-1234ze(Z) are remarkably higher than those for HFO-1234ze(E) at 75 °C
because of an insufficient volumetric capacity of HFO-1234ze(Z). As condensation temperature increases from 75 to
105 °C and then to 125 °C, the irreversible losses in the compressor and pressure drop decrease and the COP of
HFO-1234ze(Z) increases. This suggests that HFO-1234ze(Z) is beneficial for rather high-temperature applications
than air conditioners.
Table 4.1 Conditions for drop-in experiment
Water Temp.

Cond.
Eva.

50→75

[◦C]

45→39

Degree of superheat[K]

3Heat transfer rate[kW]

1.2–2.4
COP=5.4
Ltotal=231.4

L [W]

250

Irreversible loss

COPcycle [-]8

R1234ze(E)R1234ze(Z)7 R1234ze(E)/R32 (95/5mass%)

200

COP=6.2
Ltotal=181.4
LP

Heating 1.8 kW

COP=6.3
Ltotal=188.0

COP=6.6
Ltotal=177.2

150
LCOMP

100

6

LEXP
LEVA

50
LCOND

5
1

1.5

2

2.5

0

Q [kW]

Fig. 4.13 Drop-in experiment results for COP

R1234ze(E)R1234ze(Z)R1234ze(Z)R1234ze(Z)at 75 oC
at 75 oC
at 105 oC
at 125 oC

Fig. 4.14 Break down of irreversible loss ofvarious condensing temperatures obtained bynumerical calculations

4.3 Thermodynamic Properties and Heat Transfer Characteristics of
Low-GWP Refrigerant Mixtures
To evaluate the thermodynamic performance of ternary HFO-1234ze(E)/HFC-32/CO2 mixtures, measurement of theheat transfer coefficient and drop-in experiment were conducted this year. As the first step, last year, two massfractions of HFO-1234ze(E)/HFC-32/CO2 were selected from a brief assessment. Fig. 4.15 illustrates the assessment
results for the thermodynamic characteristics. The lines in the ternary diagram represent the contours of GWP,
temperature glide, the COP ratio, and volumetric capacity ratios relative to HFC-410A. On the basis of the criteria

42listed in Table 4.2, two compositions were selected. The ternary blend “A” (HFO-1234ze(E)/HFC-32/CO2, 53/43/4
mass%) was used to achieve a GWP just below 300. The ternary blend “B” (HFO-1234ze(E)/HFC-32/CO2, 262/29/9
mass%) was used to achieve a GWP just below 200. In Fig. 4.15, the red and blue symbols indicate the selected
ternary blend A and B, respectively.
R744

Table 4.2 Criteria for refrigerant selection
Condition

A

B

GWP

<300

<200

Temperature glide

<10 K

<15 K

Volumetric capacity ratio>0.8

COP ratio

>1.0

10K
15K
200
300
0.8

1.0

R1234ze(E)

0.95
1.00
R32

GWP
Temp. glide
COP ratioVol. capacity ratio

Fig. 4.15 Thermodynamic assessment results.
(Calculation conditions: condensation temp. of 30 °C,
subcool of 0 K, evaporation temp. of -3 °C, superheatof 3 K, and compressor efficiency of 0.85)

4.3.1 Thermophysical properties of low-GWP refrigerant mixture
As with HFO-1234ze(Z), the thermophysical properties were measured for the selected ternary mixture 54 mass%
HFO-1234ze(E) + 43 mass% HFC-32 + 3 mass% CO2.
By an isochoric method, PρT properties and saturated vapor pressure of this mixture were measured. Thirteen values
for the density varying from 240.6 to 807.5 kg/m3 were obtained in the temperature range 345.9–363.1 K. Further,
101 values for PρT properties along the 6 isochoric curves were obtained in the temperature range 310–385 K,
density range 181–666 kg/m3, and pressure range 1784 kPa–6.9 MPa.
From the visual observation of meniscus disappearance, the break point of isochors, the vapor-liquid coexistence
curve, and the critical parameters were determined as follows:
Tc = 361.83 ± 0.03

c = 466 ± 5

Pc = 5394 ± 10

K
kg/m3
kPa

(4.4)
(4.5)
(4.6)

A mixture model was presented for the ternary HFO-1234ze(E)/HFC-32/CO2 mixture. The multifluid approximation
explicit in Helmholtz free energy forms the basis of the model presented in this work. The approximation represents
total interaction between molecules in the ternary mixtures as the sum of each binary pair interaction. In this work, a
new binary model for the binary pair of HFO-1234ze(E) /HFC-32 was combined with available models for the othertwo binary pairs.
Fig. 18 shows the vapor-liquid coexistence curve obtained from the new mixture model for HFO-1234ze(E)/HFC-32,
as well as from the experimental data. Although a slightly different behavior was observed for the saturated vapor
densities, the model showed good representation of the saturated liquid densities and critical parameters. Fig. 19
shows the vapor-liquid coexistence curve obtained using the ternary mixture model incorporating the new binarymodel for HFO-1234ze(E)/HFC-32. Since the ternary model did not use additional parameters for ternary mixtures,the curve was completely predictive. In spite of this, the experimental saturated liquid densities were well
represented by the model, and the calculated critical parameters almost corresponded to experimental values.

43

390

5 4 %HFO- 1 2 3 4 z e( E) + 4 3 %HFC- 3 2 + 3 %CO2
HFO-1 2 3 4 z e( E)

7000

380

6000
( 5 4 /4 3 /3 )( 1 2 3 4 ze( E) + 3 2 + CO2 )5000

P / kPa

T/ K

370

360

350
HFC-3 2

1 8 0 kg /m 3
2 5 0 kg /m 3
3 7 0 kg /m 3
4 7 1 kg /m 3
5 7 1 kg /m 3
6 6 6 kg /m 3
R 32
R 1 2 3 4 ze( E)
Critical Point

4000

3000

340

2000
330
100

200

300

400

500

600

 / kg m

700

800

1000
300

900

-3

320

340

360

380

400

T/K

Fig. 4.16 T- diagram for HFO-1234ze(E)/HFC32/CO2

Fig. 4.17 P-T diagram for HFO-1234ze(E)/HFC32/CO2.
370
R32/1234ze(E)/744 = 43/54/3 mass%

390
R1234ze(E)

365

380
R1234ze(E)/R32 = 75/25 mass%

370

360
T (K)

T (K)

50/50 mass %360
25/75 mass%

355

R32

350

Critical point

350
Critical point
Experimental
Calculated

340

330
100

Experimental
Calculated

200

300

400

500 −3 600
 (kg·m )

700

800

345
100

900

200

300

400

500 −3 600

 (kg·m )

700

800

900

Fig. 4.19 Vapor-liquid coexistence curve for HFO1234ze(Z)/HFC-32/CO2:(□■) Experimental data obtained in this project(—) Ternary mixture model for HFO-1234ze(Z)/HFC-32/CO2.

Fig. 4.18 Vapor-liquid coexistence curve for HFO1234ze(Z)/HFC-32:(▲□●) Experimental data obtained in this project(—) Binary mixture model for HFO-1234ze(Z)/HFC32.

4.3.2 Heat transfer characteristics of low-GWP refrigerant mixtures(a) Heat transfer in horizontal microfin tubes
HTCs and pressure gradients in a microfin tube were measured for a low-GWP refrigerant mixture as well as for
HFO-1234ze(Z). The experiments were carried out at average saturation temperatures (the average of dew point andboiling point) of 10 and 40 °C for evaporation and condensation, respectively. These are typical operation conditions
for air conditioners. The test refrigerants were: a binary mixture (HFO-1234ze(E)/HFC-32: 70/30 mass%) and aternary mixture (HFO-1234ze(E)/HFC-32/CO2: 62/39/9 mass%) with a GWP of 200, as well as a binary mixture(HFO-1234ze(E)/HFC-32: 60/40 mass%) and a ternary mixture (HFO-1234ze(E) /HFC-32/CO2: 53/43/4 mass%)with a GWP of 300. The circulation composition was measured at the outlet of the sub-cooler. With the circulation

44

HTC  [kW m-2K-1]

15

10

G = 200 kg m -2s-1, q = 10 kW m-2s-1(Tbubble+Tdew)/2 = 10 °C

G = 200 kg m-2s-1, q = 10 kW m-2s-1(Tbubble+Tdew)/2 = 40 °C

R744/R32/R1234ze(E)0/30/70 mass% (GWP = 207)
9/29/62 mass% (GWP = 200)
0/40/60 mass% (GWP = 274)
4/43/53 mass% (GWP = 293)

R744/R32/R1234ze(E)0/30/70 mass% (GWP = 207)
9/29/62 mass% (GWP = 200)
0/40/60 mass% (GWP = 274)
4/43/53 mass% (GWP = 293)

Pressure gradient P/Z [kPa m-1]

composition, the refrigerant temperature and vapor quality were calculated using mixing parameters (Akasaka,2013), which were optimized on the basis of the measurement data of Higashi et al. (2013) and others.
Fig. 20 shows the measured evaporation and condensation HTCs. The HTCs of refrigerant mixtures are significantly
lower than those of single components. This is a typical behavior of mass transfer resistance caused by the volatility
difference between the components.
As it has already been remarked in previous studies, the resistance decreases HTC more when the temperature glide
is larger, the mole fraction difference between the liquid and vapor of each component is larger, and the vapor
velocity is lower. The experimental condensation HTCs of the ternary mixture (HFO-1234ze(E)/HFC-32/CO2:
62/39/9 mass%) that had the largest temperature glide was the lowest among the tested refrigerants. Thus, thetendency of condensation HTCs was qualitatively identical to those reported previously. On the other hand, in thecase of evaporation, there was no significant difference between each refrigerant because the HTCs of all the tested
refrigerants were significantly low. Nevertheless, the HTC of (HFO-1234ze(E)/HFC-32/CO2: 62/39/9 mass%)
having the highest mass fraction of CO2 was the lowest because of the lower vapor velocity due to higher vapor
density.
Fig. 20 shows the measured pressure gradients. In contrast to HTCs, these pressure gradients are comparable tothose of single components. The evaporation pressure gradient of refrigerants contains more CO2 and HFC-32 tends
to be smaller, owing to their higher vapor density. In the case of condensation, pressure gradients are smaller thanthose of evaporation, and the difference between each refrigerant is relatively small.

5

0

0.2
0.4
0.6
0.8
Vapour quality, x [ - ]

10

0.2
0.4
0.6
0.8
Liquid quality, 1-x [ - ]15Fig. 4.20 HTC of low-GWP refrigerant
mixturesR744/R32/R1234ze(E)0/30/70 mass% (GWP = 207)
9/29/62 mass% (GWP = 200)
0/40/60 mass% (GWP = 274)
4/43/53 mass% (GWP = 293)

10

5

0

1

G = 200 kg m -2s-1, q = 10 kW m-2s-1(Tbubble+Tdew)/2 = 40 °C

G = 200 kg m-2s-1, q = 10 kW m-2s-1(Tbubble+Tdew)/2 = 10 °C

0.2
0.4
0.6
0.8
Vapour quality, x [ - ]

1 0

0.2
0.4
0.6
0.8
Liquid quality, 1-x [ - ]1Fig. 4.21 Pressure gradient of low-GWP
refrigerant mixtures(b) Heat transfer in plate heat exchangers
The flow pattern of air-water flow was visualized; further, the void fraction was measured using a transparent
acrylic plate having herringbone grooves. Then, the HTC of HFO-1234ze(E) in a stainless steel plate heat exchanger
having herringbone grooves, which was placed in a pump loop, was measured. Of the stainless test plate with athickness of 10 mm, on the side surfaces of both the heat source and refrigerant, 5 grooves were made for inserting
thermocouples at 22.4 mm intervals. The local heat fluxes at the points, where surface temperatures of the heatsource and refrigerant sides were measured, were determined by considering one-dimensional steady state heat
conduction over the test plate. From the local heat fluxes and the measured surface temperatures, the HTCs wereobtained at condensation temperatures from 35 to 40 °C, evaporation temperatures from 5 to 10 °C, and a mass
velocity of 10 kg/(m2s).
Figs. 22 (a) and (b) plot the surface temperature distribution and local HTC during condensation. As condensation
proceeds, the temperature difference between the right and left increases and the local HTC monotonically decreases.
The local HTC on the left side, where refrigerant speed is most likely higher near the inlet/outlet, is slightly higher
than that on the right side.
Figs. 23 (a) and (b) plot the surface temperature and local HTC during the evaporation process, similar to that forcondensation. As the vapor quality increases, the right-side local HTC decreases. Probably, this is caused by thestrong misdistribution of the refrigerant flow. The left-side HTC, which is close to the inlet/outlet and thin liquidfilm could be formed by the high-speed vapor flow, is relatively higher; moreover, the local HTC is decreased by the
thicker liquid film because of the slow vapor flow.

4.3.3 Cycle performance of low-GWP refrigerant mixtures
To evaluate the cycle performance of the ternary mixture HFO-1234ze(E)/HFC-32/ CO2 and HFO-1234ze(Z), drop-45

Tback,left [℃]
Tback,right [℃]

32
28
24
20
Tsat = 37.3 [℃]
2
12 G = 10.1 [kg/m s]
20

40

80

100

hback,left
hback,right

2000
1600
1200

60

LHTC [W/(m K)]
hfront,lefthfront,right

2400

16

0

2

2800

Tback,left [℃]
Tback,right [℃]120

Tsat = 37.3 [℃]2
G = 10.1 [kg/m s]00.2

Distance z [mm]

0.4

0.6

0.8

1.0

(a) Wall temperature distribution (b) Local HTC
Fig. 4.22 Condensation HTC

Heat source temp. [°C]

15 → 920 → 10

Heat sink temp. [°C]
Degree of superheat [K]Heat transfer rate [kW]20 → 45

30 → 453
1.6 ~ 2.6 1.4 ~ 2.4

40
36

Refrigerant side
Tfront,left [℃]
Tfront,right [℃]
Water side
Tfront,left [℃]
Tfront,right [℃]2

Tback,left [℃]
Tback,right [℃]
Tback,left [℃]
Tback,right [℃]Tsat = 8.3 [℃]
G = 9.1 [kg/m2s]

32
28
24

2000 LHTC [W/(m K)]
hfront,lefthfront,right1800

hback,left
hback,right

1600
1400
1200
1000

20

Tsat = 8.3 [℃]

2

16
0

20

40

60

80

100

120

Distance z [mm]Wetness (1- x) [ - ]Table 4.3 Conditions for drop-in experimentHeating Cooling

44

LHTC hx [W/m2K]

36

Refrigerant side
Tfront,left [℃]
Tfront,right [℃]
Water side
Tfront,left [℃]
Tfront,right [℃]

Wall temperature profile Tx [℃]

40

2

44

LHTC hx [W/m K]

Wall temperature profile Tx [℃]in experiment was conducted. The properties of refrigerant mixtures were evaluated at the circulation composition
that was measured at the subcooler outlet. Table 4.3 lists the test conditions for heating and cooling modes. Table
4.4 lists the test refrigerants. Test refrigerants were ternary mixtures (HFO-1234ze(E)/HFC-32/ CO2: 53/43/4 mass%
and 62/29/9 mass%), binary mixtures (HFO-1234ze(E)/HFC-32: 57/43 mass% and 72/28 mass%), and HFC-410A
as the conventional refrigerant. The compositions of the binary mixtures were determined from the criteria at a GWP
of 300 and 200.
Fig. 24 presents the experimental results for COP and heating/cooling load. In general, the COP decreases withincreasing heating/cooling load because the irreversible loss increases with increasing mass flow rate andcompression ratio. The COPs of the binary and ternary mixtures with a GWP of 200 are equivalent to or lower thanthat of HFC-410A. In the case of the binary mixture with a GWP of 200, compared with HFC-410A, irreversible
losses of compressor and pressure drop are supposed to be large because of the smaller volumetric capacity. In thecase of the ternary mixture with a GWP of 200, irreversible loss in the evaporator is larger than that in the case of
HFC-410A because of the very larger temperature glide that is unmatched to the distribution of water temperature.
On other hand, the COPs of the binary and ternary mixtures with a GWP of 300 are equivalent to or higher than thatof HFC-410A

800 G = 9.1 [kg/m s]
0
0.2
0.4

0.6

(a) Wall temperature distribution (b) Local HTC
Fig. 4.23 Evaporation HTC

Refrigerants
R-32/1234ze(E)Table 4.4 Test refrigerants
GWP Temp. glide [K]

43/57

28/72
R-744/32/1234ze(E) 4/43/53
9/29/62
R-410A

294

9.61

194
294
200
2088

11.90
13.67
21.59
0.11

COPh [-]

COPr [-]* At bulk temperature 10 °C
5.8
5.6
5.4
5.2
5
4.8
4.6
4.4
4.2
4 R410A R32/R1234ze(E) R744/R32/R1234ze(E)4/43/53
43/57
3.8
9/29/62
28/72
3.6
1.5
2
2.5
QEVA [kW]0.8

Quality x [ - ]

6.8
6.6
6.4
6.2
6
5.8
5.6
5.4
5.2
5 R410A R32/R1234ze(E) R744/R32/R1234ze(E)43/57
4/43/53
4.8
28/72
9/29/62
4.6
1.5
2
2.5
QCOND [kW](a) Cooling mode(b) Heating mode
Fig. 4.24 Results of drop-in experiments

46

1.0

4.4 Conclusions
In this paper, some of the NEDO-funded research carried out this year has been presented. From the research,
thermodynamic and transport properties of HFO-1234ze(Z) have been clarified. On the basis of precise
measurement results, an equation of state has been proposed. The FLD file built in the proposed equation of state
has been distributed by NIST, so that the properties of HFO-1234ze(Z) can be calculated using REFPROP 9.1.
Further, HFO- 1234ze(Z) heat transfer characteristics for some configurations have been reported.
Additionally, for the selected low-GWP refrigerant mixture, HFO-1234ze(E)/HFC-32/CO2, the measurement results
for thermodynamic properties and the validation of the mixing model have been reported. On the basis of theseverification results, the heat transfer characteristics and cycle performance have also been clarified.

References
Fedele, L., Di Nicola, G., Brown, J. S., Bobbo, S., Zilio, C., 2013. Measurements and Correlations of cis-1,3,3,3Tetrafluoroprop-1-ene (R1234ze(Z)) Saturation Pressure. To be published in Int. J. Thermophys.
Higashi, Y., Hayasaka, S., Ogiya, S., 2013. Measurements of PVT Properties, Vapor Pressures, and CriticalParameters for Low GWP Refrigerant R-1234ze(Z). In: Proceedings of Fourth Conference on Thermophysical
Properties and Transfer Processes of Refrigerants (Paper No. TP-018), Delft, The Netherlands.
Kayukawa, Y., Tanaka, K., Kano, Y., Fujita, Y., Akasaka, R., Higashi, Y., 2012. Experimental Evaluation of theFundamental Properties of Low-GWP Refrigerant HFO-1234ze(Z). In: Proceedings of the International
Symposium on New Refrigerants and Environmental Technology 2012, Kobe, Japan.
Raabe, G., 2012. Molecular Modeling of Fluoropropene Refrigerants. J. Phys. Chem. B, 116(19), 5744-5751.
Tanaka, K., Maruko, K., Fujimoto, Y., Tanaka, M., 2013. PVT Properties of R1234ze(Z). In: Proceedings of Fourth
Conference on Thermophysical Properties and Transfer Processes of Refrigerants (Paper No. TP-072), Delft,
The Netherlands.
Akasaka, R., Higashi, Y., Koyama, S., 2013. A Fundamental Equation of State for Low GWP Refrigerant HFO1234ze(Z). In: Proceedings of Fourth Conference on Thermophysical Properties and Transfer Processes ofRefrigerants (Paper No. TP-052), Delft, The Netherlands.
Mori, H., Yoshida, S., Koyama, S., Miyara, A., Momoki, S., 2002. Prediction of Heat Transfer Coefficients forRefrigerants Flowing in Horizontal Spirally Grooved Evaporator Tubes. In: Proc. 14th JSRAE Annual Conf.,
97-100 (in Japanese).
Cavallini, A., Del Col, D., Mancin, S., Rossetto, L., 2009, Condensation of Pure and Near-Azeotropic Refrigerants
in Microfin Tubes: A New Computational Procedure, Int. J. Refrig., vol. 32: p. 162-174.
Yonemoto R., Koyama S., 2007, Experimental Study on Condensation of Pure Refrigerants in Horizontal Micro-fin
Tubes: Proposal of Correlations for Heat Transfer Coefficient and Frictional Pressure Drop, Trans. JSRAE, 24(2), 139-148 (in Japanese).
Kubota, A., Uchida, M., Shikazono, N., 2001. Predicting Equations for Evaporation Pressure Drop Inside Horizontal
Smooth and Grooved Tubes, Trans. JSRAE, 18(4), 29-37 (in Japanese).
Nusselt, W., 1916, Die Oberflachenkondensation des wasserdampfes., Veeines Dtsch. Ingenieure, vol. 60, no. 27, pp.
541-546.
Stephan, K., Abdelsalam, M., 1978, Heat-Transfer Correlations for Natural Convection Boiling, Int. J. Heat Mass
Transfer., vol. 23, pp. 73-87.
Gaertner, R. F., Westwater, J. W., 1960. Population of Active Sites in Nucleate Boiling Heat Transfer, Chem. Eng.
Prog., Symp. Ser., vol. 56, no. 30.

47

5. Physical Hazard Evaluation of A2L Refrigerants Based on Several
Conceivable Accident Scenarios
5.1 Introduction
In Tokyo University of Science, Suwa, the project titled “Evaluation of Combustion and Explosion Hazards and Risk
Assessment on A2L Refrigerants for the Air-conditioning Systems” has been performed in cooperation with the
Research Institute for Safety and Sustainability (RISS), AIST. This project consists of two main subjects: (I)“Evaluation on fundamental properties of combustion and explosion on A2L refrigerants” (conducted by RISS, AIST)
and (II) “Physical hazard evaluation on A2L refrigerants based on several conceivable accident scenarios” (conductedby Tokyo University of Science, Suwa). We aim to perform a more detailed evaluation of the physical hazard of A2L
refrigerants on the basis of actual handling situations by collating the results obtained by each subject. In this report, we
describe the outline of the subject (II) conducted in FY2011-FY2013.

5.2 Assumed Accident scenarios
We assumed three main accident scenarios as shown
Deregulation for handling A2L refrigerants
in Figure 1. In this report, the following scenario
including sub-scenario are used.
The risk assessment based on the conceivable
accident scenario is indispensable(1) Scenario #1: A room air conditioning system
containingan
A2L
refrigerantisScenario #2
Scenario #3
Scenario #1
Service andA2L refrigerant used in
Simultaneously usedsimultaneously used with a fossil-fuelmaintenancea VRF systemwith a fossil-fuelsituations
heating system
heating system inside a general living space.
Smoking in a space containing the refrigerant(2) Scenario #2: An air conditioning system
Refrigerant leaks from a pinhole or a breakpoint
containing an A2L refrigerant is handled at
Refrigerant leaks into the device for servicing
the factory for the service and maintenance.
In this scenario, we focused on the following
Figure 1 Outline of the Physical hazard evaluation on A2L
three sub-scenarios.
refrigerants based on several conceivable accident scenarios(a) Sub-scenario (a): A serviceman uses a
conducted by Tokyo University of Science, Suwa.
portable lighter to smoke in a space inwhich an A2L refrigerant has leaked and accumulated,(b) Sub-scenario (b): An A2L refrigerant leaks from a fracture or pinhole in the pipes or hoses such as thatused to connect a car air conditioning system and a collection device,(c) Sub-scenario (c): An A2L refrigerant leaks inside a model device such as a collection device for theservice and maintenance.
(3) Scenario #3: An A2L refrigerant is used in the Variable Refrigerant Flow (VRF) system

5.3 Details of Physical Hazard Evaluation in Each Scenario
5.3.1 Scenario #1: Simultaneously used with a fossil-fuel heating system
5.3.1.1 Outline
In Scenario #1, we focused on two different utilization cases: an A2L refrigerant leaks from an air-conditioning system
into a general living space in which a fossil-fuel heating system has already been operating (Case (i)), and a fossil-fuelheating system operating in the general living space in which the leaked A2L refrigerant has already leaked andaccumulated (Case (ii)). Because the evaluation details of the physical hazards on this scenario was already describedin the previous progress report (Imamura et al, 2013) and reference (Imamura et al, 2012), only a summary is provided
in this report.

48

5.3.1.2 Experiment
A commercial room air conditioning system for an area of 6 Tatami mats (about 11 m2) was installed on the wall of anexperimental facility (cube, 2800 mm each side) where the center of the ventilation outlet was located 700 mm below
the ceiling and at the center in horizontal direction. Refrigerant was leaked in the downward vertical direction from theventilation outlet. In Case (i), a radiative oil stove (power: 2.4 kW, designed to heat 13 m2) and an oil fan heater(power: 3.2 kW, designed to heat 16 m2) were employed as the representative fossil-fuel heating system which had
already operated inside the general living space. In Case (ii), a ceramic heater (FPS1, Yarkar Ceramic Co., Ltd.) was
employed as the heating source instead of the fossil-fuel heating system because the heating source had to be controlled
remotely.
R1234yf, R32 and R410A were employed as the test refrigerants. The amount of leaked refrigerant was 800 g, which
was based on the amount of refrigerant contained in most commercial air conditioning systems (NITE, 2010). In
addition, two leak rates were used: 10 g/min and 60 g/min as the set value.
In this experiment, the concentrations of the refrigerant and hydrogen fluoride (HF) that was produced by combustion
or thermal decomposition were measured using Fourier transform infrared spectroscopy (FT-IR, JASCO, FT-IR4200).

5.3.1.3 Summary
Major findings obtained by the experiments in this scenario are as follows:(1) Even if all of the A2L refrigerant installed inside a room air conditioning system leaked and remained inside
the model general living space (about 7.8 m2), no flame propagation was observed across the entire room
because the refrigerant concentration inside the room did not exceed the lower flammable limit (LFL).
(2) If a refrigerant came into contact with the heated body of the radiative stove or open flame of the fan heater,
HF concentration greater 3 ppm, which is the maximum limit of permissible concentration, was generated
regardless of the variety of refrigerant including R410A, which is the representative refrigerant now in use.
(3) For the case with the radiative stove, the HF concentration increased with the operation of the air conditioning
system and an increase in the leak rate. However, for the case with the fan heater, this trend was not always
confirmed.
(4) HF concentration for the case with the fan heater was greater than that that with a radiative stove.

5.3.2 Scenario #2: Service and maintenance situations
5.3.2.1 Sub-scenario (a): Physical hazard evaluation by smoking inside the space in which an A2L
refrigerant accumulated
OutlineIn this scenario, we evaluated the physical hazard for the case that a commercial portable gas lighter wasused inside a space in which an A2L refrigerant leaked and accumulated at the service and maintenance factory. The
possibility of ignition from the heat of the cigarette tip was ignored because this type of ignition rarely occurs even formethane gas which is well-known for being a highly flammable gas (Holleyhead, 1996).
Mixture composition of the lighter fuel/A2L refrigerant/air
Because details of the method used for determining
the mixture composition of the lighter fuel/A2L refrigerant/air was described in the previous progress report (Imamura
et al, 2013) and reference (Imamura et al, 2013), only an outline is provided in this report.
We assumed n-butane was the fuel of gas lighter, and the mixture of n-butane and A2L refrigerant could be regarded asa single fuel gas. This mixture is called “fuel mixture” in this section. The flammable zone of this fuel mixture in air
was estimated simply using the Le Chaterlier’s relation and assuming that the concentration of n-butane at the outlet ofthe lighter must exceed the LFL. As a result, the concentration of the fuel mixture was within the estimated flammablezone when the A2L refrigerant with concentration less than LFL was mixed with n-butane and air. We focused on the
mixture having this composition.

Experiment
The operation device for a portable gas lighter, which consisted of a pneumatic cylinder (SSD-X,CKD Corp.) and jig was located 300 mm above the bottom of the acrylic pool with dimensions of 1000 mm cube at thecenter of horizontal plane. Air for the operation was supplied remotely using a solenoid valve at a pressure of 0.15

49MPa. A piezo gas lighter and commercial turbo gas lighter were employed as the ignition source.
R1234yf, R1234ze(E), and R32 were employed in the evaluation. The A2L refrigerant was leaked in a downward
direction from a height of 750 mm above the bottom of the pool. The target leakage rate was 10 g/min for all of
refrigerants. The refrigerant concentrations at the 6 vertical positions (0, 100, 300, 500, 750, and 1000 mm in heightfrom the bottom of the acrylic pool) were measured using FT-IR before pushing the button of the piezo gas lighter. The
vertical distribution of the refrigerant concentration was constant for heights less than 500 mm.
The operation to push the button of the lighter was maintained for 2 or 10 s per cycle. This operation was repeated for 5
or 9 cycles at intervals of 5 s per cycle. The situation at the lighter outlet was observed using a digital video camera(SANYO Xacti, 30 fps).

Summary(1) Piezo gas lighter
For the case of the accumulated A2L refrigerant with a LFL concentration, a pale quick emission was observed
near the outlet of the lighter, but the pale emission was quenched 1/30 s later. The flame propagation to theentire refrigerant in surroundings was not observed. For the case of the accumulated A2L refrigerant with aconcentration of LFL/2, an open flame was generated at the gas lighter for several cases. However, the flame
also failed to propagate to the entire refrigerant. These trends were also confirmed for the other refrigerants.
(2) Turbo gas lighter
For R1234yf and R32, the ignition property was nearly identical to the case using a piezo gas lighter. However,for R1234ze(E) with almost an LFL and 71% R.H., a small flame propagation to the refrigerant insurroundings was confirmed for several cases. Afterwards, the experiment was performed using identicalconditions, but flame propagation was not confirmed. Although the apparent reason for this trend has not beenverified, it was considered to be that the concentration of refrigerant at the outlet of a lighter may havedecreased due to the repeated operation of pushing the button, so that the flame generated at the outlet of thelighter propagated to the refrigerant. However, the flame did not propagate to the entire refrigerant insurroundings, it was so quenched 1 - 2 s afterwards.

5.3.2.2 Sub-scenario (b): Physical hazard evaluation when an A2L refrigerant leaks from a pinhole or
fracture in a pipe or hose
OutlineIn this scenario, we assumed the situation that an A2L refrigerant leaked from a fracture or pinhole formedin pipes or hoses during the factory service and maintenance. We evaluated whether some ignition possibilities for theentire refrigerant jet leaked from a fracture or pinhole when there is an ignition source such as an electric spark near the
refrigerant jet. We also evaluated the severity of the refrigerant jet igniting. The results of this scenario are reported in
the references (Imamura et al, 2013, 2014).

100

250

500

50

Regulator
NozzleRefrigerantNozzle100

50Heat flux gage
(Vatell, TG2000-0-2)
Sound pressure sensor(PCB 378B02)

50

Pressure transducer
Pressure gage

50

K-type thermocouple 50（φ0.32 mm）

Ignition source

50

100
100

Concentration meter(a) concentration measurement

Figure 2(b) ignition experiment

Schematic diagram of measuring positions.（Scenario #2, sub-scenario (b)）

50

50

100

250

150

50

50

150

500

Experiment(1) Refrigerant leakage system
The model leakage system consisted of a refrigerant cylinder, balance, regulator, pressure gage, and pinhole
unit. These components were connected by copper and stainless tubes. The outside diameter of these tubes was
6.35 mmϕ (1/4”). The leak pressure was monitored by a pressure gage (Swagelok, PGI63B-MG2.5-LAQX)
and strain gage type pressure transmitter (PGS-20KA, Kyowa Electric Instruments, Co., Ltd.). The pinhole
was modelled using a cap type coupling (1/4”, Swagelok SS-400-C) with a hole in the center. Two patterns
were used for the hole shape: a circular pinhole and rectangular slit. The pinhole diameter was 0.2, 1.0, 3.0,
and 4.0 mmϕ, and the dimension of the rectangular slit was 1.0 mm x 4.0 mm. The 4.0 mmϕ pinhole diameteris assumed to be the very severe accident case, i.e., the pipe or hose is broken. Two patterns were set for the
direction of the rectangular slit: the longer side was oriented either vertically or horizontally.
(2) Concentration measuring system
Before conducting the ignition experiment, concentrations of the leaked refrigerant jet were measured using
five ultrasonic gas analyzers (US-II-T-S, Daiichi Nekken Co., Ltd.). The measured positions of concentration
were at 50, 100, 150, 250, and 500 mm in the downstream direction and -50, 0, 50 mm in vertical direction
from the center of a pinhole, i.e., the concentrations of refrigerant were measured at 15 positions, as shown in
Figure 2(a). The positive value of the height indicates an upward vertical direction from the same center heightof a pinhole. Refrigerant concentrations were measured for 30 s at each position because the refrigerant
concentration approximately attained a uniform value within a period of less than 30 s after opening the valve.
(3) Ignition experiment
In the ignition experiment, a single spark (DC), a continuous spark (AC) and an open flame were employed as
the ignition source. A single spark was generated using a high-voltage system (MEL1140B, Genesis Co., Ltd.):
the energy of the spark was approximately 10 J. A continuous spark was generated using a neon transformer(CR-N16, Kodera Electronics, Co., Ltd.). The open flame length was about 50 mm. These ignition sourceswere located 90 mm downstream from the center of a pinhole with the same height as the center of thepinhole. Temperatures (25 points, by K-type thermocouples with 0.32 mmϕ), heat fluxes (9 pieces ofthermogage, TG2000-2, Vatell Co., Ltd.) and sound pressures (3 pieces of microphone, PCB, 378B02) were
measured. The measured positions of these parameters are shown in Figure 2(b).
(4) Experimental conditions
R1234yf, R1234ze(E), and R32 were used as the test refrigerant. The leak pressure and amount rapidly
decrease with time because the temperature of the leaked refrigerant decreases owing to adiabatic expansion.
Therefore, the repeatability of the mass flow rate and amount was not always well. However, for the actual
accident situation of a pipe breaking, it is considered to be that the leak pressure and amount will decreasesimilar to this experiment. In the actual situation for the service and maintenance, it is considered to be that thepipe of 1/4” ϕ of outside diameter is generally used, so the leakage from hole of 4 mmϕ diameter iscorresponds to very severe accident case. In addition, though the leakage of refrigerant with vapor pressure iscomparatively smaller than the maximum pressure of refrigerant in the air conditioning system in operation,
the operation of the air conditioning system will be suspended in the service and maintenance. Therefore it isconsidered to be that the cases that refrigerant leaked from 4 mmϕ diameter of pinhole with the vapor pressure
are assumed very severe accident cases.
Summary(1) Formation of flammable zone
Figure 3 shows the iso-concentration maps of the refrigerant concentration. The iso-concentration curve isdrawn for every 2.5 vol% except for Figure 3(d), which is drawn for every 1.0 vol%. The iso-concentration
curve of 12.5 vol% for Figures 3(a), (b), (e), and (f) and 5.0 vol% for Figures 3(c) and (d) which correspond toa concentration slightly lower than LFL (R32: 13.5 vol%, R1234yf: 6.8 vol% (Takizawa et al, 2009)) are
shown as bold curves.
Figures 3(a) and (c) show the iso-concentration maps for the 4 mmϕ pinhole without a pressure regulator andassuming that the refrigerant directly leaked from a pipe fracture as the conceivable very severe accident case.
The tip of the bold curve only reached the 100 mm downstream position from a fracture, and the end of the51

bold curve in vertical direction only reached less than ±50 mm. In short, the flammable zone was only formed
locally even for the conceivable very severe accident case.
Figures 3(b) and (d) show the iso-concentration maps for the 0.2 mmϕ pinhole without a pressure regulator andassuming that the refrigerant leaked from a pinhole or crack formed in the pipes or hoses. A flammable zone
was no longer formed. According to Figures 3(e) and (f), influences of the direction of the rectangular slit on
the forming of a flammable zone were hardly confirmed.
(2) Ignition and flame propagation
Figure 4 shows the photos when the leaked refrigerant jet came into contact with the AC continuous discharge,i.e., the ignition source. When the refrigerant leak began, a pale emission near the electrode was observed(Figure 4(a)). Then, the pale emission became larger with time as it traveled downstream away from theignition source, as shown by the open circles in Figures 4(b) and (c). However, because the temperature of theleaked refrigerant decreased with time and the leaked refrigerant was fogged, the pale emission vanished withtime (Figure 4(d), (e)). When the time increased further and the leaked refrigerant jet was steady, a paleemission became visible again. However, the flammable zone was only formed around the electrode, and theflame propagation to entire the refrigerant jet was not observed (Figure 4(f)). In the actual situation for theservice and maintenance, the energy by electrostatic discharge and friction spark discharge can be consideredas the representative ignition source. However, the maximum energy by these ignition sources is less than 1 J.
Even if the A2L refrigerant leaked from the fracture of pipe assuming the very severe accident case, thepossibilities of ignition and flame propagation of A2L refrigerant by the conceivable ignition source in theactual situation is extremely low. Because the ignition and flame propagation were not confirmed in thepresent experiment, an energy of 10 J, which is higher than that in the actual situation was provided to the A2L
refrigerant.

5.3.2.3 Sub-scenario (c): Physical hazard evaluation when an A2L refrigerant leaks inside a device forthe service and maintenance
OutlineIn this scenario, we assumed that the A2L refrigerant leaked in a device for the service and maintenancesuch as the collection device. We experimentally evaluated whether the A2L refrigerant is ignited by spark discharge
from the electric relay inside the device. The results of this scenario are reported in the references (Imamura et al, 2013,2014).
Experiment
The model collection device, i.e., an acrylic pool of 1000 mm cube was produced assuming that theA2L refrigerant leaked in the device for the service and maintenance. The results obtained in the present experimentwill provide more dangerous results than the actual situation because the model collection device will be larger thanthat in the actual situation. The model collection device consisted of five pieces of acrylic board (thickness: 2 mm) anda sheet of vinyl to relieve the pressure rise in the model collection device due to the combustion of the refrigerant. In
the actual situation, a slit is fixed to the collection device to prevent the accumulation of refrigerant in the device if therefrigerant leaks. Therefore, in the present experiment, a pair of slits on the facing planes of the model collection device
was fixed.
The refrigerant concentration in the model collection device was measured using the ultrasonic gas analyzers(US-II-T-S, Daiichi Nekken Co., Ltd.) before ignition. The measuring positions were at the center in the horizontal andat 0, 100, 250, 500, and 750 mm in height. The refrigerant leaked in the upward vertical direction from the 4 mmϕoutlet without the pressure regulator assuming the very severe accident case. The leak rate was approximately 400
g/min, and the leak period was 1 min. The width of the facing slit was varied 0, 1, 5, 10, and 20 mm.
In the ignition experiment, a DC spark (Yokogawa Denshikiki Co., Ltd., 16J) was used as the ignition source. The
ignition source was located at the center of the model collection device. The DC spark was generated 30 s after the
refrigerant leakage stopped. This DC spark was generated six times per second.
Summary(1) Concentration distribution in the model collection device
For w s = 0 mm (w s : slit width), the refrigerant concentration immediately increased after leakage began and52

continued to increase. After the refrigerant leakage ceased 60 s later, the refrigerant concentration slightly
decreased and then it maintained a uniform value. After that the time variation of the refrigerant concentration
was barely observed. It was considered to be that the leaked refrigerant accumulated and remained in themodel collection device.
For w s = 1 mm, after the refrigerant leakage ceased, the refrigerant concentration maintained a uniform value,

Figure 3 Iso-concentration maps near the leaked refrigerant jet. The number in these maps indicates the concentration ofrefrigerant (vol%)Figure 4 Photographs of the leaked refrigerant jet coming into contact with the AC spark discharge.
Refrigerant: R32, Pinhole diameter: 4 mmϕ, Leak rate: 413 g/min

53and then the concentration slowly decreased. The concentration at the comparatively higher position (z = 750mm and 500 mm) decreased with time because the refrigerant diffused to the outside through the facing slit.
However, the decrease in concentration with time near the bottom (z = 0 mm and 100 mm) was slower thanthat at the higher positions (z = 750 mm and 500 mm). The period when the refrigerant concentration at z =500 mm, which is the ignition source was located exceeded the LFL was about 480s.
For w s = 20 mm, after the refrigerant leakage ceased, the concentration of refrigerant immediately decreased
monotonously with time. The trend that the concentration was easy to decrease with time at higher positions
was confirmed. The period when the refrigerant concentration at z = 500 mm exceeded the LFL was about 60s.
(2) Ignition and flame propagation
Figure 5 shows photos of the model collection device with no slit (w s = 0 mm). R1234yf around the ignition
source ignited and a pale flame propagated in upper vertical direction with buoyancy generated by the flame of
the R1234yf. The R1234yf flame approached at the ceiling of the model collection device, and thenpropagated downward. However, flame did not immediately propagate towards the unburned R1234yf because
the burning velocity of R1234yf is very small and oxygen, which is needed to burn, was in short supply. Thus,
the pale flame and unburned R1234yf balanced at a certain height. After that a sheet of vinyl that covered aside plane burned and fresh air flowed into the model collection device. Then, the flame propagated throughthe entire model collection device.
For the actual situation, the conceivable ignition source is the spark discharge at the electrical device inside thecollection device. The maximum energy contained in this spark discharge is a few mJ. The ignition and flame
propagation as shown in Figure 5, are confirmed with 16 J of energy, which is too stronger than the above
spark discharge in the actual situation. In other words, the energy of the spark generated in this experiment ismuch larger than that in the actual situation. Therefore, the ignition and flame propagation, as seen in Figure 5,
for the actual situation is extremely low even if the refrigerant leaked and accumulated inside the collection
device.
On the other hand, for w s = 20 mm, ignition and flame propagation were not observed although theignition spark was generated in the period when the refrigerant concentration exceeded the LFL. This was
because the refrigerant in the model collection device flowed with a particular velocity in the model collection
device. It was considered to be that the burning velocity of R1234yf is very small (1.2 cm/s (Takizawa, et al,2009)): therefore, the flame cannot propagate to the entire R1234yf in the model collection device.

5.3.3 Scenario #3: A2L refrigerant was installed in a VRF system
5.3.3.1 Outline
In Scenario #3, we evaluated the physical hazard when A2L refrigerant installed in a VRF system leaked. In this fiscal
year, we focused on clarifying the properties of the flame behavior, blast wave pressure, temperature, and heat flux(a) t = 0s(b) t = 0.5s(c) t = 1.5s(d) t = 2.5s(e) t = 4.5s(f) t = 5.5s

Figure 5 Photographs of the accumulated refrigerant inside the model collection device.
Slit width: ws = 0 mm, Refrigerant: R1234yf, Leak rate: 380 g/min, Leak amount: 380 g

54

originating from the combustion of the A2L refrigerant as well as clarifying the scale effect of these properties by aseries of laboratory-scale experiments. We focused on two accident cases: (a) the A2L refrigerant leaked into the space
where the ignition source already existed (called “Case (i)”), and (b) the ignition source was generated inside the space
where the A2L refrigerant has already accumulated (called “Case (ii)”),.

5.3.3.2 Experiment
Experimental equipment
An acrylic pool, i.e., 1000 mm cube (with 10 mm thickness board), was developed for the model space. Each face of
this pool was covered by the acrylic boards, but there was an opening of 300 mm x 600 mm in the ceiling. This opening
was covered with a ceramic flange in which a thermogage (TG-2000, Vatell Corp.) and K-type thermocouple (0.32mmϕ) were installed. The face of the flange, thermogage, and tip of thermocouple were located at the same level. A
microphone (378B02, PCB, Inc.) was set at 500 mm near the wall of the pool to measure the pressure of the blast wave
generated by the combustion.
Methods of refrigerant leakage
The refrigerant was leaked in the vertical downward direction through the copper tube with 1/4” outside diameter. The
leak height was varied 0, 500, 750, 1000 mm high above the bottom of the pool. The leak rate was set to approximately
10 and 60 g/min for Case (i) and 10 g/min for Case (ii). The concentrations of the refrigerant at 6 vertical positions (0,100, 300, 500, 750, and 1000 mm in height) were measured by FT-IR before conducting the ignition experiment.
R1234yf and R32 were used as the test refrigerant. The amount of leak refrigerant was set so that the concentration at
the position of ignition source (300 mm in height) achieves LFL, C st , a little higher than C st . The variable of C st
indicates the stoichiometric concentration.
Ignition source
For Case (i), a commercial candle with a flame length of approximately 20 mm was used as the ignition source. In
Case (ii), a commercial match was employed. The tip of the match was put on the Ni-Cr hot wire coil. An AC10V
voltage was supplied to this Ni-Cr hot wire coil through an AC transformer. Then, the match was ignited by the energy
from the Ni-Cr hot wire coil. After a match was ignited, the power supply to the Ni-Cr hot wire coil was immediately
cutoff. In addition, the Ni-Cr hot wire coil without a match was also used as the ignition source to simulate the more
severe scenario.

5.3.3.3 Summary
Distribution of the refrigerant concentration
For the refrigerant leaked near the bottom of the pool, the refrigerant concentration exhibited a comparatively highconcentration at z = 0 m (near the bottom), and the concentration decreased with height. In short, there was the slope ofconcentration in vertical direction. This slope of concentration became easy as the leak height rose. The concentration
slope under 750 mm in height was almost uniform regardless of height in the case of 1000 mm of leak height (leakage
from ceiling).
Combustion behavior(1) Case (i)For the 10 g/min for leak rate, ignition and flame propagation to the entire accumulated refrigerant were
not confirmed, and the candle flame went out automatically. For this case, significant increases in the pressureof the blast wave, heat flux, and temperature were not observed. However, for 60 g/min, a small flame
propagation to the accumulated refrigerant was confirmed.
(2) Case (ii)
For a match flame as the R1234yf ignition source, the accumulated refrigerant ignited for all leak heights. The
humidity was around 50 % R.H. for all cases. The handstand cone shape flame formed, and this flame moved
and propagated in an upward vertical direction owing to the buoyancy originating from the flame itself. The
flame was maintained for some time after coming into contact with the pool ceiling. A significant increase in
the pressure of the blast wave was observed. The maximum temperature increase was about 900 °C. The flame55

propagation to the accumulated refrigerant under the ignition source was not observed.
For a Ni-Cr hot wire coil as the R1234yf ignition source, ignition and flame propagation were not confirmed
for all cases. For these cases, the humidity was about 20 - 30 %R.H. This indicates: such that the ignition andflame propagation greatly depended on the humidity not the ignition source.
For R32, it was ignited using both a match flame and Ni-Cr hot wire coil. The humidity of these cases was 30 60 % R.H., and the influence of humidity on the combustion behavior of R32 was hardly confirmed. A flatted
fireball shape flame formed near the ignition source. Afterwards, the flatted fireball flame rose with thebuoyancy, which originated from flame itself, and collided with the ceiling. The flame remained at the ceilingfor some time, after that it automatically quenched. The significant increases in the blast wave, temperature,and heat flux were observed. These parameters were greatly affected by the leak height. The pressure of blast
wave obtained for 500 and 750 mm height exhibited comparatively higher values. Because there were large
amounts of refrigerant that exceeded the LFL located at the space above the ignition source.
However, at most, pressure of the blast wave only corresponds to the phenomena that the 10 mm thick acrylic
board was slightly lifted. The pressure of the blast wave that breaks the acrylic pool (1m3 cube) was not
generated.

5.4 Conclusions
5.4.1 Scenario #1: Simultaneously used with a fossil-fuel heating system
In this scenario, no flame propagation to the entire refrigerant was observed and HF generation as much as R410A, i.e.,
the present representative refrigerant was confirmed. More HF was generated when there were some flows inside theroom.

5.4.2 Scenario #2: Service and maintenance situation(1) We conducted the physical hazard evaluation assuming that a serviceman used a portable gas lighter to smoke
where the A2L refrigerant accumulated. It was verified that there are several possibilities that the mixture
composition of a lighter fuel/A2L refrigerant/air exceeds the LFL. However, although the ignition experimentusing a commercial piezo gas lighter was conducted above the estimated mixture composition, no ignition andflame propagation were observed in any of the tested refrigerants (R1234yf, R1234ze(E), R32). For acommercial turbo gas lighter, ignition and flame propagation near the outlet of the lighter was observed forsome R1234ze(E) cases. The relative humidity in this case was 71 % R.H. and room temperature was 19 °C.
However, the flame quickly went out, and a blast wave pressure capable of breaking an acrylic pool was notconfirmed.
(2) We conducted the physical hazard evaluation assuming that the A2L refrigerant leaked from a fracture or
pinhole in the pipes or hoses. Even if the refrigerant leaked from a 4 mmϕ pinhole, which is the conceivablevery severe accident case, a flammable zone was only formed locally around the pinhole for all test
refrigerants. Even if the energy is much larger than that of an electrostatic and spark discharge which arepossible in actual situations, the flame propagation to the entire refrigerant jet was not observed, andsignificant increases in blast wave pressure, heat flux, temperature, and HF concentration were not confirmed.
Therefore, even if the A2L refrigerant leaked from the pipe fracture, the possibility of ignition and flame
propagation of the A2L refrigerant by the conceivable ignition source in the actual situation is extremely low.
(3) We conducted the physical hazard evaluation assuming that the A2L refrigerant leaked into the device for theservice and maintenance. If there was no structure to diffuse the leaked and accumulated refrigerant, theleaked refrigerant in the device accumulated and remained long time. It could be ignited, and the flame could
propagate the entire device by a strong spark of 16 J. However, the possibilities of ignition and flame
propagation of the accumulated refrigerant are extremely low because the generation of that much energy ishardly in actual situations. In addition, the minimum ignition energy of the A2L refrigerant is much larger than
the spark discharge energy generated from the electrical device in the collection device. If there was a slit witha width greater than 20 mm, the accumulation of the refrigerant inside the device could be immediately

56

prevented, and most of the ignition and flame propagation could be prevented.

5.4.3 Scenario #3: A2L refrigerant was installed in a VRF system
We conducted the physical hazard evaluation assuming that the A2L refrigerant leaked from a VRF system in thelaboratory-scale experiment. The distribution of refrigerant concentration in a pool greatly depended on the leak height.
The trend that large slope of concentration in vertical direction was confirmed so that the leak height was lower. In theignition experiment, the flame propagated upward in the vertical direction, and significant increases of the blast wave
pressure, temperature, heat flux, and HF concentration were confirmed. It was found that the scale of the flame
propagation and increases of these parameters depend on the amount of refrigerant that exceeded LFL located above an
ignition source. However, the pressure of blast wave slightly lifted the 1000 mm x 1000 mm x 10 mmt (12 kg weight)
acrylic board. The pressure of the blast wave that breaks the acrylic pool (1m3 cube) was not generated.

Acknowledgements
This study has been conducted as a part of the “Technology Development of High-Efficiency Non-fluorinated Air
Conditioning Systems” research project and performed by the New Energy and Industrial Technology Development
Organization (NEDO). The authors would like to sincerely thank Dr. Tatsuya Miyashita a former graduate student ofTokyo University of Science, Mr. Hiroyuki Mitsuishi, Dr. Yohsuke Tamura and Mr. Masayuki Takeuchi of Japan
Automobile Research Institute (JARI), Mr. Takanori Morimoto, Dr. Kyoko Kamiya and Mr. Yuta Yamazaki of Japan
Specialist in Law Engineering Corporation, and Mr. Shunta Nakamura and Mr. Shunsuke Mashimo undergraduate
students at the Tokyo University of Science, Suwa for their kind supports with the experiments.

References
Holleyhead, R.: “Ignition of Flammable Gases and Liquids by Cigarettes: a Review”, Science and Justice, 36(4),(1996), pp.257-266.
Imamura, T. and Sugawa, O.: Physical hazard evaluation of A2L-Class Refrigerants using Several Types ofConceivable Accident Scenarios, Risk assessment of mildly flammable refrigerants 2012 Progress Report (2013),
pp.35-42.
Imamura, T., Miyashita, T., Kamiya, K., Morimoto, T. and Sugawa, O.: Physical hazard evaluation for using air
conditioning systems having low-flammable refrigerants with the fossil-fuel heating system at the same time,
Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers, Vol.29, No.4 (2012),
pp.401-411 (in Japanese).
Incorporated Administrative Agency National Institute of Technology and Evaluation (NITE):
http://www.prtr.nite.go.jp/prtr/pdf/estimation23/syosai/syosai23t.pdf, (2010), (in Japanese).
Imamura, T., Miyashita, T., Kamiya, K. and Sugawa, O.: Ignition hazard evaluation on leaked A2L refrigerants bycommercial-use electronic piezo lighter, Journal of Japan Society for Safety Engineering, Vol.52, No.2 (2013),
pp.91-98 (in Japanese).
Imamura, T., Morimoto, T., Yamazaki, Y., Kamiya, K., Mitsuishi, H. and Sugawa, O.: Experimental study on ignition
hazards of leaked A2L refrigerant from a pinhole, Proceedings of Asia Pacific Symposium on Safety 2013,
Singapore (2013), Paper No.C3-03.
Imamura, T., Kamiya, K. and Sugawa, O.: Ignition hazard evaluation on A2L refrigerants in situations of service andmaintenance, 10th International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions,
Bergen (2014), submitted.
Takizawa, K., Tokuhashi, K. and Kondo, S.: Flammability assessment of CH 2 =CFCF 3 : Comparison with fluoroalkenes
and fluoroalkanes, Journal of Hazardous Materials, Vol.172 (2009), pp.1329-1338.

57

6. Progress Report of Research Institute for Innovation in Sustainable
Chemistry, AIST
6.1

Introduction

This research involved evaluating the flammability of low-GWP refrigerants under practical conditions and thedevelopment of an ignition energy evaluation method for them. The flammability properties of these refrigerants were
evaluated under various temperature and humidity conditions considering their practical applications, and their safety interms of flammability was compared with that of nonflammable refrigerants currently in use. The ignition energy
evaluation method was developed to improve the current situation, where there is a wide variation in published ignitionenergy values for mildly flammable compounds, in order to provide a reliable index on fire risk. In this report, we
describe our progress on these three subjects.

6.2

Evaluation of flammability under practical conditions

6.2.1

Temperature and humidity dependence of flammability properties(a) Temperature and humidity effects on flammability limits of several 2L refrigerants: The effects of temperatureand humidity on the flammability limits of refrigerants are important because the refrigerants are used under various
conditions. Typical 2L compounds were measured following the ASHRAE method. Table 6.1 lists the observed
temperature coefficients of the flammability limits. In general, the temperature dependence of the flammability limits
can be explained by White’s rule. According to this rule, the lower and upper flammability limits are expressed by thefollowing equations:

 100C p , L

 100C p , L(t −25)
L = L25 1−
 L25 ⋅ Q
and U = U 25 1+

L25 ⋅ Q(t −25)
(6.1)

where L 25 and U 25 are the lower and upper flammability limits (vol%) at 25 °C, respectively; C p,L is the heat capacity of
unburned gas at the lower flammability limit; and Q is the molar heat of combustion of the fuel gas.
Table 6.1: Temperature dependence of flammability limits of several 2L refrigerants
Refrigerant

LFL

UFL

Obs.

Pred.

Obs.

Pred.

R717

-0.0086-0.0095

0.02080.0189R32-0.0070-0.00640.00910.0133R143a-0.0051-0.0038

0.00800.0093

R1234yf (dry)-0.0133-0.00290.01020.0052

R1234yf (wet)-0.0045-0.00280.00980.0071

R1234ze(E) (wet)-0.0104-0.00290.01740.0061

As presented in the above table, the temperature dependences of the flammability limits for ammonia, R32, andR143a basically agree with the values predicted by the above equations. However, the temperature dependences of the58flammability limits of R1234yf and R1234ze(E) were considerably larger than those predicted by the equations.
With regard to the humidity effect on the flammability limits, measurements were performed over a humidity range of
0%–90% corrected for a temperature of 23 °C. The flammability limits of ammonia, R32, and R143a were found to not
be greatly affected by the humidity of air. On the other hand, the flammable ranges of R1234yf and R1234ze(E), whosemolecules contain more F-atoms than H-atoms, were found to be markedly dependent on the humidity. Figure 6.1
shows the humidity effect on the flammability limits of R1234yf and R1234ze(E).

Figure 6.1: Humidity effect on flammability limits of R1234yf and R1234ze(E)All the measurements were performed at 35 °C.
(b) Flammability property of non-flammable refrigerants under high humidity conditions: The effect of relatively
high humidity (i.e., up to 50% at 60 °C) on the flammability property in air was measured for R410A, R410B, R134a,and R125. The measurements were performed following the ASHRAE method. Under this humidity condition, R410A,
R410B, and R134a became flammable, whereas R125 did not. For the first three samples, the limiting humidity
condition to make the gas flammable was determined. In addition, the effect of temperature up to 100 °C was examined
for these materials at a relative humidity of 50% corrected for a temperature of 23 °C. The results showed that all four
samples remained non-flammable under this condition. Table 6.2 lists the observed flammability limits of R410A,
R410B, and R134a at a relative humidity of 50% and temperature of 60 °C.
Table 6.2: Flammability properties of R134a, R410A, and R410B at a relative humidity of 50% andtemperature of 60 °C
Refrigerant

LFL

UFL

vol%

±

vol%

±

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

(c) Flammability limits for binary mixtures of ammonia with multi-fluorinated compounds: Flammability limits
for binary mixtures of ammonia with R1234yf, R1234ze(E), R134a, and R125 were measured in dry air. The
measurements were made using the ASHRAE method. The flammability limits of ammonia and R1234yf mixtures were
found to be very different from the values predicted by Le Chatelier’s equation. Le Chatelier’s equation was modified
by introducing an ellipse function to analytically express the flammability limits of the mixtures of arbitrary
concentrations as follows:22
1 L = (cam Lam )1 + p1c yf + p2 c yf − c yf  + (c yf Lyf )1 + p3cam + p4 cam − cam  (6.2)
where L, L am , and L yf are the flammability limits of the mixture, ammonia, and R1234yf, respectively. c am and59

c yf are the fractions of ammonia and R1234yf, respectively, in the mixture, and c am + c yf = 1. p 1 –p 4 areparameters that are adjusted to appropriately explain the observed values. Figure 6.2 compares the observed andcalculated values for ammonia/1234yf mixtures; the open circles represent the observed values, the solid lines
show the calculated values, and the dotted lines show the values predicted by Le Chatelier’s equation.

Figure 6.2: Flammability limits for R717/R1234yf mixtures
All the measurements were performed at 35 °C.
R1234ze(E) was found to be non-flammable in dry air but flammable if more than 4% ammonia was added. If theammonia content exceeded 20%, the flammability limits became very close to the corresponding ones for R1234yf andammonia. In contrast, the flammable regions of ammonia mixed with those of R134a and R125 were much narrower
than the mixtures of R1234ze(E). The ellipse-modified Le Chatelier’s equation was extended to successfully explain the
flammability limits of these mixtures as follows:22
1 L = (x am Lam )1 + q1 x ze + q 2 x ze − x ze  + (x ze LFIP )1 + q3 x am + q 4 x am − x am  (6.3)
where L and L am are the flammability limits of the mixture and ammonia, respectively, and L FIP is the limiting
mixture concentration at FIP. x ze = c ze f and x am = 1 - x ze , where f is the extension factor and c ze is the fraction of
R1234ze(E) in the mixture. q 1 –q 4 are parameters that are fitted to the observed values. Note that Equation (6.3)
coincides with Equation (6.2) when f is equal to unity. Figure 6.3 compares the observed and calculated
flammability limits of the ammonia/1234ze(E) mixtures. In this case, FIP was located at c ze 0.96; therefore, theextension factor became 1.04. The flammability limits of ammonia/134a and ammonia/125 mixtures can also be
explained by using the above equation.

Figure 6.3: Flammability limits for R717/1234ze(E) mixtures
All the measurements were performed at 35 °C.

60

(d) Humidity effects on burning velocity of several 2L refrigerants: The combustion reaction of R1234yf with thesurrounding air is expressed by the following equation:
CH 2 =CFCF 3 + 2.5O 2 + yH 2 O = (2 + 2y)HF + (1 − y)COF 2 + (2 + y)CO 2 + (1169 + 57y) kJ (6.4)
where y denotes the moles of water vapor in the gas mixture.
Since the fluorine-to-hydrogen ratio of R1234yf molecules is higher than unity, excess fluorine produces COF 2 without
proceeding to HF formation when in dry air. With the addition of a hydrogen-supplying compound such as water vapor
into the reaction system, fluorine can produce HF, which increases the heat of combustion. When the F/H ratio becomes
unity, the heat of combustion becomes maximum. Similar behavior was expected for R1234ze(E) in moist air, but theheat of combustion was slightly lower than in the case with R1234yf.
Figure 6.4 shows the dependence of S u on the refrigerant concentration at the absolute humidity of 0.03 g-water/g-dry
air. For both R1234yf and R1234ze(E), S u showed similar tendencies as the refrigerant concentration and reached its
maximum at slightly refrigerant-lean conditions. S u,max was ca. 6 cm s-1 for 1234yf and 5 cm s-1 for 1234ze(E). S u may
continue to increase with the absolute humidity until 0.052 g-water/g-dry air, as suggested by the increased heat of
combustion in Equation (6.4). For comparison, a similar flammability test was done for R32 in moist air. The heat of
combustion was unchanged by humidity because R32 has an F/H ratio of unity. The stoichiometric S u in moist air at an
absolute humidity of 0.022 g-water/g-dry air was 6.7 cm s-1, which is almost the same as S u,st of 6.6 cm s-1 in dry air.
Thus, humidity does not affect the flammability of R32.

101234yf

Su , cm s-1

8
6
4

1234ze(E)21234yf(dry)
0
6

7

8

9

10

11

12

Refrigerant concentration, vol%Figure 6.4: Concentration dependence of S u at 25 °C for R1234yf and R1234ze(E) in moist air at absolute humidity of
0.03
The flammability of R1234yf may increase with the humidity until the overall F/(H + F) in the gas mixture reaches 0.5.
However, it was difficult to obtain the worst case at the ambient temperature because of the difficulty with controllingthe high humidity. Instead of water vapor, we used ammonia as the hydrogen-supplying compound. Figure 6.5 shows
the S u,st vs. mixing ratio of the hydrogen-supplying compound for the R1234yf−NH 3 system. Similar to theR1234yf−H 2 O system, S u,st of R1234yf+NH 3 increased with the added NH 3 and became maximum at R1234yf:NH 3 =1:1. The corresponding S u,st was 8.6 cm s-1, which is even higher than the S u, max of pure NH 3 .

61

,

10

Su,st , cm s-1

8
6
4
1234yf+NH3
R-1234yf+NH3
2

R-1234yf+H2O
1234yf+H2O

0

0.2
0.6
0.5
0.4
0.3
0.1
0
pure NH3
pure R-1234yf
Overall F/(H+F) ratio in the mixture

Figure 6.5: S u,st vs. mixing ratio of hydrogen-supplying compound: R1234yf−H 2 O and R1234yf−NH 3 .
(e) Humidity effect on quenching distance of R1234yf: Details on the quenching distance measurement are describedin section 6.3. In this section, we discuss the humidity effect on the quenching distance of R1234yf. Experiments wereconducted at 25 °C in dry air and 60 °C in moist air. First, we determined the concentration that provides the optimum
d q,h to be 8.8 vol% at 50% RH. Second, we fixed the R1234yf concentration at 9 vol% and measured d q,h over a wide
range of humidity. Figure 6.6 shows the humidity effect on d q,h for R1234yf. When moisture was added to the gas
mixture, d q,h decreased dramatically. d q,h became less than 5 mm at ca. 40% RH, which corresponded to an overall F/H
ratio of ca 1.0.

Figure 6.6: Humidity effect on quenching distance of R1234yf. Dry conditions: 25 °C and 10 vol% in microgravity.
Wet conditions: 60 °C and 9 vol% in Earth gravity.
As discussed above, the flammability limits, burning velocity, and quenching distance of R1234s became worse as thehumidity of air increased. This is because these compounds have a much higher F/H ratio than unity and H 2 O
molecules supply H atoms to the reaction system. If these compounds are used at the optimum humidity, theirflammability will exceed that of ammonia. Thus, care should be taken when R1234yf and R1234ze(E) are mixed with acompound having an F/H ratio of less than 1.0, such as ammonia. Such a mixture will show higher flammability than
expected from the individual components.

6.2.2 Flammability evaluation in comparison with nonflammable refrigerants in use(a) Toward establishment of index on degree of non-flammability: Many refrigerants are mixtures of a few
different compounds. They usually contain non-flammable components. At present, however, there is no way of
estimating the degree of non-flammability. Thus, we recently introduced the concept of limiting methane62

concentration (LMC): the minimum methane concentration to be added to non-flammable gas to make themixture flammable. On the other hand, to establish an index to measure the degree of non-flammability, an
indicator is needed that varies linearly with the mixing ratio of the added non-flammable component to aselected standard flammable gas. The F-number is known to greatly deviate from linearity with decreasing
flammability when mixed with a non-flammable component. Instead, we introduce the new F2-number, which isdefined by the following equation:

F 2 = (U − L ) UL (6.5)
2This value is the square of the normalized flammable range and approximates the strength of the combustion
power.
The next question is how to select a standard flammable gas. For the above LMC, methane was selected as thestandard gas. However, as was apparent for ammonia, which was considered in the preceding section, methane
is not necessarily a good standard gas. This is because methane as ammonia has excess hydrogen atoms in themolecule, so interactions occur between combustion reactions if they are mixed with molecules having excess
fluorine atoms. Therefore, we adopted R32 as a standard gas as it has equal numbers of hydrogen and fluorine
atoms in the molecule. Figure 6.7 plots the F2-number against the mixing ratio of various gases to R32. The top
one is for nitrogen and carbon dioxide; the middle one is for methane, R152a, and R1234yf; and the bottom one
is for R1234ze(E), R134a, and R125. The linearity was good for nitrogen and carbon dioxide; fair for methane,
R152a, R125, and R134a; and poor for R1234yf and R1234ze(E).

Figure 6.7: F2-number versus mixing ratio of various gases to R32(b) Thermal decomposition of refrigerants: The effects of the R1234yf concentration and total flow rate on thethermal decomposition of R1234yf were investigated by using a flow reactor. The thermal decomposition of
R1234ze(E) and R22 was studied at φ = 1 and a total flow rate of 100 cm3/min. Figure 6.8 shows a schematic diagramof the experimental apparatus. The flow rates of the refrigerant and air were measured and controlled by calibrated mass
flow controllers, and the refrigerant/air mixture was continuously supplied to a heated tube reactor (Inconel, 12.7 mm
outer diameter, 10.2 mm inner diameter, 44 cm length). The reaction temperature was measured by thermocouples (1mm outer diameter, Type K) that were inserted in the tube (Inconel, 3.175 mm outer diameter, 1.4 mm inner diameter,
62 cm length) at the center of the reactor tube. The concentrations of the refrigerant and decomposition products such as
HF were measured by using FT-IR (cell length was 10 cm, ZnSe windows). The O 2 concentration was measured by GC(TCD detector, Ar carrier, 3 mm diameter × 3 m length SUS column packed with Molecular Sieve 13X-S, column
temperature of 30 °C). To adjust the IR intensity, N 2 was added to the reaction gas immediately behind the reactor. The
gas was treated with soda lime before being introduced to GC. The exhaust gas was also treated with soda lime. The
experiment was started at room temperature, and the temperature was increased in a stepwise fashion. The refrigerant,
O 2 , and products were measured under steady-state conditions.

63

Reactor (Inconel)

Heater

TC

TC

N2

GC

Refrigerant
IR cellAir

Figure 6.8: Schematic diagram of experimental apparatus
The dependency of the thermal decomposition on the R1234yf concentration was studied at concentrations of 1.0 vol%(φ = 0.12) to 15.0 vol% (φ = 2.10) at a constant total flow rate (100 cm3/min). Figures 6.9 and 6.10 show the thermal
decomposition results of R1234yf for R1234yf = 1.0 and 15.0 vol%, respectively. Here, O 2 consumption and products
such as HF were based on the supplied mole of R1234yf. R1234yf was observed to decompose at a certain temperaturedepending on the concentration and total flow rate, and the decomposition considerably increased at this temperature.
For R1234yf = 7.8 vol% (φ = 1.0), decomposition of R1234yf was observed at around 600 °C or higher, and thedecomposition temperature increased with decreasing R1234yf concentration (decomposition temperature for R1234yf= 5.0, 3.0, 2.0, and 1.0 vol% were around 620–630, 630–640, 660–720, and 670–770 °C, respectively). On the other
hand, the decomposition temperature did not change if φ > 1, as shown in Figure 6.10. The major products were HF,
COF 2 , CO 2 , and CO; O 2 consumption and products such as HF increased with the decomposition rate of R1234yf. No
detectable differences were observed between the clean reactor and reactors that had been used in previous experiments.
The dependency of the thermal decomposition on the total flow rate was studied between 20 and 200 cm3/min at aconstant R1234yf concentration of 7.8 vol%. When the total flow rate was increased, the decomposition temperature
was also found to increase (decomposition temperatures for total flow rates of 20, 50, 100, and 200 cm3/min werearound 570–580, 600 or slightly lower, 600, and 630 °C, respectively).

Figure 6.9: Results for thermal decomposition of R1234yf: R1234yf = 1.0 vol% (φ = 0.12), total flow rate = 100
cm3/min64

Figure 6.10: Results for thermal decomposition of R1234yf: R1234yf = 15.0 vol% (φ = 2.10), total flow rate = 100
cm3/minFigure 6.11 shows the thermal decomposition results of R1234ze(E). R1234ze(E) was observed to decompose at 550 °C
or higher, and consumption of O 2 and products such as HF were observed at 600 °C or higher when the clean reactor
was used in the experiment. When a contaminated reactor was used in the experiment, however, R1234ze(E) was
observed to decompose at 350 °C or higher, whereas consumption of O 2 and products such as HF were not observed up
to around 550 °C. The reproducibility of the consumption rate for R1234ze(E) at 350–550 °C was good; however, theopen small symbols in Figure 6.11 represent the results of three experiment runs, and the amounts of decomposition
products in the reactor may have differed. Note that, at 550–600 °C, R1234ze(E) consumption was observed; in contrast,
O 2 consumption and products were not observed in this temperature range if a clean reactor was used. Therefore, in thistemperature range, the consumption of R1234ze(E) may be affected by trace amounts of decomposition products. Whenthe reactor tube was contaminated by more than the threshold value of decomposition products, the temperature fordecomposition initiation of R1234ze(E) decreased by approximately 200 °C; the decomposition of R1234ze(E) did notdepend on the amount of decomposition products that was attached to the reactor tube.

200

200

60

150

40

100

20

50

0

0

200

400

600

0
800

HF
COF2
CO2
CO
CF4

150

2.0
1.5

100

1.0

50

0.5

0

temperature, °C

2.5
CF4 production, %R1234ze(E)250production, %R1234ze(E)
O2

80

250

O2 consumption, %

100

0

200

400

600

0
800

temperature, °C

Figure 6.11: Results for thermal decomposition of R1234ze(E): R1234ze(E) = 7.8 vol% (φ = 1), total flow rate = 100
cm3/min. Open small symbols represent measurements taken when decomposition products contaminated the reactor
Figure 6.12 shows the thermal decomposition results of R22. The consumption of R22 and O 2 and products such as HF
were observed at 450 °C or higher when a clean reactor was used for the experiment. At 450–650 °C, the consumption

65and production gradually increased with increasing temperature. When a contaminated reactor was used for theexperiments, R22 consumption was observed at 300 °C or higher, whereas O 2 consumption and products such as HF
were not observed up to around 450 °C. At 450 °C or higher, no differences between clean and contaminated reactors
were observed for O 2 consumption and production such as HF. When a contaminated reactor was used, a large scatter
was observed for R22 consumption at 300–600 °C. Thus, R22 consumption may depend on the amount of
decomposition products.

150

80
60
40

1.5

HF
COF2
CO2
CO
HCl
CF4

100

CF4 production, %R22
O2

production, %consumption, %

100

1.0

0.5

50

20
0

0

200

400

600

temperature, °C

0

800

0

200

400

600

0
800

temperature, °C

Figure 6.12: Results for thermal decomposition of R22: R22 = 21.9 vol% (φ = 1.0), total flow rate = 100 cm3/min.
Open small symbols represent measurements taken when decomposition products contaminated the reactor

6.3 Development of ignition energy estimation method
6.3.1 Estimation of minimum ignition energy
For 2L compounds with a maximum burning velocity (S u,max ) of less than 10 cm s-1, the reported E min varies widelyfrom below 10 mJ to over 10 J. This makes assessing the fire risk based on E min very difficult. The difficulty indetermining a reliable E min lies in the fact that E min is very dependent on the electrode size, the gap between theelectrodes, and the ignition spark density and duration. Compared to E min measurement, d q measurement seems to bemuch easier and provide more reliable data for mildly flammable compounds. Therefore, we first carry out
comprehensive measurement of d q for compounds having a wide variety of flammability intensities and then attempt toestimate E min by using the experimental burning velocity (S u ) and d q . To obtain a test method appropriate fordetermining d q of various compounds under equivalent test conditions, we tested various conditions such as thegeometry and size of the electrodes.
(a) Quenching distance measurement: The experimental setup and procedure were similar to ASTM-E582. The target
compounds were the highly to only mildly flammable 11 compounds listed in Table 6.3. For the combustion vessel, thecylinder (inner diameter; 160 mm, length; 150 mm) was made of acrylic plastic. The cathode electrode was fixed,
whereas the anode electrode could be moved with a micrometer to provide an adjustable gap within 0.001 mm. The
parallel plates were made of machinable glass ceramic (Macor) instead of the borosilicate glass specified in
ASTM-E582. The plates could be removed from the electrodes; we tested plates with diameters of 5, 25, 50, 75, and100 mm to examine the effect of the plate size on d q . We judged whether ignition could be achieved between theparallel plane plates. We obtained d q by changing the gap between the plates with a micrometer. d q was determined as
the average value between the maximum gap width at which flame propagation could not be observed in ten successive66

experiments and the minimum gap width at which flame propagation could be observed within ten successive
experiments.
Because the slowly propagating flame was significantly affected by the buoyancy, we measured d q both in the vertical
position (i.e., same position as the ASTM-E582 apparatus) d q,v and in the horizontal position d q,h of the parallel plates.
For R1234yf, a reliable d q,h has not yet been obtained. d q,v increased almost monotonically with increasing plate size,
and we may not have determined the converged values. We performed a microgravity experiment at the AIST Hokkaido
center to remove the buoyancy effects and obtain more reliable d q for R1234yf.

Name

PropaneIsobutane
R152a1243zf
HFC-143
R152a/134a(50/50vol%)HFC-254fb
R143a
Ammonia
R32
R1234yf

Table 6.3: Measured quenching distance and estimated E min for 11 compounds
FormulaS u,max ,d q,h ,
d q,v,
φ min
Estimated E min b),
Calibrated E min b,
-1
c)
cm s
mm
mm
mJ
,
mJ
C3 H8
38.7
1.70
1.70
1.13
0.35 (0.35)
0.247(CH 3 ) 2 CHCH 3
34.2
2.00
1.16
0.62
0.44
CH 3 CHF 2
23.6
2.33
1.17
0.90
0.63
CH 2 =CHCF 3
14.1
3.33
1.24
2.2
1.5
CH 2 FCHF 2
13.1
3.58
3.48
1.30
2.9 (2.6)
2.0 (1.8)
CH 3 CHF 2
11.7
4.08
3.88
1.29
3.8 (3.0)
2.7 (2.1)/CH 2 FCF 3
CH 2 FCH 2 CF 3
9.5
5.23
4.35
1.35
12 (5.3)
8.4 (3.7)
CH 3 CF 3
7.2
7.03
6.00
1.36
27 (13)19 (9.4)
NH 3
7.1
8.95
7.45
0.99
45 (19)32 (14)
CH 2 F 2
6.7
7.55
6.45
1.19
29 (14)20 (9.8)
CH 2 =CFCF 3
1.5
24.75a)16.75
1.23
770 a) (80)
540 a) (56)a) d q measured in microgravity. b) number in parentheses is E min estimated from d q,v. Others estimated from d q,h. c) 11% reduction of adiabatic flamezone diameter d q - δ to make the E min of propane equal to 0.247 mJ, which is the most cited value reported by Lewis and Von Elbe (1987).

First, we examined the effect of the size of the parallel plane plates on d q . Figure 6.13 shows the results for sevencompounds at the concentrations of the lowest d q,h . For propane, the converged d q,h value was obtained by using plateswith diameters of 25 mm or larger. For R32 and ammonia, however, the 25-mm diameter plates were not sufficiently
large to obtain the converged d q,h values. The d q,h of R32 and ammonia were 5.95 and 6.85 mm, respectively, with
25-mm plates and 6.45 and 7.45 mm, respectively, with 100-mm plates in the vertical position. ASTM–E582 specifies
that the plate diameter be 5–10 times the electrode gap, as indicated by the chain line in Figure 6.13; this appears to bereasonable based on the observations in the present study.
Table 6.3 lists the converged d q,v and d q,h for all of the compounds except R1234yf. For R1234yf, the d q,v and d q in
microgravity with 100-mm plates are listed, although the 100-mm diameter plates did not seem to be sufficiently large
to obtain the converged d q for R1234yf.
10

D = 5 ×dq

Quenching distance (dq,h), mm

98

Ammonia
R-32

7

R-143a6

HFC-254fb
5

R-152a/134a (50/50vol%)4
3

HFC-1432

Propane

1
0
0

20

40

60

80

Diameter of parallel plates (D), mm

67

100

Figure 6.13: d q,h versus diameter of parallel plates(b) Estimation of minimum ignition energy: The minimum ignition energy is the energy that is just necessary toestablish the minimal flame sphere with the minimum radius necessary for self-sustained propagation. According to thesimple heat loss theory proposed by Lewis and Von Elbe (1987), E min is written by

Emin = (1 / 6 )p d min ρb c p (Tb − Tu ) (6.6)
3Here, d min is the diameter of the minimal flame in free space; ρ b is the burned gas density; c p is the average isobaric
heat capacity; and T b and T u are the burned and unburned gas temperatures, respectively.
Solving Equation (6.6) requires T b and the size of the minimal flame to be determined. Lewis and von Elbe (1987)
postulated that the minimal flame has a diameter that is equal to the parallel plate quenching distance d q and the same
temperature as the adiabatic flame temperature T ad . Their calculated E min qualitatively agreed with the experimental
values for various compounds but was quantitatively several times greater than the experimental E min on average.
We examined the relationship between d min in Equation (6.6) and the parallel plate quenching distance d q by measuring
the minimum flame radius of the self-sustained propagating flame r f,min for the R32/air mixture at 21 vol% (φ = 1.27).
Note that since the Schlieren technique visualizes the change in density, the r f obtained from the Schlieren image
includes the flame kernel radius and most of the flame thickness.
By comparing the measured quenching distance and minimum flame diameter for R32, the parallel plate quenching
distance d q,h was found to be substantially equal to the minimum flame diameter 2r f,min . Thus, the two different test
results were confirmed to substantially represent the same quenching processes.
Based on the previous discussion, Equation (6.6) is rewritten as.
Emin = (1 / 6 )p (d q − 2d ) ρb c p (Tb − Tu )
δ = 2λav (c p ρu Su , max ) (6.8)
3

(6.7)

Here, we considered d min in Equation (6.6) to be the diameter of the flame kernel. Assuming that T b = T ad , E min was
obtained from the experimental d q and S u,max . The results are listed in the seventh column of Table 6.3. Overall, E min as
estimated by Equation (6.7) was slightly higher than the lowest experimental E min values reported in the literature.
However, the agreement between the calculated and experimental E min was considered to be better than that in theliteratures. For propane, the estimated E min of 0.35 mJ was approximately 40% higher than the lowest experimental
value of 0.247 mJ reported by Lewis and Von Elbe (1987) but well within the range of reported E min values. We
calibrated the calculated E min by decreasing the flame kernel diameter (d q – 2d) in Equation (6.7) by 11% so that theE min of propane would become the most cited value of 0.247 mJ; these values are listed in the eighth column of Table
6.3. Such calibration is justified considering the similarity in the minimal flame structures for all of the compounds.
For 2L refrigerants, the estimated E min was considerably lower than the values in the literature that were measured by
the ASTM E582 method.

6.3.2 Flame extinction diameter
When an electrical component with openings, such as a circuit breaker or magnetic contactor, operates in a flammablegas atmosphere, the electric spark generated by the component can be an ignition source. Even though ignition occurs at
the electrode gaps inside the enclosure, combustion will not be transmitted to the flammable gas atmosphere outside theenclosure unless the diameter of the opening of the enclosure exceeds the critical value d*. In this report, we call d* the“extinction diameter.” Figure 6.14 shows a schematic drawing of the apparatus for measuring the extinction diameter.
Experiments were carried out in the same vessel used for the quenching distance measurement. A thin square PTFE
plate with a circular opening was set at a distance h from the ignition point. The plate had a thickness of 1 mm. We
observed whether the flame sphere could go through the opening.

68

b

a
e
i

c
d

h

h

f
＋

－

a: acrylic cylinder
b: stainless steel flange
c: sample gas inlet
d: gas outlet to vacuum pump
e: mixing fan
f: thermocouple (type K)
g: spark generator
h: electrodes
i: PTFE plate with an openingg

Figure 6.14: Apparatus for extinction diameter measurement
Figure 6.15 shows the measured d* as a function of h for three 2L compounds: R32, R717, and HFC-254fb. In the small
h region, d* decreased rapidly with increasing h. As h increased further, d* decreased gradually and finally reached analmost constant value. This tendency may reflect the formation process of stable flames.
8

R-32

7

R-717

d* , mm6

HFC-254fb

5
4
3
2
1
0
0

10

20

30

40

50

60

70

h , mmFigure 6.15: d* vs. h for R32, R717, and HFC-254fb
Considering the application of d* to practical risk assessment, the effect of the shape of openings on d* is also ofinterest. We measured the flame extinction size of rectangular openings with aspect ratios (b/a) of 3 and 5 andgeneralized the extinction size by introducing the effective diameter (d eff ), which may be taken as the hydraulicdiameter:d eff ≡ 4 A P ,(6.9)

where A is the cross-sectional area of the opening and P is the perimeter of the opening. For a circle, d eff = d.
Figure 6.16 shows the results of 21 vol% R32/air using rectangular openings and circular openings as a function of h.
The results of the rectangular openings agreed with those of the circular openings, which validated the introduction of
the hydraulic diameter. Thus, we can generalize the extinction diameter of openings.

69Effective diameter (deff), mm

Circular, Go

8

Circular, No go

7

Rectangular, b/a=3, Go
Rectangular b/a=3, No go

6

Rectangular b/a=5, Go
Rectangular b/a=5, No go

5
4
3
2
0

10

20

30

40

50

60

h, mm

Figure 6.16: d eff versus h for R32/air measured with various openings. Circle: circular opening. Square: rectangularopening with b/a = 3. Triangle: rectangular opening with b/a = 5. Filled symbols represent “go,” and open symbols
represent “no go.”Consider the application of d*. Figure 6.17 compares the extinction diameters of several refrigerants with the openingsof the electrical components. At h = 9 mm, the flame of propane could go through the opening with d = 1.25 mm. On
the other hand, the flame of R32 could not go through the opening with d = 5.5 mm. This indicates that, if ignition
occurs inside an electrical component, the propane flame will easily go through the small opening of the equipment andpropagate outside the component, whereas the R32 flame will not go through the opening and will be extinguishedwithin the component enclosure. If we measure h and d eff of an electrical component and the combination of h and d eff
lies below the d* curve of the refrigerants, as shown in Figure 6.15, the flame will not go through the opening.
Otherwise, it will be necessary to change h and/or d eff of the component for safety reasons until the combination falls
below the d* curve in Figure 6.15.

Figure 6.17: Comparison of extinction diameters (at h = 9 mm) with openings of electrical components.

6.3.3 Incendivity test using practical electrical components
An incendivity test was carried out by using a magnetic contactor (MC) connected with a high power load. The target
refrigerants were R32 and R1234yf. Figure 6.18 shows the experimental apparatus and the MC inside the combustion
vessel, which was connected with the motor. First, we removed the lid of the MC (blue part of Figure 6.18 (7)) andobserved whether ignition occurred with the spark generated by disconnecting the MC. The spark energy was70approximately 4 J or lower, which is usually higher than the E min of the refrigerants listed in Table 6.3. In more than 300
trials, we observed only a single ignition for R-32. For R1234yf, we did not observe any ignition. With the lid, no flame
propagation was observed for R32 and R1234yf. This result may be rationally explained by the larger extinction
diameter of these refrigerants than the size of the opening of the MC.

Figure 6.18: Experimental apparatus of incendivity test using magnetic contactor.
(1) Motor, (2) Loader using powder brake, (3) Load controller (power supply), (4) Slidac (voltage transformer, 200 and
220 V), (5) Cooling blower, (6) Cylindrical vessel (I.D. = 310 mm, L = 310 mm, V = 24.3 L)(7) Magnetic contactor(65 A rating)

6.3.4 Summary of ignition energy evaluation
Based on the above experimental results, we found the following:- 2L refrigerant compounds with S u0,max below 10 cm s-1 have E min that is greater than that of propane by more than anorder of magnitude. E min is greater than the spark energy from the human body.
- 2L refrigerants have a quenching distance that is more than three times that of propane. Thus, electrical components
will frequently generate sparks for gaps narrower than d q of 2L refrigerants. In such cases, the conductive heat loss tothe electrodes will significantly increase the energy necessary for ignition of the 2L refrigerant. This may be one of themain reasons why R32 ignition occurred very rarely with a magnetic contactor that had a spark energy that was muchgreater than the E min of R32.
- 2L refrigerants have a flame extinction diameter several times larger than that of propane. Even though there are small
openings on the enclosures of potential igniters such as magnetic contactors and sockets, the flame of 2L refrigerants
cannot go through the openings, and such igniters will not become an ignition source of the refrigerant.

References
Lewis, B., Von Elbe, G., 1987, “Combustion, Flames and Explosions of Gases”, Third ed., Academic Press, New York,
p. 333-361.

71

7. Physical Hazard Assessment on Explosion and Combustionof A2L Class Refrigerants
Difluoromethane (R32, CH 2 F 2 ) and 2,3,3,3-tetrafluoropropene (R1234yf, CH 2 =CFCF 3 ) have zero ozone depletion
potential (ODP) and low global-warming potential (GWP). In particular, R1234yf has a low GWP of less than 150, as
established by EC (2012); thus, these two compounds are expected to be the next generation of refrigerants. Althoughthese refrigerants perform better than existing refrigerants in terms of lower ODP and GWP, they exhibit a mild
flammability. Thus, evaluating the combustion safety of A2L refrigerants in the event of leakage into the atmosphere
due to an accident is necessary. To address the issue of global warming due to conventional refrigerants, ASHRAE(2010) defined the optional Class 2L to classify refrigerants with lower flammability and is preparing to promote theconversion of air-conditioning equipment from conventional refrigerants to the next generation of refrigerants. In thisstudy, the experimental flammability of gases such as R32 and R1234yf was analyzed by using a large spherical
combustion vessel to evaluate their fundamental flammability characteristics and assess their safety. Flammability
properties such as the flame velocity, burning velocity, and deflagration index were evaluated. The effects of flame
lifting due to buoyancy and humidity on the flammability characteristics were considered. A numerical simulation andcombustion model were developed to estimate the potential risk of combustion and explosion in actual situations, andthe autoignition temperature of A2L/2L refrigerants was determined.

Symbols

Greek

dP/dt

rate of pressure rise (100 kPa/s)φequivalent ratio

KG

deflagration index for gases (100 kPa m/s2)

ρdensity (kg/m3)

Ppressure (100 kPa)

P red

reduced maximum puressure

Subscripts(as a result of venting)uunburned gas

3

V vesselvolume of the vessel (m )bburned gas

Ttemperature (K)0at standard temperature and pressure/at initial

Sfflame speed (cm/s)

Suburning velocity (cm/s)tcondition

time (s)maxmaximum value

μg

under micro gravity

7.1 Combustion and explosion assessment for A2L/2L
To utilize these mildly flammable gases safely, ASHRAE (2010) added the optional 2L subclass to the existing Class 2(lower flammability) to classify the safety of refrigerants. R32 and R1234yf are classified as A2L refrigerants, which
are defined as having low toxicity and low flammability with a maximum burning velocity of ≤10 cm/s. A2L
refrigerants have such a low burning velocity that a lifted flame front due to buoyancy significantly affects their
combustion behavior. In terms of safety, investigating the fundamental flammable properties of these alternativerefrigerants is important. In this study, a large-volume spherical vessel was prepared to observe and evaluate the effectof buoyancy on the flammable properties of R32 and R1234yf; the flame propagation behaviors of these two
refrigerants were observed using a high-speed video camera. The flame propagation velocity was estimated by image

72

analysis of the high-speed video images. The burning velocity was estimated from the flame speed and the pressure
profile; the latter was measured using the spherical vessel method under the assumption of a spherical flame front
expansion (Takizawa et al., 2009). The maximum peak pressure (i.e., maximum overpressure relative to the pressure in
the vessel during combustion) and deflagration index (i.e., constant that defines the maximum rate of pressure increase
with time of combustion as defined by ISO 6184-2 (1985) and NFPA68 (2007)) were evaluated according to thepressure profile. Ignition tests using mixture gases with an electric discharge were conducted for a varying equivalentratio φ, which is the ratio of the fuel–oxygen ratio to the stoichiometric fuel–oxygen ratio: φ0.8−φ1.2 for R32 and
φ1.2−φ1.4 for R1234yf. In the current fiscal year, the flammability in the presence of moisture and elevatedtemperatures was investigated based on concern over the summer season, and the burning behavior at ignition wasinvestigated. An evaluation scheme for the potential risk of combustion and explosion in actual situations wasdeveloped from the experimentally obtained K G values.

7.1.1 Experiment
Figure 7-1 shows the experimental apparatus with the spherical vessel. The spherical vessel had a diameter of 1 m andvolume of 0.524 m3. A pressure transducer was placed on top of the vessel. The pressure profile formed during
combustion was recorded by a data logger. The burning behavior was observed with a high-speed video camera througha PMMA viewing port. The R32 burning behavior was investigated at equivalent ratios of φ0.8–φ1.2. The R1234yf
burning behavior was evaluated at equivalent ratios of φ1.2–φ1.4 against a reference ratio of φ1.325 (mixing ratio of 10
vol%, which Takizawa et al. (2009) reported as giving the maximum burning velocity for R1234yf when using thespherical vessel method (Metghalchi and Kech, 1980 and Hill and Hung, 1988)). Pressure transducers were used to
introduce fuel gas into the vessel up to a certain partial pressure (BGs in Figure 7.1). Air was then introduced into thevessel until the total pressure in the vessel was conditioned at an atmospheric pressure of 101,325 Pa. For the gas
introduction and mixing procedure, gas circulation was maintained by a diaphragm pump (DP in Figure 7.1) during thefuel introduction into the vessel. The electrode for the electric spark was a set of horizontally opposed tungsten wires
that were 1 mm in diameter; the gap length between wires was 7 mm. The vessel was equipped with a jacketed mantle
heater that covered the entire area of the vessel to maintain the operating temperature of the vessel (Figure 7-1, right
picture). The electrode wire was changed to 0.3 mm in diameter to avoid heat loss and structural disturbance. The
electrode provided a spark upon the application of a high-voltage power supply to ignite the mixture gas. The discharge
voltage and current were recorded by an oscilloscope, and the discharge energy was estimated. The flame front
expansion behavior was recorded by the high-speed camera, and the recorded video image sequences were visually
analyzed; the flame velocities in the side and upper directions were evaluated.

Figure 7-1: Schematic drawing and picture of experimental apparatus.

737.1.2 Flame velocity and burning velocity
Image observation
Figure 7-2 shows example high-speed video images for the flame front propagation behaviors of R32 φ0.9 and φ1.2.
The flame expanded while slowly climbing upward. The shape of the flame front, which is the interface between the
unburned and burned gas, was distorted under the influence of buoyancy and viscosity. The expansion behaviors
between φ0.9 and φ1.2 were almost the same other than their temporal response. The left picture in Figure 7-3 shows
high-speed video images for the flame front propagation behavior of R1234yf φ1.35. No clear and smooth flame front
was observed; the flame front was convoluted without symmetry and floated upward. Furthermore, the ignition
characteristics of R1234yf were unstable and depended on not only its flammability but also experimental conditions
such as the discharge energy, duration of discharge, and electrode geometry. Because it was difficult to examine thepossibility of these effects, alternatives such as a small spherical vessel (30 L) and compact elongated cylindrical vessel(10 cm in inner diameter and 20 cm in length) were prepared to investigate the flammable behavior at ignition. The
right picture in Figure 7-3 shows the test results for the compact elongated vessel. A smooth and clear flame front wasobserved that could not be seen in the large and small spherical vessels. The relation between the fluid dynamics fromthe high temperature produced by the burned gas and buoyancy and the slow burning velocity at the bottom of the flame
resulted in the squeezed flame front shape. The flammability of the mixture gas in the closed vessel was affected by not
only the fuel/air mixture ratio, initial pressure, and initial temperature but also the vessel size and shape, ignition source,and other factors. These results suggest the influence of the small vessel volume and shape; thus, the effect of fluid
dynamic behavior on flammability must be considered in scaled-up situations.

400 ms

300 ms200 msR32 φ0.9

100 msR32 φ1.2

Figure 7-2: Images of flame front propagation for R32 (φ0.9 for left, φ1.2 for right).

74

400 ms 200 ms

300 ms 150 ms

200 ms 100 ms

100 ms
50 ms
Figure 7-3: Images of flame propagation for R1234yf(φ1.35, left: large spherical vessel; right: compact elongated vessel).
Figure 7-4 shows pressure profiles for R32 φ0.8–1.2 as measured by a pressure transducer. The profiles all seemed toshow that the pressure increased in stages. A possible cause may be the influence of the reflected flame front from the
top wall. The arrival time of the upper direction flame front to the top of the vessel could be predicted from image
analysis: about 0.5 s for φ0.9 and 0.46–0.47 s for φ1.0–1.2. Thus, the pressure reached a peak maximum far behind thearrival time of the flame front. The flame front rose in the upper direction owing to buoyancy, whereas the unburned gas
remained in the lower half of the vessel. The underside of the flame front was accompanied by a complicated flow of
unburned gas.
Pressure profiles for R1234yf were also measured; these are shown in Figure 7-5. The profile trends associated with theequivalent ratio were not simple. This seems to be due to the influence of the unstable ignition characteristics. The
pressure increased to the peak maximum very gradually compared with R32 and took more than 6 s. The profile for thepressure increase at φ1.35 was small, and no increase in pressure was observed at φ1.4; therefore, most fuels seemed toremain without burning.

Flame speed and burning velocity
The maximum flame width and flame top position from the ignition point were visualized for R32, and the flame speed
S f was estimated based on the temporal differentiation of the flame width and height of the flame top profile. The flame
speeds in the upper direction increased 1.2–2.0 times more than those in the side direction as time progressed, owing tobuoyancy associated with the increase in volume of the burned side. For R1234yf, proper evaluation of the maximum
flame width and flame top position was difficult because a clear and smooth flame front was not observed.
The burning velocity S u was evaluated from the flame speed S f (Pfahl et al., 2000) as follows:75

(7-1)
where ρ is the density (m-3) and subscripts u and b of ρ denote unburned and burned gas, respectively. ρ u is the density
at the initial condition, and the unknown ρ u density was estimated using the chemical equilibrium calculation developedby Gordon and McBride (1994) under the assumption of a constant pressure during combustion. S f is the flame speed(cm s-1). In this study, the upward flame speed S f was estimated from the rate of change in the flame top position (cm)with time along with the sideward flame speed S f , which was estimated from the rate of broadening of the half-flame
width r f (cm) (Pfahl et al., 2000). The sideward S f minimizes the influence of buoyancy, whereas the upward S f
involves the apparent speed due to buoyancy. The burning velocity S u was also calculated by the spherical vessel
method (Metghalchi and Keck, 1980, and Hill and Hung, 1988 ) under the assumption of a spherical flame front
expansion as follows:(7-2)

where R is the inner radius of the chamber (m), x is the mass fraction of burned gas, P 0 is the initial pressure in thechamber (Pa), P is the instantaneous pressure during burning in the chamber (Pa), and γ u is the specific heat ratio. The
values of x and γ u for each instantaneous pressure were estimated using the equilibrium code (Gordon and McBride,1994).
As shown in Figure 7-6, the burning velocity S u was estimated by using the sideward flame speed S f for R32. The
burning velocity according to the spherical-vessel (SV) method was also estimated from the obtained pressure profiles
and numerical computation under the assumption of spherical flame propagation for R32, as shown in Figure 7-6.
Although the flame did not propagate with a spherical shape, as shown by the high-speed video images presented in
Figure 7-2, S u0 was estimated and used to investigate the deviation due to distortion from buoyancy. During analysis,
the pressure increase profile did not depart from the scope of the spherical flame front expansion in the early stages. S u0
was compared with the reference S u0 values for R32 (Takizawa et al., 2005). The burning velocities based on the flame
speed and SV method showed similar equivalent ratio dependencies, but the SV method slightly underestimated S u0 . As
shown in Figures 7-3 and 7-5, the flame front expansion was convoluted except for φ1.325, and applying the SV
method was difficult. Therefore, the burning velocity S u0 was estimated for R1234yf φ1.325 only; this is shown in
Figure 7-7. For R1234yf, the buoyancy had a particular influence on the flame expansion behavior. Takizawa et al.
(2010) estimated S u0-ug for R1234yf under a microgravity environment, and it is shown as a reference in Figure 7-7.

Figure 7-4: Pressure profile for R-32 (φ 0.8–1.2).

Figure 7-5: Pressure profile for R-1234yf (φ 1.2-1.35).

76

Figure 7-6: Estimated burning velocity for R-32.

Figure 7-7: Estimated burning velocity for R-1234yf.

7.1.3 Effect of moisture
Kondo et al. (2012) have reported the effects of temperature and humidity on the flammability limits of some A2L/2L
refrigerants; this is an important issue, especially with the hot and humid climate of Japan. Temperatures of over 30 °C
and 80% humidity are often recorded in the summer. To control the humidity in the mixture gas, the dew-pointtransmitter MICHELL SF72 was used to measure the dew point in the chamber and set in the circulation loop, as shownin Figure 7-1. The moisture was added to the mixture gas on the circulation loop by a bubbler. The humidity of the
mixture gas was evaluated according to the dew point (dp) and temperature. In the experiment, about 56% RH was
attained at the given temperature of 30 °C.
Flammability tests were conducted under dry (10–30 °C) and wet (60% RH at 30–35 °C) conditions for R32 at φ1.1 andfor R1234yf at φ1.325 (Saburi et al., forthcoming). With the addition of the moisture and elevated temperature, R32
exhibited a flammable process with almost the same flame front shape as under the dry condition, and R1234yf showeda relatively clear flame front shape compared with the dry condition. A blue flame was observed for R1234yf under thedry condition, but a luminous flame was observed under the wet and elevated temperature conditions. These results arebeing prepared for publication, and the effects of moisture and temperature on the flammable behavior of R1234ze arealso under investigation.
Research on the effect of buoyancy on the flammability behavior that considers humidity will continue to be conducted.

7.1.4

Deflagration index, K G value

The deflagration index K G was estimated to analyze the recorded pressure profiles. K G is commonly used to estimate
and design the explosion venting area of enclosures; it is defined by ISO6184-2 (1985) and NFPA68 (2007) and is
described in the following equation(7-3)
where P is the pressure (100 kPa), t is the time (s), and V vessel is the volume of the vessel (m3). A larger K G requires alarger venting area to prevent the enclosure from bursting. Table 7-1 summarizes the deflagration indices for gases K Gof each refrigerant along with other properties such as P max , S f , and S u . The physical interpretation that K G isdetermined after the reflection of the flame front at the top wall must be considered, but the evaluated values may be
useful for designing the venting area.
Table 7-2 lists P max and K G with other major gases in descending order of K G . The table indicates that K G values for
R32 and R1234yf were considerably small and the same as or less than that for ammonia (i.e., 10) given in NFPA68

77

(2007). The results of the evaluated fundamental flammability characteristics will be expanded in scale for application
to flammable behavior at actual scales, and an evaluation scheme for the potential risk of combustion and explosion in
actual situations will be considered.
Table 7-1: Summary of evaluated properties for refrigerants.

a Ref. (Takizawa et al., 2005)b Ref. (Takizawa et al., 2010), Obtained data under micro-gravity (S u0-ug ).

7.2 Numerical simulation for combustion of A2L/2L
To apply refrigerants safely to air-conditioning equipment, the potential risk of combustion and explosion in actual
situations should be evaluated by using the results of the laboratory-level fundamental evaluation. The relationshipbetween the deflagration index and the influence on human and structures was considered with the help of the conceptof vent design using K G values. For example, the reduced effect of the pressure due to an aperture in the room can beevaluated based on vent design. It is difficult to address a variety of evaluation endpoints, such as the installation
configuration of air-conditioners, accident conditions, and the scale of leakage, by means of experimental measures, but
a numerical simulation is an effective method. First, a non-reactive numerical simulation can be performed to reproduce
the experimental results in the large spherical vessel and evaluate the effect of the reduced pressure rise (P red ) if anaperture exists in the vessel. Then, the capability of evaluating the reduced effect due to an aperture in the actual room
can be reviewed according to the design scheme described in NFPA68 (2007). A numerical combustion model for
A2L/2L−air premixed gases should be constructed, and the development of a computational fluid dynamics (CFD) code
incorporated with the combustion model will enable the combustion behavior of refrigerants under various conditions tobe simulated to help estimate the flame propagation distance and blast pressure. The combustion model can be validated
by simulating and reproducing the combustion behavior in experiments. The basic concept of the combustion model isbased on Zimont (2000); it is the solution to a transport equation for the variable c with regard to the degree of reaction
progress using a function for the burning velocity S u . The burning velocity is obtained as a time-dependent variable byanalyzing experimental data obtained during the project and is believed to be a laminar flame based on the current
results. On a practical scale, there is concern over some deviations from the experimental results due to various
instabilities, especially those resulting from the effect of buoyancy. Development of a model that considers these factors
is in progress.

787.3 Combustion and explosion of A2L/2L by excess energy
7.3.1 Estimation of potential risk of explosion
To achieve practical application of A2L/2L refrigerants and enhance safety, the potential risk of explosion, including
detonation, should be considered. At present, there have been few reports on this matter. As an implicit but usefulreference, a comparison of explosion characteristics such as the minimum ignition energy (MIE), detonation limit, andK G with other flammable gases should be very informative. Table 7-2 lists flammable parameters such as P max , K G ,burning velocity, and flammability and detonation limits for mixtures with air that were taken from Mannan (2005).
P max and the burning velocity appear to have the same tendency as K G . Further comparison for the combustion andexplosion risks of A2L/2L refrigerants with other flammable gases should be considered.
Table 7.2: Comparison of P max , K G and other parameters with other gases.

*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 † This work.

7.3.2 Autoignition temperature
The autoignition temperature (AIT) is the lowest temperature at which a flammable substance will ignite in air at
normal atmospheric pressure without an external energy supply such as a spark or flame. To estimate the autoignition
characteristics of A2L/2L refrigerants, a test will be conducted according to the ASTM E 659 standard test method(ASTM, 2005). This method determines the autoignition temperature of liquid chemicals in air or solid chemicals thatreadily melt and vaporize at temperatures below the test temperature in a uniformly heated vessel at atmosphericpressure. We will employ this method for flammable gases in the presence of moisture; some metals will used as
catalysts.
The test equipment, which has an operating temperature range of up to 1000 °C, is shown in Figure 7-8; it will be
operated in open air, so an abatement system for toxic product gas is under construction. The test of refrigerants using
this system will be performed soon. The autoignition characteristics of A2L/2L refrigerants and other flammable gases
such as propane and ammonia will be compared.

79Figure 7-8: ASTM E659 autoignition test equipment.

7.4 Conclusion
To evaluate the fundamental flammability characteristics of A2L refrigerants and assess the safety of their use,
flammability properties such as the flame velocity, burning velocity, and deflagration index were evaluated. The effectsof flame lifting due to buoyancy and humidity on the flammability characteristics were considered. A numericalsimulation and combustion model were developed to estimate the potential risk of combustion and explosion in actual
situations and determine the autoignition temperature of A2L/2L refrigerants. Physical hazards with regard to the
explosion and combustion of A2L class refrigerants were evaluated. Flammability characteristics such as the flame
speed, burn velocity, K G value, and peak pressure were evaluated in a premixed gas combustion test; the effects ofbuoyancy and moisture were considered through numerical simulation. To assess the explosion risk of A2L/2L
refrigerants, the burning velocity and detonation limits were compared with those of other flammable gases.

References
American Society for Testing and Materials, 2005, Standard Test Method for Autoignition Temperature of Liquid
Chemicals, ASTM E 659−78.
ASHRAE, 2010, Designation and Safety Classification of Refrigerants, ANSI/ASHRAE Standard 34-2007 Addendum
ak.
European Commission, 2012, Proposal for a Regulation of the European Parliament and of the Council on Certain
Fluorinated Greenhouse Gases, COM (2012) 643 final.
Gordon, S., and McBride, B. J., 1994, Computer Program for Calculation of Complex Chemical Equilibrium
Compositions and Applications, I. Analysis, NASA RP-1311.
Hill, P. G., and Hung, J., 1988, Laminar Burning Velocities of Stoichiometric Mixtures of Methane with Propane andEthane Additives, Combustion Science and Technology, 60, pp.7–30.
ISO 6184-2, 1985, Explosion Protection Systems– Part 2: Determination of Explosion Indices of Combustible Gases inAir, (1985).
ISO/DIS 817, 2010, Refrigerants: Designation and Safety Classification, International Organization for Standardization,
Geneva, Switzerland, (current DRAFT DFS/ISO/FDIS 817:2012).

80

Japan Fluorocarbon Manufacturers Association, 2013, Environmental and Safety Data List of Specified Fluorocarbons(CFC/HCFC) and Other Fluorocarbons (in Japanese), URL: http://www.jfma.org/database/table.pdf (2013), 31 Feb.
2014 .
Kondo, S., Takizawa, K. and Tokuhashi, K., 2012, Effects of Temperature and Humidity on the Flammability Limits ofSeveral 2L Refrigerants, Journal of Fluorine Chemistry, 144, pp. 130–136.
Mannan, S., 2005, Lee’s Loss Prevention in the Process Industries, 3rd ed., Elsevier, 2, p.1383.
Metghalchi, M., and Keck, J. C., 1980, Combustion and Flame, 38, pp. 143–154.
NFPA, 1994, NFPA 325 Guide to Fire Hazard Properties of Flammable Liquids Gases, and Volatile Solids, NFPA.
NPFA, 2007, Guide for Venting of Deflagrations 2007 Edition, NPFA 68, (2007).
Pfahl, U. J., Ross, M. C., and Shepherd, J. E., 2000, Flammability Limits, Ignition Energy, and Flame Speeds in
H2−CH4−NH3−N2O−O2-N2 Mixtures, Combustion and Flame, 123, pp. 140–158.
Saburi, T., et al., forthcoming, Flammable behaviour of A2L refrigerants in the presence of moisture, 10th ISHPMIE,
Bergen, #110.
Takizawa, K., et al., 2009, Flammability Assessment of CH2=CFCF3: Comparison with Fluoroalkenes andFluoroalkanes, Journal of Hazardous Materials, 172, pp. 1329–1338.
Takizawa, K., Takahashi, A., Tokuhashi, K. Kondo, S., and Sekiya, A., 2005, Burning Velocity Measurement of
Fluorinated Compounds by the Spherical-Vessel Method, Combustion and Flame, 141, pp. 298–307.
Takizawa, K., Tokuhashi, K., Kondo, S., Mamiya, M., and Nagai, H., 2010, Flammability Assessment of CH2=CFCF3(R-1234yf) and its Mixtures with CH2F2 (R-32), 2010 International Symposium on Next-generation Air
Conditioning and Refrigeration Technology, Tokyo, P 08.
Zimont, V., 2000, Gas Premixed Combustion at High Turbulence: Turbulent Flame Closure Combustion Model,
Experimental Thermal and Fluid Science, 21, pp. 179–186.

81

8. Efforts of the Japan Refrigeration and Air Conditioning Industry Association
8.1 Progress by Mini-Split Risk Assessment SWG
8.1.1 Outline of Mini-Split Risk Assessment SWG
The mini-split risk assessment SWG considered a 2.2–8 kW small business–use air conditioner mounted on a wall. Small
business–use air conditioners are equivalent to residential air conditioners. A risk assessment of residential-use multi-split type air
conditioners, where two or more indoor units are installed for one outdoor unit, was also started last year. The SWG worked on
the risk assessment of floor-standing type small air conditioners of 8 kW or less for households. Figure 8.1.1 shows the installationof wall-mounted and floor-standing residential air conditioners.
In order to carry out the risk assessment of one-to-one air conditioners in stores (3.6–25 kW), a mini-split risk assessment SWG (II)was formed. The SWG (II) promoted risk assessment by collecting experts on various components.

Fig 8.1.1 Indoor space

Fig 8.1.2 Risk map

This interim report describes the risk assessment results for the following.
(1) Wall-mounted type 2.2 kW mini-split air conditioner using R32 and R1234yf (residential and small business–use air conditioners).
(2) Floor-standing type 2.8 kW air conditioner using R32.
(3) One-to-one 7.1 kW ceiling installation air conditioners for stores using R32.
A risk assessment was carried out on multi-unit air conditioners for home use; there were no practical problems, but there wereregulatory problems.

8.1.2 Risk assessment procedure
Alternative refrigerants for use in mini-split air conditioners, such as R32 alone or R32 refrigerant mixed
with R1234yf and R134a, have been proposed to prevent global warming. Naturally, these proposed refrigerants do not destroy theozone layer. The mini-split risk assessment SWG flagged safety as a potential problem with using these refrigerants, and studies were
performed to plan countermeasures. A risk assessment was performed to compare R290, as a representative naturalrefrigerant, with R32 and R1234yf. The risk assessment then evaluated the presence of ignition sources and flammable regions. Yao
and Kataoka (2000) performed a risk assessment of a room air conditioner using propane to calculate the probability of ignition
sources and flammable regions materializing simultaneously by fault tree analysis (FTA).
The flammability hazard of changing from a conventional air conditioner to one using a mildly flammable refrigerant wasevaluated. Risk assessment techniques have changed since 2000; the handbook from the Ministry of Economy, Trade and Industry(2011) was referred to as much as possible. In order to judge the safety, we referred to the risk map presented in Figure 8.1.2 in82

particular.

8.1.3 Ignition sources
If the R32 refrigerant used in a mini-split air conditioner leaks to the environment, a flammable atmosphere can form in rare cases. In
that case, sparks from electrical equipment, metal collision, and static electricity or the open flame of combustion equipment such as
oil stoves are assumed to be ignition sources. In addition, smoking objects can ignite oil and gas by a spark to produce an open
flame. These ignition sources were examined in detail in the 2011 and 2012 progress reports of the Japan Society of Refrigerating and
Air Conditioning Engineers. The SWG referenced the reports by Imamura et al. (2012), Takizawa (2011), and Goetzler et al. (1998)
to describe the following items assumed to be ignition sources:(1) An electromagnetic contactor with no cover ignites at 7.2 kVA or more. However, if a contact is covered with a clearance of 3
mm or less, it does not ignite until 12 kVA or more. Low-voltage electrical equipment in Japanese homes almost never ignites.
(2) R32 is not ignited by burning tobacco that does not emit a flame.
(3) Static electricity caused by humans in a living space almost never cause ignition.
Based on the above considerations, the ignition sources of outdoor and indoor mini-split air conditioner units using R32 or R1234ywere assumed to be open flame in the risk assessment. Note that the ignition sources of store air conditioners, which have a
different environment, are described separately.

8.1.4 Results for Flammable Region
8.1.4.1 Flammable Space
The flammable space assumed in this risk assessment was the same as the space described by Yao et al. (2000). As an indoor spacewith an air conditioner was the most important consideration in the risk assessment, a small room with a floor area of 7 m2 and heightof 2.4 m was used for the leakage space. The installation position of the indoor wall-mounted type unit was set at a height of 1.8 m
from the floor, and the floor-standing type unit was set on the floor. Figure 8.1.1 shows a schematic diagram of the installation
conditions of the air conditioner.
A semi-fireproof warehouse was constructed as per the Building Standard Law. In order for the warehouse to be considered narrowand high-risk, the capacity was set to 1000 m2, and it was assumed to store 10,000 air conditioners.

8.1.4.2 Generation of Flammable Region
Generating the flammable region is important to the risk assessment of mildly flammable refrigerants. Values for R32 and R1234yf
were obtained using the same technique developed by Yao et al. (2000), and the simulation was performed at the University of Tokyo.
Table 8.1.1 presents the flammable time volumes used in this risk assessment.
Table 8.1.1 Flammable time volumes in leakage situations(m3·min)
1.1 Logistics
2.2 Installation
2.5 Mistakes
2.10 refrigerant charge
3.1 Indoor unit operation
3.5 Indoor unit stop
4.1 Outdoor unit
5.1 Connecting pipe
7.8 Service/relief
8 Disposal

R290
R32
R1234yf
5.50 × 101
2.00 × 10-4
2.20 × 10-4
2
-3
7.16 × 10
2.40 × 10
2.50 × 10-4
-2
-3
7.75 × 10
9.00 × 10
1.30 × 10-2
3
1
8.51 × 10
9.97 × 10
3.70 × 102
1-4
1.41 × 10
5.00 × 10
5.50 × 10-4
3-2
7.16 × 10
2.40 × 10
2.50 × 10-2
-1-2
7.76 × 10
9.00 × 10
1.30 × 10-1
3
2
8.51 × 10
9.97 × 10
3.70 × 103-2-3
7.75 × 10
9.07 × 10
1.30 × 10-2
Using similar situations and values

838.1.5 Questionnaire of Installation and Service
A questionnaire on refrigerant leakage and the use of fire during installation and service was sent by the JRAIA to construction
vendors and service shops, and nearly 600 replies were received. The incidence of refrigerant leakage or fire use is as follows.
The incidence of refrigerant leakage at installations was 0.74%, which is comparable with the incidence of 0.77% during service.
However, refrigerant leakage increased during charging and recovery. Small amounts of leakage may occur when a worker detaches
and attaches a charge hose and connection joint. The reported refrigerant leakage may be 1/100 of the actual value. With respect to fireuse, the amount of smoking during service was 1.3%, and other types of fire use were 4.2%. During service, pipes may sometimes
need to be welded, so the use of fire sources such as burners or ignition lighters for a burner was assumed, which should increase therate of fire usage.
Smoking is discussed later.

8.1.6 Results of Risk Assessment
8.1.6.1 Major Accident Probability
According to NITE, a home appliance has a major accident probability of 10-8 sets/year (base of 1 million sets). In other words,
a product with one million units distributed a year is considered safe if a fatal accident occurs once in 100 years. The total number ofmini-split air conditioners and residential air conditioners in Japan is about 100 million sets, so the target value in the FTA calculation
was set to ≤10-10 sets/year.

8.1.6.2 Outline of Risk Assessment Results
Table 8.1.2 presents the current risk assessment results for the strongly flammable R290 refrigerant and mildly flammable R32 andR1234yf. The risk was estimated for each step of the refrigerants’ life cycles: logistics, installation, use, service, and disposal. We
decided that each company managed the production step individually.
The ignition probabilities of R32, R1234yf, and R290 were 2.1 × 10-12, 2.2 × 10-12, and 5.9 × 10-9–1.1 × 10-4, respectively. The
probabilities for R32 and R1234yf were generally smaller than the target value, and so they were considered to be safe. However, theignition probabilities for R32 and R1234yf were 1.2 × 10-6 and 2.5 × 10-6, respectively, during the logistics and service steps. These
values are larger than the target value, so we considered the need for countermeasures. The target value is the value required by users
when all of the hazards in the risk map of Figure 8.1.1 are assumed to lead to a fatal fire accident.

Logistics
Installation
Use (Indoor)(Outdoor)
Servicedisposal

Table 8.1.2 Current risk assessment results
Risk: Ignition Probability
R290
R32
1.9 × 10-8–4.9 × 10-6
1.7 × 10-10
1.5 × 10-6–1.7 × 10-5
1.2 × 10-6
-9-4
5.9 × 10 –1.1 × 10
2.1 × 10-12-13-8
9.7 × 10 –1.9 × 10
8.4 × 10-10-6-5
9.3 × 10 –1.7 × 10
2.6 × 10-9-5-4
1.8 × 10 –1.3 × 10
5.3 × 10-11

R1234yf
1.9 × 10-10
2.5 × 10-6
2.2 × 10-12
1.2 × 10-9
2.8 × 10-9
7.8 × 10-11

The mini-split risk assessment SWG referred to target values from reports published in 2011 and 2012, so the values were slightly
different. This can be a factor because the latest fire statistics should be considered when reviewing ignition sources. Outdoor use
involves the installation of a fence (i.e., decorated enclosure for outdoor unit) and the installation of multiple air conditioners on anapartment veranda.

8.1.6.3 Reexamination of Risk Assessment Result
The risk assessment was reviewed to reflect on recent findings. In particular, an FTA of smoking as the dominant ignition source was84reviewed. According to a study by the Tokyo University of Science (Suwa), mildly flammable refrigerants such as R32 do not ignitefrom the fire from tobacco and piezoelectric lighters.
In addition, lighters are used for shorter durations of time than the time taken to smoke tobacco. The FTA was revised to consider
time: e.g., percentage of lighter operation time relative to smoking time and percentage of smoking time. In addition, the ignition
source percentage of the flammable region was added. This was confined to ignition by a match or oil lighter.
The FTA was reviewed for each step of the life cycle (i.e., logistics, installation, use, service, and disposal), and the new findings wereas described above. Table 8.1.3 presents the results of the risk assessment review.

Logistic
Installation
Use (Indoor)(Outdoor)
Servicedisposal

Table 8.1.3 Results of risk assessment review
Risk: Ignition Probability
R290
R32
9.2 × 10-11–1.4 × 10-7
4.1 × 10-12
3.7 × 10-9–2.2 × 10-8
2.7 × 10-10-13-95.0 × 10 –9.5 × 10
3.9 × 10-15-13-9
4.9 × 10 –9.3 × 10
1.5 × 10-10-7-7
2.8 × 10 –8.1 × 10
3.2 × 10-10-7-7
4.1 × 10 –5.1 × 10
3.6 × 10-11

R1234yf
4.5 × 10-12
3.1 × 10-10
4.3 × 10-15
2.1 × 10-10
3.6 × 10-10
5.3 × 10-11

The ignition probability of indoor units was considerably less than the target value of 10-10 units/year derived from domestic air
conditioners using R32 and R1234yf. These values were not considered to pose any problems. However, the ignition probabilities ofoutdoor units using these two refrigerants were 1.5 × 10-10 and 2.1 × 10-10, respectively, which are slightly larger than 10-10 units/year.
These FTA values assumed the hazard degree of severity to lead to a fatality (IV) according to the matrix of the risk map. However, a(IV) degree of severity for ignition in an open space such as outdoors needed to be verified.
The highest ignition probabilities were during service at 3.2 × 10-10 and 3.6 × 10-10, respectively. The installation step also
showed similar values. The probabilities during service and installation were higher than the target value of 10-10 units/year. However,the service and installation steps are performed by trained professionals who follow instructions or manuals with care andresponsibility. We believe that the target values can be increased to 10 times from 1000 times to ensure safe use by professionals. Thus,
the ignition probabilities during the service and installation steps are not a problem in practice.

8.1.7 Risk assessment of Floor-Standing Type Air Conditioners
8.1.7.1 Installation Patterns and Issues with Floor-Standing Type Air Conditioners
There are several indoor unit types of mini-split air conditioners other than the wall-mounted type; each requires a specific risk
assessment based on the connection specifications and installation method. Figure 8.1.3 compares the installation patterns of ordinary
air conditioners and multi-connection type mini-split air conditioners for residential use. Other types of residential air conditioners
include floor-standing, ceiling-mounted cassette, wall-embedded, and built-in. In the current evaluation, the flammable refrigerant was
fluorocarbon-based; it tends to accumulate near the floor because it is denser than air. Therefore, we assumed that floor-standing typeunits have the highest risk among indoor units in the case of a refrigerant leakage. This risk becomes even higher for multi-connection
type residences that require more refrigerant charge than ordinary air conditioners. To avoid confusion, we first explain the risk
evaluation of ordinary floor-standing type air conditioners before moving on to air conditioners for residences.

85

Ceiling-mounted
cassette type

Outdoorunit

Outdoorunit

Ceiling-mounted
cassette type

Wall

Wall
●Considered conditions
Refrigerant: R32(R1234yf for wall-mounted type)
Amount of refrigerant: 1 kg
Installation area: 7 m²

Outdoor
unit

Floor

●Considered conditions
Refrigerant: R32
Amount of refrigerant: 2 and 4 kg
Installation area: 7 m²
Outdoor
unit

Floor

Residential-use multi-split type air conditioners(1 outdoor unit: multiple indoor units)

Ordinary air conditioner(1 indoor unit: 1 outdoor unit)

Fig 8.1.3 Installation pattern and considered conditions for residential-use multi-split type air conditioners

8.1.7.2 Ignition Sources and Combustible Space for Floor-Standing Type Air Conditioners
The ignition sources for floor-standing type air conditioners were assumed to be the same as those for wall-mounted type air
conditioners. The residential space conditions were also taken to be the same as for the wall-mounted type: a small residential roomwith a floor area of 7 m2 and height of 2.4m. The indoor unit was floor-standing. The volume of combustible air space was defined bya simple calculation to adjust the leakage height based on the values in Table 8.1.1.

8.1.7.3 Target Accident Probability for This Risk Assessment
The target accident probability in this risk assessment followed the same idea of NITE for wall-mounted type air conditioners. In
some cases, floor-standing type air conditioners are installed by the same contractors who install residential-use air conditioners, but inmost cases the installation is performed by well-trained professionals. The number of floor-standing type air conditioners in the market
is as little as 1% of wall-mounted type air conditioners. Their specifications and usage are similar to those of package air conditioners
and multi-type air conditioners for buildings; thus, we set the target accident probability during operation (hereafter: target value) to beless than 10-9. However, since the risk level can be lowered by an order of magnitude because of the better awareness of workers who
perform the installation and service work, the target probability was set to less than 10-8. Table 8.1.4 compares the risk assessments ofwall-mounted type mini-split air conditioners and ceiling-mounted cassette type air conditioners to floor-standing type air conditioners
for the various stages of their life cycles.

86Table 8.1.4 Life cycle stages and allowable values (accident probability)

8.1.7.4 Considerations When Reassessing Risks for Floor-Standing Type Air Conditioners
Based on the results of the risk assessment using an FTA of floor-standing type air conditioners, as described above, we found that theallowable ignition probability with no countermeasures was 9.8 × 10-8, which did not meet the target value.
As the refrigerant R32 is generally heavier than air, it tends to accumulate more easily at lower heights. Since the specific height ofignition sources from the floor can be defined, we considered reassessing risks by dividing the air space by the height. Specifically, we
considered the height of each ignition source from the floor in the case of a refrigerant leak inside the residential space. Table 8.1.5 lists
the specific height of each ignition source to demonstrate the particular heights of various human activities from the floor. Although
the most dangerous status is when a person is lying down, we found that other ignition sources are relatively high above the floor.
Table 8.1.5 Specific heights of various indoor ignition sources

Fig 8.1.4 Heights of various life time87

As presented in Table 8.1.5, we also examined the heights of ignition sources for the kitchen and the Japanese-style room to evaluate
particular scenarios of air conditioner use inside a room, since these two spaces generally have many ignition sources. Table 8.1.5
presents various ignition sources and their heights in a kitchen and Japanese-style room. Based on the height from the floor, the highest
risks in a kitchen and Japanese-style room are gas stoves and cigarette lighters, respectively. We reassessed floor-standing type air
conditioners and calculated the height reached by the volume of combustible air space above the floor with a focus on the floor space.
The strictest condition considered was that the entire amount of R32 refrigerant should leak and create an air space with the lowest
possible LFL of the flammable concentration.

8.1.7.5 Risk assessment Results of Floor-Standing Type Air Conditioners
Table 8.1.6 presents the risk assessment results for floor-standing type residential air conditioners.
Table 8.1.6 Results of floor-standing residential air conditioner risk assessment

Type
Logistics(for every storehouse)
Installation
Use (indoor)(outdoor)
Service
Disposal

Risk: Ignition Probability
Representative model
Middle-size storehouse
2

R32
-11

3.6 × 10

4.0 × 10-11
9.9 × 10-10
8.6 × 10-11
2.6 × 10-10
2.5 × 10-11

3.24 m veranda
9.9 m2 room
3.24 m2 veranda
3.24 m2 veranda
3.24 m2 veranda

In particular, Figure 8.1.5 shows the relationship between the floor space (room size) and the ignition probability in the case of arefrigerant leak from a small-size 2.8 kW class floor-standing type air conditioner. We also considered the height of the combustible
space reached above the floor level in the case of an indoor refrigerant leak. Table 8.1.7 describes how the amount of refrigerant
charge and the floor space affect the height that the combustible space reaches above the floor. As presented in Tables 8.1.6 and 8.1.7
and Figure 8.1.5 and considering the relationship between the amount of refrigerant charge and the floor area, we confirmed that theallowable probabilities were lower than 1.6 × 10-9; thus, no countermeasures are needed.
We then considered room sizes of 13–19 m2, which are larger than the initial 7 m2 assumed for floor-standing type air conditioners.
We found that, by limiting air conditioner installation to rooms of more than 10 m2 floor space, the allowable ignition probability
during usage can be met.
For floor-standing type residential air conditioners, we found that the allowable ignition probability in the case of a 4 kg refrigerantleakage from an air conditioner installed in a room with a floor space of up to 13 m2 can be met by using a fan or other method todisperse the refrigerant inside the air. However, according to the current international specifications for air conditioners(IEC60335-2-40), the upper limit of refrigerant charge for a floor-standing type air conditioner installed in a 13 m2 room is 3 kg;
therefore, further examination to ensure safety is necessary.
However, the above installation limitation does not obstruct most installation conditions for general floor-standing type air
conditioners.
Table 8.1.7 Influence of refrigerant amount and floor spaceon height above floor level

1.0E-08

Risk value＜Heights reached above floor level per floor space incase of R32 refrigerant leakage at LFL concentration＞

Floor Space (m2)

1.0E-090

5

10

Allowable level 1.0E-09

1.0E-101.0E-11

Fig 8.1.5 Allowable risk and floor space88

2

Floor space m

床面積×リスク値
1520

Room space applicable for 2.8 kW
capacity is approximately 13–19
2m even in case of wooden houses.

8.1.7.6 Summary of Floor-Standing Type Air Conditioners and Future Development
So far, the mini-split risk assessment SWG had focused on wall-mounted type air conditioners, but the SWG then expanded theassessment target to residential air conditioners in order to accelerate measures to prevent global warming.
All types of residential air conditioners with refrigerant charges of about 1 kg were confirmed to have an ignition probability of 10-9or less (less than 10-8 for workers/during the work step), which was the target value based on the risk assessment with the FTA. As an
example of specific countermeasures, when the air conditioner units were used indoors in limited installation spaces, the ignition
probability of 9.9 × 10-10 was met. For floor-standing type air conditioners (indoor), the installation height was found to have a large
effect on the ignition probability as a risk factor.
Multi-split air conditioners with larger refrigerant charges and severe risk are being compared to one-to-one type residential air
conditioners to evaluate the flammable region and installation space. In order to improve the accuracy of the FTA with regard to
the ignition probability, the SWG is reviewing the height concept with regard to ignition sources and is continuing to study practicalapplications. The SWG will evaluate and confirm the degree of severity of risk with regard to outdoor use in collaboration with
universities and research institutes.

8.1.8 Examination of Unexpected Risk
In the FTA described so far, risks were considered based on common conditions expected at each life cycle step (i.e., logistics,
installation, use, service, and disposal). However, FTA was then performed again for unexpected conditions. We re-extracted
events for conditions that are difficult to forecast. The risk assessment and consideration of these conditions are described in detailin the 2011 and 2012 progress reports of the Japan Society of Refrigerating and Air Conditioning Engineers. We listed the major
points of these reports below:-(1) Conditions outside the expected range that do not happen easily and require very small spaces, a large amount of leakage, and astrong ignition source.

-(2) Conditions where expansion damage is produced with a mildly flammable refrigerant beyond the damage from a natural disastersuch as an earthquake, large fire, or tsunami.

-(3) Conditions where damage is not prevented and human error makes the situation worse.
The SWG members extracted the unexpected risks of 34 events at each life cycle step, and we evaluated each event. Only one of the
34 events was found to influence the FTA: “A home appliance retail store transfers an air conditioner for installation by a minivan,
leakage occurs, the driver lights the cigarette, and the refrigerant is ignited and causes an explosion.” This event was used as theunexpected risk. We studied this risk to improve the FTA and risk is below permissible level..
The FTA outlined in section 8.1.6 provided the correct static values in general for the logistics, installation, use, service, and disposal
steps of the life cycle. Under the assumption of an unsteady risk, the calculated values of the FTA provided a suitable range underordinary conditions. No conditions changed this significantly at each life step.

8.1.9 Physical hazard Evaluation of Generated Chemical Substance
Above, we described the fire hazard from the ignition combustion of a mildly flammable refrigerant. However, even nonflammable
refrigerants such as conventional R410A and R22 can come in contact with burning appliances or high-temperature surfaces andgenerate harmful chemical substances.
According to Imamura et al. (2012), the exposure of refrigerant from a wall-mounted air conditioner to the heating apparatus of areflective-type oil stove or kerosene fan heater by contact with a heating apparatus can cause an HF concentration exceeding the 3
ppm level permitted for workers.
There were no differences among R1234yf, R32, or R410A (the present refrigerant).
However, the following conditions are required to create a situation that is harmful to people regardless of the kind of refrigerant thatreacts to generate HF.

89

(1) HF should be generated.
(2) HF should reach inhabited areas.
(3) Evasive action is not taken despite the presence of HF.
HF can appear at dangerous concentrations that are tens of times greater than the 3 ppm.
Interviews by the mini-split risk assessment SWG indicated that an old air conditioner can smell foul. However, although the use of
R410A and R22 in contact with burning appliances or high-temperature surfaces can generate harmful HF and phosgene and produce
a foul odor, this does not lead to a serious hazard severity (III); the combustion products have not caused serious illness or hospitaltreatment for more than 20 years.
Generally speaking, small children and bedridden elderly people cannot take action to avoid exposure to HF. However, because there
are very few situations in which such individuals live independently in areas where an air conditioner and heating appliance are usedconcurrently, it is unknown whether such a situation will lead to a serious hazard severity (III).
Even if the rapid burning of R1234yf and R32 by heating apparatus does not occur, the use of mildly flammable refrigerants may
produce this phenomenon and create a physical hazard through the generation of HF and other chemical substances same asconventional refrigerant like R410A. We should be alert the warning in the same way as R410A.

8.1.10 Progress in Store Package Air Conditioner (Mini-Split Risk Assessment SWG (II))
8.1.10.1 Features of Store Package Air Conditioner
Store package air conditioners have a large amount of refrigerant compared to residential air conditioners and are installed in slightly
wider spaces such as schools, offices, and small- and medium-sized stores. In the risk assessment of store package air conditioners, therefrigerant is considered to be combustible; the basic techniques used by the mini-split risk assessment SWG for residential air
conditioners otherwise usage and installation conditions used by multi-unit air conditioners applied to the evaluation of store package
air conditioners. Table 8.1.8 summarizes the main features of residential, store package, and VRV air conditioners. Figure 8.1.6
presents the risk assessment schedule for a store package air conditioner.

Product

Table 8.1.8 Comparison of features of different air conditioners
Store package air
Residential air conditioner
conditioner

Horsepower(Outdoor standard)
Cooling capacity
Refrigerant charge
Installation(Outdoor:indoor)

VRV

0.8–3 HP

1.5–10 HP

5–60 HP

2.2–8.0kW
1–2kg
1:1

3.6–25kW
2–10kg
1:1–4

14.0–168kW
5–50kg
1–3:1–64

Type of indoor unit

Wall-mount
Floor-standing
Ceiling-cassetteWall-mount
Floor-standing
Ceiling-cassette
Ceiling-suspended
Built-in duct

Type of outdoor unit

Air-coolingAir-cooling
Ice-storage

Indoor unit install location

Residence

Outdoor unit install location

GroundVerandaOfficeKitchen/Dining room
Factory
Karaoke room (Tightness)
GroundEach floor
Semi-underground
Narrow space

90

Wall-mount
Floor-standing
Ceiling-cassette
Ceiling-suspended
Built-in duct
Air-cooling
Ice-storage
Water-cooling
OfficeKitchen/Dining room
Factory
Karaoke room (Tightness)
GroundEach floor
Narrow space
Machine room

Storage

Semi-fire protect warehouse
Narrow warehouse

Logistics

Truck
Mini-van2013 fiscal year
49
Identify issues

Semi-fire protect
warehouse
Narrow warehouse
Truck
Mini-vanSemi-fire protect warehouse
Truck

2014 fiscal year
10 3

49
◆

First RA2015 fiscal year
10 3

49

10 3

Report◆Second RA

ReportThird RA
Proposal of safety measures◆

Manual or guideline

Fig 8.1.6 Risk assessment schedule of store package air conditioner

8.1.10.2 Risk assessment of Store Package Air Conditioner
Similar to the risk assessments performed for the VRV air conditioning and mini-split air conditioning, the risk of store package air
conditioners were assessed as follows.
(1) Assumption of acceptable risk
For the 7.8 million units of store package air conditioners on the market, the allowable level of risk was a serious accident once every
100 years. In practice, the hazard of an ignition accident should be assessed, but this has not yet been completed. Thus, all accidents
were treated as serious. In each stage of the life cycle excluding usage, workers handle the equipment. The workers are trained tocontrol the risk and reduce the severity even in the event of an accident. Thus the allowable ignition probability was increased by anorder of magnitude for these stages.
•Usage stage: 1.3 × 10-9
•Excluding usage stage: 1.3 × 10-8(2) Assumption of refrigerant leakage probability
Since the design specifications of a store package air conditioner were found to be similar to those of a multi-unit building air
conditioner, the refrigerant leakage probability based JARAIA questionnaire was set as follows:• Indoor unit: 1.50 × 10-5 for rapid leakage; 1.03 × 10-3 for slow leakage•Outdoor unit: 1.48 × 10-3 for rapid leakage; slow leakage was not considered because it does not produce a flammable region.
(3) Assumption of volume-time
In the model case for each life cycle stage, the amount of refrigerant leakage, installation volume, and airflow conditions wereused to calculate the flammable volume-time.
(4) Probability of presence of ignition source
Ignition sources of mildly flammable refrigerants during each life cycle stage can include the open flame of combustion equipment,a brazing burner, and open flame from smoking, fire appliances, and electric sparks; the probability of the presence of these ignition
sources was calculated.
In the FTA, we calculated the probability of the above points (2)–(4) to occur. For the risk
assessment, the ignition accident probability needed to be calculated to determine if it satisfied the limit of point (1).

8.1.10.3 First Risk Assessment Results for Store Package Air Conditioner and Future Challenges
In the first risk assessment of store package air conditioners, the ignition probabilities of the modelcases in Table 8.1.9 were calculated for each life stage.
The installation conditions for indoor use were the same as the first risk assessment of multi-unit building air conditioners. The

91

four-way ceiling cassette-type 7.1 kW air conditioner (refrigerant amount: 3 kg) is installed in general offices (floor area: 42 m2,
height: 2.7 m). Table 8.1.9 presents the risk assessment results.
Table 8.1.9 First risk assessment results of store package air conditioner
Risk: Ignition probability
Model
R32
Logistics
Semi-fireproof warehouse
1.6 × 10-12
Installation
3.6–14.0kW
2.3 × 10-9
R32: maximum charge of 4 kg
Use (Indoor)
5.0 × 10-11
Indoor: Office ceiling cassette(Outdoor)
6.7 × 10-10
Outdoor: On the ground
Service
3.0 × 10-9
disposal
2.5 × 10-9
As shown in the table, the first risk assessment found that the ignition probabilities met the allowable value in all life stages. Thismodel case considered common usage conditions and is believed to be applicable to a large percentage of the market. We thenperformed a second risk assessment for cases where the expected risk is large but the probability of occurrence is low. Table 8.1.10
summarizes the model cases.

Step

First

System(Refrigerant
charge)No additionalchargeMaximum: 4 kg

Table 8.1.10 Each step of risk assessment for store package air conditioners
Indoor unit
Indoor place
Outdoor Place
Storage

SecondAdditional charge
Maximum:8kg

Third

25kW, Ice
thermal storage
Maximum:19 kg

Transport

Ceiling cassette

OfficeGroundMiddle warehouse

Truck•Ceiling cassette•Floor standing•Office•Kitchen•Tight space•Ground•Each floor•Semi-underground•Narrow space•Truck•Small warehouse•Truck•Minivan

↑

↑

↑

↑

↑

A store package air conditioner can have a maximum amount of piping of 30 m for indoor and outdoor units without requiring
additional refrigerant charge. We added local filling depending on the pipe length, which increased the amount of refrigerant held inthe system as well as the risk of refrigerant leakage. Refrigerant that leaks from floor-standing type air conditioners tends to stay on thefloor, so a flammable volume is easily generated.
Commercial

kitchens,

which

have

many

ignitionsources,andclosedkaraoke

rooms

with

littlenaturalventilation required attention. Sometimes, the outdoor units of store package air conditioners are installed in narrow spaces. Storepackage air conditioners can be placed in relatively small spaces like a station wagon during transportation and small warehouses by aretailer. As noted above, the second risk assessment evaluated cases where the risk of ignition probability was expected to be higher. A
risk assessment was also performed for 25kW ice thermal storage systems with refrigerant amounts in excess of 8 kg to consider
the most severe cases. We plan to continue to develop safety measures as necessary.

8.1.11 Conclusion and Future Subject
The mini-split risk assessment SWG studied wall-mounted type mini-split air conditioners using R1234yf and R32. No issues withthe refrigerants were confirmed by the results. For R1234yf, the flammable concentration varies with the humidity. The objective of
the risk assessment was to determine if the mildly flammable refrigerant R410A can be applied to conventional mini-split air

92

conditioners using R32 without significant design changes. In order to match the conventional efficiency and performance from using
R1234yf, the heat exchanger needed to be increased approximately 1.4 times in size, and a large compressor needed to be developed
to ensure long-term reliability.
A risk assessment was also performed on floor-standing type air conditioners using R32. The results confirmed that this refrigerant
can be used in limited installation space. The risk assessment for multi-unit residential air conditioners with multiple indoor
units to one outdoor unit found that the relationship between the installation space and amount of refrigerant charge is one of the mostimportant issues. Consistency with international standards on this matter is another issue and will continue to be the subject of further
study by another working group of the Japan Refrigeration and Air Conditioning Industry Association.
A risk assessment was performed for one-to-one store air conditioners using R32. The primary risk assessment found thatceiling installations of store air conditioners were below the risk tolerance for ignition in all life cycle stages. Based on the
results, safety measures are unnecessary.
To reduce the risk, the SWG revised the manual for service and installation. Similar to the manual issued by the Japan Refrigeration
and Air Conditioning Industry Association, the SWG proposed countermeasures for R32 in particular.
The Tokyo University of Science (Suwa), University of Tokyo, and National Institute of Advanced Industrial Science andTechnology participated in the mildly flammable refrigerant risk assessment study group to improve the accuracy of the FTA results.
We also revealed the extent of the hazard severity. We describe the developments above to promote the risk
assessment of mini-split air conditioners with higher accuracy.

Acknowledgments
Shigeharu Taira, Takeshi Watanabe, and Kenji Takaichi summarized the surveillance study for the JRAIA mini-split air conditioner
risk assessment SWGs I and II. We thank the 11 committee members: Mr. Madoka Ueno of Sharp Co.; Mr. Tsuyoshi Yamada of
Daikin Co.; Mr. Koichi Yamaguchi and Mr. Yasuhiro Suzuki of Toshiba Carrier Co.; Mr. Ryoichi Takafuji and Mr. Kazuhiro Dobashi
of Hitachi Appliance Co.; Mr. Toshiyuki Fuji of Fujitsu General Co.; Mr. Tetsuji Fujino of Mitsubishi Heavy Industry; and Mr. Takao
Hirahara, Mr. Hiroaki Makino, and Mr. Yasuomi Suzuki of Mitsubishi Electric Co.
We also thank Manager Matsuda and Section Chief Hasegawa of JRAIA for their secretarial work.

References•Risk Assessment of Propane Room Air-conditioner, The International Symposium on New Refrigerants and Environmental
Technology, Yao et al. (2000.9)•Practical Business Method for Risk Assessment Handbook, MITI, (2011.6)•Risk Assessment of HFC-32 and HFC-32/134a (30/7 wt%) in Split System Residential Heat Pumps: DOE/CE/23810-92•Study on Minimum Ignition Energy of Mildly Flammable Refrigerant, Kenji Takizawa, AIST (2011)•Flammability Characteristics of HFO-1234yf, Minor, AIChE Process Safety Progress (Vol. 29, No. 2)•Determining Minimum Ignition Energies and Quenching Distances of Difficult to Ignite Components, Dean Smith, Journal of
Testing and Evaluation, Vol. 31, No. 3•Research on the Ascending Current of the Pan Installed in the Residential Gas Range, Honda, Osaka University Graduation paper•Evaluation of Fire Hazards of A2L Class Refrigerant, The International Symposium on New Refrigerants and Environmental
Technology, Imamura et al. (2012.11)•Next Generation Low GWP Refrigerant HFO-1234yf Part 2, Minor et al., ASHRAE meeting N.Y. Jan (2008)•Compact Handbook of Static Electricity, Static Electricity Society•Evaluation of Refrigerant Leakage, The International Symposium on New Refrigerants and Environmental Technology, Hattori et al.

93

(2012.11)•Physical Hazard Evaluation for using Air-Conditioning Systems Having Low-Flammable Refrigerants with the Fossil-fuel Heating
System at the Same Time, Academic Journal Reito of JSRAE, Vol. 29 No. 4, pp. 401-411, Imamura et al. (2012)•Progress Report of 2011, Japan Society of Refrigerating and Air Conditioning Engineers.
•Progress Report of 2012, Japan Society of Refrigerating and Air Conditioning Engineers.

948.2 Progress of SWG for VRF System Risk Assessment
8.2.1 Introduction
The risk assessment of VRF systems using mildly flammable low-GWP refrigerants was divided into first and second
assessments. Fig. 8.2.1.1 shows an outline of the schedule. A risk assessment was conducted for each life stage, as
shown in Fig. 8.2.1.2. In the first risk assessment, we examined the basic data and methodology necessary for fault tree
analysis (FTA), including an estimate of the probabilityof refrigerant leaks occurring in the market, evaluationof the various causes of ignition, and examination of
the calculation method to determine the probability offire. Furthermore, we created fire accident scenarios
and an FTA for typical installation cases in the market
and estimated the probability of a fire accident
occurrence. The second risk assessment examined
installation cases considered rare in the market but
possessing high risk, and safety measures were
proposed to reduce such risks. The GL-13 1 safety
guidelines for the safe use of mildly flammable
refrigerants in VRF systems are slated for enactment in
the autumn of fiscal 2014.

8.2.2 Issues for VRF Systems Using Mildly Flammable
Table 8.2.2.1 presents the features of VRF systems. The most distinctive feature is the large amount of refrigerant
charge in the refrigerant circuit that can be completely discharged from one indoor unit in the case of an indoor
refrigerant leak. As there are many connections in the refrigerant piping, rigorous refrigerant leak checks are conductedin a two-layer check system after the piping is installed:
once in the form of a tightness leak test at positive
pressure and once to check for vacuum leaks at
negative pressure. Additionally, specialist techniciansand highly skilled service providers normally conduct
mounting installation, repairs, and maintenance; thislowers the occurrence of operational errors.
Mildly flammable A2L refrigerants feature anespecially high lower flammable limit (LFL) andminimum ignition energy (MIE) compared with otherflammable refrigerants. The LFL is high, and it takes alarge amount of refrigerant to generate flammablespace. Moreover, even ignition sources that can ignite
highly flammable propane gas cannot ignite an A2L
refrigerant with a large MIE.
When calculating the probability of fire, ascertaining
how flammable space occurs at the time of refrigerant
leaks and which ignition sources are present that arecapable of igniting refrigerant is necessary.

8.2.3 Identification of Risks
The second risk assessment investigated the likelihood of refrigerant accumulation according to the indoor unit1

GL-13: Guideline of design construction for ensuring safety against refrigerant leakage from multi-split system air
conditioners, published by The Japan Refrigeration and Air Conditioning Industry Association95

configuration and installation site, the ignition source type according to the type of business installation, and ventilation
conditions. Installation cases thought to have high risks were selected. Among indoor units, cases were selected for
instances where floor-standing units were installed in restaurants having small rooms prone to refrigerant accumulationand open flames and for instances where ceiling cassette air conditioners were installed in karaoke shops that eliminatedgaps under doors to prevent sound leakage, which would severely limit natural ventilation. Ceiling spaces are also
usually assumed to have limited ventilation capabilities. Risks were extracted for outdoor units in areas prone torefrigerant accumulation as well as for units installed on each floor, semi-underground, or in machinery rooms. The
risks when a slightly flammable refrigerant is improperly charged to an existing R410A unit were also investigated.

8.2.4 Preparations for Risk Assessment
8.2.4.1 Setting allowable levels
The probability of fire from an allowable risk is typically different depending on the degree of severity; however, as theassessment of the degree of danger was incomplete, we set allowable levels under the assumption that all fire accidents
are serious and fatal. As there are approximately 10 million indoor units in use in the VRF system market, if theallowable level of a serious accident occurring were once every 100 years, the allowable level for time of use (indoors)
would be 10-9 or less. The number of units was increased four times for time of use (outdoors), and we multiplied 10-9
by 4. Apart from the time of system operation, the people who normally handle equipment are service providers, notconsumers, and it is likely that the degree of danger can be reduced through self-protection even if an accident occurs.
Therefore, the allowable probability of an accident was increased by one order of magnitude and assumed to be 10-8 orless. This point incorporates the approach of Professor Mukaidono of Meiji University.

8.2.4.2 Probability of number of leaks occurring for different refrigerant leak velocities
The international standard (ISO 5149 Part 1 Ch A5) on the amount of refrigerant charge for VRF systems has adopted
an indoor refrigerant leak velocity of 10 kg/h under the condition of no vibration from compressors. To understand theactual conditions, we recovered parts that caused refrigerant leaks in the market and determined the bore diameters byusing a leak velocity test conducted with nitrogen. The refrigerant leak velocity was obtained from the bore diameters
and refrigerant pressure.
Fig. 8.2.4.1 shows the results of the 22 indoor unit
parts with leaks that were recovered from the market. The
bars with arrows above them indicate emergency calls byservice providers based on reports from customers ofwhite smoke coming out of the indoor units. Of the four
instances, the leak velocity of the liquid was relatively
high for three of them (1–10 kg/h). The leak velocity was
0.01 kg or less in only one case. This one case wasassumed to have no high-speed refrigerant leak; thecustomer reported the incident after seeing steam
produced during operation after the equipment had runout of gas. As the other cases with white smoke indicated96

a refrigerant leak velocity of close to 10 kg/h, we can infer that, if a high-speed leak occurs, in many cases the customer
would see white smoke and realize that there was an abnormality.

Using a similar method, we also measured 26 leaksamples from outdoor units. Fig. 8.2.4.2 shows theresults. Compared with the indoor units, the outdoor
units had higher leak velocities; in three cases, theleak velocity exceeded 10 kg/h. Based on the above
results of the samples, finding the probability of thenumber of leaks at different velocities at the scale ofparts per million (ppm) was difficult. Therefore, forall cases of leaks handled by service providers overthe period of 1 year, we extracted the number of casesof customers reporting white smoke or an abnormal
smell as well as the number of cases where service
providers diagnosed leaks as originating from abroken pipe or hole in the heat exchanger or pipe. To
calculate the number of high-speed leaks, we
multiplied this number by 10 for indoor units and by
100 for outdoor units. Since there were no burst leaks
with indoor units of VRF systems, we calculated thenumber of burst leaks to be zero. We judged that theremaining leaks were slow leaks of 1 kg/h or less. For
outdoor units, as there were samples of leaks
exceeding 10 kg/h, we calculated 1/10 of thehigh-speed leak cases to be burst leaks. Table 8.2.4.1
presents the results.

8.2.4.3 Assessment of ignition sources
Table 8.2.4.2 presents the assessment of each type of
ignition source. Although sparks from electrical partsand smoking devices are major ignition sources forhighly flammable gases such as propone, they do not
become ignition sources for mildly flammable refrigerants, which have a high MIE value.

8.2.4.4 Probability of human error
Refrigerant leaks during work stages, which include installation, repair, and disposal, occur as a result of human error,
such as incorrect valve operation by the service technician. Table 8.2.4.3 presents the error rates corresponding toworker conditions according to Hashimoto. The range between 10-2 and 10-5 is set for normal, relaxed conditions;however, as service providers handling VRF systems are highly trained, we selected 10-4 within the FTA to represent theprobability of human error.

97

8.2.4.5 Calculation method for probability of fire
A fire occurs when a refrigerant leak causes theformation of a flammable space and an ignition sourcethat can ignite the A2L refrigerant encounters theflammable space in both space and time. Here, fire isdefined as all ignition events if the flammable spaceof a refrigerant happens to contact ignition
sources, regardless of the order of magnitude of
the ignition. Table 8.2.4.4 presents this probability
calculation.
The fire trigger is the operation of the ignition source(e.g., electric spark). In the case of flammable gas
coming into contact with a burning candle and igniting,the trigger is the formation of a flammable space. If theformation of a flammable space happens first in time,
the trigger is the operation of the ignition source; if thecause of ignition first exists in a continuous state, thetrigger is the flammable gas. The probability of fireoccurring from one ignition source is the sum of these
two triggers. In order to calculate the risk of each life
stage, the probability of fire is calculated after
determining which trigger is dominant.

8.2.4.6 Method to predict accident probability
from improper charge
In order to determine whether the service port specifications for equipment using a mildly flammable refrigerant
should be changed from the specifications of conventional refrigerant equipment, we calculated the probability of anignition accident occurring from R32 refrigerant being improperly charged to R410A equipment when the specifications
are the same. Fig. 8.2.4.3 presents the calculation method.

8.2.4.7 Setting of indoor model(1) Small conference room of office
The 56 kW model (20 hp) was selected to represent the outdoor unit capacity based on the survey results for thecapacity distribution of a number of units shipped for office rooms. For the indoor unit capacity, the 7.1 kW model (2.8hp) was selected in a configuration of eight indoor units connected per outdoor unit. Here, the air conditioning load wasassumed to be 170 W/m2 for the floor area. This is expressed in Fig. 8.2.4.4. The risk assessment was performed bytargeting office room 1 (6.5 m × 6.5 m), which was assumed to be the size of a small conference room in an office.
Ventilation was provided by one air inlet and one air outlet
in the ceiling and one gap under the door (undercut part).
The ventilation flow from the air inlet and air outlet was
169 m3/h based on the registered number of people
according to Article 28 of the Building Standard Act.
Because the wind velocity was established to be 2.0 m/s as
specified by the Public Buildings Association, the air inlet
and air outlet were given dimensions of 0.2 m × 0.2 m. For

98

Table 8.2.4.7 Conditions and results of CFD simulations for office 1
No.
1
2
2'
4
5
6
8
9'

Refrigerant

ChargeAmountM [kg]
26.3
88.1

R32
26.3

Leak
Velocity[kg/h]
10
10
10
1
10
10

Ventilation
Amount[m 3/h]
0
0
0
0
169

Undercut

Vent

Condition

N
Y
Y
Y
Y
Y
N
Y

Open
Open
Closed
Open
Open
Open
Open
Open

Most severe condition. Widest flammable space
Natural Ventilation through undercut
Natural Ventilation through undercut, Vent closed
Natural Ventilation through undercut
Mechanical ventilation, ACH=1.5 [/h]Vent. starts after leak detection
Shut-off valve operates after leak detection
Effect of refrigerant in No.2

0 to 169*1)
0
10 to 1*1)
R1234yf
29.4
100*1) Operation after activation of leak detector*2) Charge amount of R32, M = 29.4 [kg] in case of R1234yf

Space-Time Product ofFlammable region
M = 26.3*2) M = 88.1
1.70*100
3.66*104-1
8.30*102.80*100
1.62*100
0.00*100
7.00*10-1
7.30*10-1
3.10*10-2
6.30*10-1

the door configuration, the width was 1500 mm, and the dimensions of the door undercut was set to 10 mm. The
amount of R410A was set as the standard refrigerant amount, and the calculation was performed by multiplying thisvalue by a coefficient of 0.85 for R32 and 0.95 for R1234yf. Although
the refrigerant amount (Table 8.2.4.5) was determined under the assumption of a typical installation, the case of the
maximum refrigerant amount was also evaluated (Table 8.2.4.6).
Table 8.2.4.7 presents the simulation conditions and results for office room 1. Here, the slow and fast leak velocities
for the refrigerant were 1 and 10 kg/h, respectively. Tokyo University and JRAIA collaborated on this research.
The average possible volume of flammable space decreased with operation of mechanical ventilation equipment(model no. 6) and an isolation valve that was installed for the refrigerant piping (model no. 8); the safety measures werealso effective.
When natural ventilation was available from the door undercut, no flammable space was generated throughout theentire space (model no. 4) based on the refrigerant concentration
distribution, expressed in Fig. 8.2.4.5, for the refrigerant leak velocity E= 1 kg/h. Fig. 8.2.4.6 presents the velocity distribution. The R32
concentration in space was not increased by the air flow fromthe air inlet and outlet in the ceiling. To lower the volume, themechanical ventilation opening must be open, and an undercut
must be established underneath the door. Namely, theexistence of an air inflow and outflow is a necessary condition.
Incidentally, the results of a simple simulation where theconcentration changes with the location were consistent withthe refrigerant concentration by the ceiling installation type(Fig. 8.2.4.7). Thus, we decided to execute a simple simulation
using models where the ventilation flow is regulated by theceiling installation type.
(2) Small Rooms of Restaurants
Fig. 8.2.4.8 shows the models. Floor models were installed in
the individual rooms of Japanese-style restaurants. The
refrigerant amounts were set to 52.8 kg for R32 and 58.5 kg
for R1234yf. Table 8.2.4.8 presents the analysis conditions and results.
For the case without measures, ventilation openings for the air inlets andoutlets were established in the ceiling, and the ventilation flow was set to
112 m3/h. When a gas cooking stove is being operated (calorie control
amount of 3

99

Table. 8.2.4.8

Conditions and Results of CFD simulations for floor-standing unit in Japanese restraurant
Flammable Region

Analysis Condition

Leak
Rate

Refrigerant

Charge[kg]

Without
Measures

R32

52.8

10

With
Measures

R32

52.8

10

[kg/h]

Mixing in
Unit

Ventilation
AmountVentilation Condition

3[m /h]

Inlet

Outlet

No
Yes

112

Ceiling

Ceiling

Yes

164

Ceiling

300mm above floor level
200mm above floor level
30mm above floor level

Mean
Volume

Time

3

[min]

1.17
1.28
0.01
0.10
1.30

910
900
320
317
317

[m ]

Space-Time
Product[m 3 min]

1070
1150
416
30.7
2.40

kW), a ventilation flow of 500 m3/h is necessary to maintain an indoor CO 2 concentration of 1000 ppm; however, thethreshold value was set to 1/5 of this value to ensure safety. When leaks occurred in the floor models, the refrigerant
remained in the vicinity of the floor. However, when there was mechanical ventilation with air inlets and outlets
installed in the ceiling, the flammable space became large without enabling dilution of the refrigerant. For cases where
the measures are determined by GL-13, it is necessary to construct air outlets that are in the vicinity of the floor. The
ventilation flow was set to 164 m3/h (= 10/0.061) to ensure that the concentration would not exceed RCL0.061 kg/m3 at
a leak velocity of 10 kg/h. The results showed that changing the height (underside) of air outlets to 30–300 mm had asignificant impact on the flammable space volume.
(3) Karaoke
Fig. 8.2.4.9 presents the models. We referred to an actual survey
for the Nomura and Kitajima karaoke boxes. In order to prevent
sound leakage, a ventilation system was employed without naturalventilation. The maximum refrigerant amount was set to 88.1 kg,
the volume of the karaoke box was set to 9.5 m3, and customers
changed once every 3 h. However, once the refrigerant
concentration lowered after the customers changed, we made theentire room a flammable space for a short time. We assumed
candles, combustion-type heaters, gas stoves, and electricalequipment, as shown in the figure, beginning with the karaokeequipment. The concentration was determined by the simplified
simulation.
(4) Ceiling Space
The compartment for the ceiling space of office room 1 inFig. 8.2.4.10 was completely separated from the other spaces,
and we hypothesized a worst-case scenario at the time ofsystem operation in the FTA: the entire area becoming a
flammable region after a refrigerant leak and having this lastfor ten years. As the ignition source, we considered theignition of an indoor unit and short-circuit accidents. For
servicing, we set the flammable region as continuing for 4 h;
this was shorter than in the case of system operation because
dilution can be expected through opening for inspection. The
volume was determined by assuming a ceiling space forroom 2.

8.2.4.8 Setting of Outdoor Model
We selected an upper air outlet, three-sided-heat exchange
type model with 56 kW (28 kW × 2 units), which is the mostcommon among market installations. Fig. 8.2.4.11 presents theinstallation patterns. We assumed four installation patterns: atypical installation pattern with no obstructions in the vicinity,
the installation pattern of each floor, the installation pattern in amachinery room, and the installation pattern of thesemi-underground. The refrigerant amount was set as 85% (26.3kg) of the regulation amount of R410A, and the conditions wereset as a uniform leak from one heat exchanger in a connected
installation.
Figs. 8.2.4.12–14 show the outdoor unit models. The

100

Table 8.2.4.9 Conditions and results of CFD simulations for outdoor models
Case
Usual
Each floor
Usual
Each floor
Semi-underground
Usual
Each floor
Usual
Each floor
Semi-underground

Condition
Leak rate Air velocity Leak time Mean volume[kg/h]
[m/s]
[min]
[m3]
0.0E+00
10158
1.0E-0608.3E-0275
21
1.9E-01
1.6E+01
0.0E+00
10158
0.0E+00
9.4E-030.5
1.8E-0175
21
3.1E+00

Results
Space-Time Product
Time
[min]
[m3×min]
0.0E+00
0
4.3E-064
1.8E+0021
4.0E+00
21
6.3E+043852
0.0E+000
0.0E+000
2.0E-0121
3.8E+00
22280
8.8E+02

machinery room had dimensions of 6.6 m × 3.3 m × 5 m (height) and was equipped with a mechanical ventilation
device.
Table 8.2.4.9 presents the conditions and results for a concentration distribution analysis of the outdoor models.
shows the results for a concentration distribution analysis of semi-underground installations. The
Fig. 8.2.4.15
leak velocity was set to 75 kg/h. For the 20-min period until the leak was complete, a flammable region layer rose fromthe floor space, where the top concentration was LFL and the bottom concentration was URL. When the leak wascomplete, the thickness of the flammable region layer increased by diffusion.
For the installation patterns other than the semi-underground installations, the flammable region dissipated in tens ofseconds after a refrigeration leak. In the case of semi-underground installations, refrigerant accumulated in the
flammable region, which did not dissipate for 64 h. Fig. 8.2.4.16 indicates the time transition for the flammable regionsof semi-underground installations.

8.2.5 Results of Risk Assessment and Safety Measures
In the first risk assessment (progress report presented in fiscal 2012), we created an FTA by following the risk

101

assessment of the R290 mini split. Here, because the ignition source evaluation and concentration analysis of the mildly
flammable refrigerants were incomplete and the actual conditions in each work stage were not fully identified, theresults overestimated the accident probability for each stage. These overestimations were caused by factors such as
employing accident scenarios that estimated flammable spaces as being larger than in actual cases, including cigarette
lighters, electrical outlets, and light switches as ignition sources, and by employing accident scenarios that estimated aburst leak after refrigerant recovery and ignition by a brazing burner. In the second assessment, we considered theignition evaluation results of the Tokyo University of Science, Suwa, and the National Institute of Advanced Industrial
Science and Technology, the concentration analysis results of Tokyo University and each company, and the workplacesurveys to create an FTA that better reflected the actual conditions. The risk assessment results for each life stage arepresented below.

8.2.5.1 During transportation storage (manufactured product)
Transportation storage was divided into warehouse storage and transportation, and various risk investigations were
performed.
For the investigation, 1000 units were stored in a medium-sized warehouse with an area of less than 1000 m2 and astandard fireproofing structure following the Building Standards Act. The value of space-time product is 8.4*10-3[m3min] for storage. Cigarette lighters owned by workers and spark ignition at the time of freight handling of theforklift were assumed to be ignition sources, and the frequency of refrigerant leaks was set to be the same as during use.
The storage frequency of air conditioners was set to 1/15 based on a service life of 15 years, and an FTA was created.
This resulted in an ignition probability of 7.8 × 10-17–1.2 × 10-16 (ignition/unit for 1 year), which is below the allowanceof 10-9.
However, ignition sources are not believed to exist inside freight rooms, so there is no ignition combustion even if therefrigerant leaks. Because the leaked refrigerant simply diffuses from freight rooms, in which open fires are prohibited,at the time of loading and unloading, and there are no flammable regions, the necessity for an FTA investigation isextremely low. Thus, we determined that there is no risk at the time of transportation storage.

8.2.5.2 During installation
The risk assessment was performed as follows.
(a) The risk of brazing work for connecting pipes was estimated in detail. Usually, connection pipes are brazed
when the pipe is not connected to the outdoor unit; consequently, there is little possibility that refrigerant will leak
during brazing. However, because the possibility is not zero, we assumed that piping connections were brazed under
actual conditions where the risk of outdoor units was 10% and calculated the fire probability for the ignition source (gasburner) based on the following assumptions.
(b) Using the survey analysis results for electric shock/secondary accidents, we calculated the probability for thepresence of electrical sparks in a ceiling space.
(c) We considered the following causes of refrigerant leaks for outdoor units: (1) a faulty valve, (2) a charging mistakeof R32 at the N2 permutation, (3) the reuse of existing piping, and (4) connecting a pipe to the outdoor unit prior topiping work. We assumed the following ignition sources for outdoor units: (5) preloading unconnected outdoor units inthe work vicinity of brazing and (6) boilers.
We created an FTA that reflected the above factors and found the fire probability to be 94% for outdoor units intypical installations with no obstacles around them and 99% for indoor units with ceiling installations. The results were
1.9 × 10-9, which is within the allowable level of fire probability.
For semi-underground outdoor units and machinery room installation cases, we exceeded our target values. For
indoor units, all were within the allowable level. The major causes of ignition sources were brazing work for connection
piping (prior to charging the refrigerant) and a boiler. Because the values were an order of magnitude higher than thetarget values for accident rates of these cases, we decided that carrying refrigerant leak detection devices during theperforming of brazing work would be an effective countermeasure. As a result, all conditions fell to within theallowable level.

8.2.5.3 During system operation (indoors)
We investigated examples of typical installations and worst-case scenarios. For typical installations, we assumed
offices (office 1: small rooms) and decided to investigate cases in which mechanical ventilation was implemented(model no. 5). First, in worst-case scenarios, we simply calculated the ignition probabilities for 28 types of building
uses that differed in terms of the presence of ventilation, type of ignition source, and room size. Based on the results, weselected two installation cases where the fire probability was pre-estimated to be high for further investigation. The firstcase comprised a ceiling installation type with the possibility of open flame as ignition sources, a small room size, and alack of door undercuts (e.g., karaoke rooms). The second case comprised a floor standing type with the possibility ofopen flame as an ignition source (e.g., small restaurant rooms for customers). We also decided to investigate the ceiling102space for office 1.
We assumed usage rates for equipment that accompany an open flame and calculated the ignition probability for thenumber of operation times of the ignition source and calculated the probability for other equipment (primarily electrical
products) from NITE accident information on ignition probability rates.
In the results, we were not able to satisfy the allowable safety level of under 10-9 that was set in this risk assessment for
the two worst-case scenarios. Thus, safety measures are necessary, and we confirmed that an allowable safety level ofunder 10-9 can be set by operating ventilation after detection of the refrigerant leak by equipment.

8.2.5.4 During system operation (outdoors)

Table 8.2.5.1 Number of operation times of ignition sources

For outdoor unit equipment, we established theper volume and minute [times/(m3×min)]four patterns shown in Fig. 8.2.4.11. We selectedElectric spark
Smoking tool
Boilerfrom its fire accident
three items as ignition sources: smoking (match,
Usual
7.97E-08
9.43E-15
1.78E-08
lighter), electrical sparks of the outdoor unit, and a
Each
floor
2.82E-06
6.68E-13
2.87E-06
boiler. We calculated the fire probability from the
Machinary room
1.87E-06
8.83E-14
space-time product value (estimated for machinery
Semi-underground
1.03E-06
1.79E-13
6.69E-05
rooms from the space-time value calculated forsemi-underground) based on the concentration analysis results and the number of times that the ignition source isoperated; these are presented in Table 8.2.5.1. Those numbers were calculated based on the following: a smoking rate of
33.6% for Japanese men, at an average of 16 cigarettes a day (JT statistics); occurrence of 5.6 accidents every year on
account of smoke and ignition from electric sparks (NITE statistics); and 0.1% market penetration rate of boilers.
An FTA was created based on the above preconditions, and the fire probability for each pattern was calculated. It isshown that a fire probability is less than the criterion of 4.0 × 10-9 for typical and each floor installations ; consequently,
safety measures were unnecessary. The refrigerant diffusion velocity for leaks in semi-underground was extremely slow,
the ignition probability was 1.1 × 10-7, and the allowance level was not satisfactory. Incidentally, ventilation equipment
is present in machinery rooms. Furthermore, because the boiler intake and exhaust also control the specialized duct,safety measures based on fixed conditions are unnecessary as refrigerant leaks do not come in contact with the burner.
For machinery room installations and semi-underground equipment, the fire probability changes according to theamount and spatial volume of the refrigerant or the height of the semi-underground. The maximum refrigerant amountneeds to be regulated to correspond to standards that determine the necessity of safety measures and spatial volume forthe installation of outdoor units and the amount of necessary ventilation. An investigation of the constraining conditions
is planned for the future.

8.2.5.5 During repair
Having a burner for the primary ignition source significantly affects the fire probability within the FTA, andrefrigerant leakage accompanying burner operation is one of the main factors for the formation of flammable regions. In
the second risk assessment, the probability of fire accidents was within 10-8 for indoor ceiling installation, outdoor
aboveground installation, outdoor installation to each floor, and ceiling space. However, because the values were
exceeded for indoor floor-standing installation, outdoor semi-underground, and machinery room installation, safetymeasures were necessary. For indoor floor-standing installations, countermeasures include natural ventilation(according to ISO5149), installing the lower part of the door position 30 mm from the floor surface, training service
providers (e.g., when a refrigerant leak is noticed during burner work, immediately extinguish the burner), and having
workers carry refrigerant leak detection devices to check for refrigerant leaks during work. For outdoor installations, we
controlled risks to within the allowance values by measures including installing ventilation devices together withsemi-underground and machinery room installations, training service providers in the same way as for indoor
installations (e.g., when a refrigerant leak is noticed during burner work, immediately extinguish the burner), andhaving workers carry refrigerant leak detection devices.

8.2.5.6 During disposal
We examined the risks during work to dismantle the units and pipes at an installation site. Ignition sources wereassumed to be burners, electrical short-circuits accompanying wiring work, and smoking tools.
Regarding fire ignition scenarios from burners, we considered situations where fires are ignited from refrigerantleaking from units for replacement by burners being used in the piping work of new units. In this scenario, therefrigerant leak from removed old units was assumed to happen simultaneously while the burner was being used
continuously for the working pipe of the new unit. We made the replacements comprise 50% of the total. Furthermore,
we made 10% of the units operate with the simultaneous installation of new units during replacement. Consequently,
this scenario established that 5% of the units operate during the dismantling.
In the results, the detected risks exceeded allowable values when outdoor units were installed semi-underground or in103

machinery rooms. We assumed the following measures to lower fire probability:
Measure (1) Provide risk education and warning notices for smoking and using combustion equipment, and train
workers to immediately extinguish the fire of burners during a refrigerant leak.
Measure (2) Require workers to carry a refrigerant leak detection device when working in small narrow places (e.g.,
semi-underground, machinery rooms).
Under these circumstances, we also considered the probability of forgetting to carry detection devices (10%).
For outdoor units installed semi-underground and in machinery rooms, the fire probability fell within the allowablerisk range (under 10-8) when both measures (1) and (2) were executed. Even for the other installation cases, measure (1)should be performed. For cases of replacement and simultaneous operation, measure (1) causes the fire probability tofall within the allowable risk range in all installation cases.

8.2.6 Summary of Results
Table 8.2.6.1 summarizes the results of the second risk assessment for R32. When the risk exceeded allowable levels,
we executed safety measures to decrease the risk. In ceiling installation units/offices, the risk fell below the allowablelevel through the use of mechanical ventilation. VRF systems are most often applied in offices, and ceiling installation

units make up more than 95% of theindoor units. Because the risk may behigher than the allowable values forventilation and refrigerant conditions
that differ from conditions establishedduring this assessment, appropriate
safety measures are needed thatcomplywith
ISO5149.
Infloor-standing installations/restaurants,
the risk exceeded allowable values
during the system operation andmaintenance of indoor units forceiling installation/karaoke. The risk
also exceeded allowance levels except

104during transport/storage in semi-underground installations. All risks were lower than the allowable level with regard to
improper charging in the life stages ofsystem operation, repair, and disposal.
Tables 8.2.6.2 and 8.2.6.3 present safetymeasures.
With regard to the life stage of repairs anddisposal, which is when a burner is often
used, service providers need to be trained,
and the habit of carrying refrigerant leakdetection devices during installation, repair,and disposal at sites prone to refrigerant
accumulation needs to be cultivated.
Tables 8.2.6.4 and 8.2.6.5 indicate theignition sources and refrigerant leaks thathave the largest impact on the probability ofaccidental fires in risk scenarios. Openflames such as combustion-type heaters andgas stoves are the most common ignition
sources during use, and welding burners are
the most common sources during installation,
repair, and disposal. To reduce risk,
measures concerning open flames indoors
and the handling of burners during work arenecessary. Ignition by oil lighters is mostcommon in offices, machinery rooms, andtransportation storage facilities. Tokyo
University of Science, Suwa, is currently
evaluating how oil lighters can become
ignition sources in a flammable space, andthe risk values may change according totheir results.

8.2.7 Future Development
8.2.7.1 Concerning safety measure for floor-standing units
In ceiling installation units, dilution occurs when the refrigerant mixes with the surrounding air according to theacceleration effect; the leaked refrigerant falls from the ceiling toward the floor (Fig. 8.2.4.6), and the indoor
concentration becomes a near uniform distribution. However, this dilution effect cannot be anticipated for floor-standing
units, and the floor level concentration becomes high; this makes it easy for flammable space to form.
Future investigation is necessary on safety measures for mildly flammable refrigerants, the natural ventilation effectof temperature deviation between indoors and outdoors, and the location of mechanical ventilation openings infloor-standing units to prevent suffocation accidents as per GL-13. However, GL-13 does not anticipate whether or not
refrigerant accumulation in the vicinity of the floor will be diluted by low-to-high mechanical ventilation.
In the concentration distribution analysis, the formation of flammable space greatly changes according to theconcentration boundary conditions for the leaked refrigerant emitted from the floor-standing unit. Three companies that
use the low boy-type floor-standing unit performed experiments; a comparison with the analysis results (even of the mix
inside the unit) showed that the experimental results could be reproduced. Currently, we can use this analysis method toeffectively evaluate both mechanical ventilation and natural ventilation.

8.2.7.2 Handling of R1234yf and R1234ze
Because the work from risk assessment to safety measure proposal has been completed once, priority was given to R32
as the target refrigerant. Based on these results, there is a plan to evaluate the special characteristics and issues ofR1234yf and R1234ze that differ from those of R32. Because their molecular weights are more than twice that of R32,
the evaluation is proceeding with regard to the impact on refrigerant accumulation from a refrigerant leak when the gas
density is high and whether this affects the flammable limit range spread when the air is humid.

8.2.7.3 Ideal for safety and market regulation
Because large amounts of refrigerant are used, executing necessary safety measures is important for the safe use of105

mildly flammable refrigerants in VRF air conditioning systems that have higher risk than pair-type air conditioners. The
JRAIA safety guidelines for GL-13 are to be revised in the future based on this risk assessment, which we feel should
be disseminated.
The penetration of VRF systems with a mildly flammable refrigerant into the market is impossible if excessive safetymeasures are enacted when the necessity is low, which means that they will not help reduce global warming. Conversely,
effective penetration reduces safety when safety measures are neglected for cases where the necessity is high.
Consequently, rules need to be imposed based on a risk assessment that reflects the current situation to enact safetymeasures that are logical and not excessive or insufficient. Although combustion heating devices at the time of use andbrazing burner at the time of work (Table 8.2.6.4) were found to be the primary ignition sources in this risk assessment,
ignition sources must be properly evaluated for safety measures to be effective. As a primary factor is the generation of
flammable space, engineering measures should be investigated in order to further reduce the probability of a rapid
refrigerant leak producing a flammable space.

Acknowledgments
This report was created through the joint cooperation of Yukio Kiguchi (Toshiba Carrier), Katsuyuki Tsuno(Panasonic), Hiroaki Tsuboe (Hitachi Appliances), Shuntaro Ito (Fujitsu General), Koji Yamashita (Mitsubishi Electric),
Tatsumi Kannon (Mitsubishi Heavy Industries) and Chief Investigator Ryuzaburo Yajima (Daikin Industries). In
addition, Hiroichi Yamaguchi (Toshiba Carrier), Eiji Sato (Hitachi Appliances), Takuho Hirahara (Mitsubishi Electric),
Kenji Takaichi (Panasonic), Shinya Matsuoka (Daikin Industries), and Shigeharu Taira (Daikin Industries) lent theircooperation as observers. We express our deep appreciation to Kazuhiro Hasegawa (JRAIA Secretariat) for his valuableadvice and for the time and support received from the Secretariat office.

References
Hashimoto, 1984, Japan Ergonomics , Japan Industrial Safety & Health Association
ISO5149-1, 2, 3, 4/FDIS, ISO Website,
2014, http://www.iso.org/iso/home/store/catalogue_tc/catalogue_tc_browse.htm?commid=50362
JRAIA, 2012, Guideline of Design Construction for Ensuring Safety against Refrigerant Leakage from Multi-split
System Air Conditioners, JRA GL-13
Kataoka et al., 1999, Experimental and Numerical Analyses of Refrigerant Leaks in a Closed Room, ASHRAE
Transact., Vol 105, Pt 2
Kitajima, 2010, Actual Survey on the Air Environment at Various Number of People in Karaoke Rooms, Shibaura
Institute of Technology,
Mukaidono, 2009, Concept of Safety, Trends in Academic, Sep., P14
Nomura, 2010, Actual Survey of the Air Environment of 20 Karaoke Box Stores in Tokyo, Shibaura Institute ofTechnology
Public Buildings Association, 2006, Design Criteria for Building Facility Compiled by MLIT
Simplified Simulation Model, 2011, Progress Report by VRF SWG
The Building Standard Act, Article 28
The Building Standards Act, Order for Enforcement, Article 20, 2
Yao et al., 2000, Risk Assessment of Room Air Conditioner using R290, International Symposium on Environment andAlternative Refrigerants 2000, Kobe106

8.3 Chiller SWG: Chiller Risk Assessment and Guideline Establishment
8.3.1 Introduction
The heat-source system supplying hot or cold water to an air-conditioning system uses the hydrofluorocarbon(HFC) refrigerants R410A or R134a. Both refrigerants have a significant impact on global warming with a GWP
exceeding 1000. Therefore, it is necessary to ultimately replace them with low GWP alternatives. Some refrigerants
with a low GWP, such as R1234yf, R1234ze (E), and mixed refrigerants, have been evaluated in retrofit andperformance tests. All of these low GWP refrigerants are mildly flammable. Risk assessments (RAs) of chillers, inwhich these two refrigerants and R32 were added, have focused on the ignition and burning characteristics of therefrigerants, and have been performed to evaluate security against fire accidents and burns.
The WG (chiller SWG), which consists of professional chiller engineers, was established by the Japan Refrigeration
and Air Conditioning Industry Association (JRAIA) to perform RAs. Requirements for the chiller design and thecondition of facilities that incorporate the measures and the actions defined by the RAs will be established as a
JRAIA guideline (GL) in 2014. Progress toward this end is summarized in this report.
Table 8.3.1 Risk assessment process chart of chiller SWG
2011
The
process

Extraction task
ＦＴＡ (draft)

Details of
the process

2012
1st risk assessment

Establishmentof GL

ＦＴＡ fixed

FTA form

Condition of refrigerant
fixedleakage analysis
Extraction
special task

2013/2014
2nd riskassessment

comm
ittee

Calculation

inspection

Probability of
flammability
Treatment
Risk assessment
Proposed measures study measures

8.3.2 Scope
The scope of these requirements mainly includes air-cooled heat pumps installed outdoors and water-cooled chillers
installed in a machine room as a central air-conditioning heat source, with the exception of mobile facilities andthose with a cooling capacity ranging from 7.5 to 17,500 kW.

8.3.3 Prerequisite for performing risk assessments
Because the equipment has the same structure and potential applications as conventional equipment, the RAs1,2) thathave been performed are generally effective. The RAs have been performed in a manner that has improved theirconsistency and has focused on the differences in the flammability characteristics of refrigerants. In addition, we
have referenced studies of the mini-split air conditioner and the multiple packaged air-conditioning unit system, forwhich RAs have been performed.

8.3.3.1 Risk map
Risks were clarified using the FTA method and a numerical evaluation was performed by plotting a risk map (Rmap) (Fig.8.3.1) based on the probability of occurrence and severity of harm of each probable ignition source andcase of refrigerant leakage. If a risk level was in the A or B region, measures and actions to reduce the probability ofoccurrence and the severity of harm were suggested to shift the risk level to the C region.

(1) Probability of occurrence
The stock of water-cooled chillers and air-cooled heat pumps in the Japanese market is estimated to be 134,000
units according to JRAIA shipment statistics. This represents less than one-thousandth of the stock of mini-split
air conditioners. The probability of the occurrence of harm, based on the handbook3) (HB), is described in Table
8.3.2.

(2) Severity of harm
The severity of harm is based on the definition of fire in the HB3) (Table 8.3.3).

107

Probability of occurrence of harm

5

4

3

2

1

0

Frequent
consumer goods:10-3
industrial-level product:10-1(cases/units per year)
Probableconsumer goods:10-4
industrial-level product:10-2(cases/units per year)
Occasional
consumer goods:10-5
industrial-level product:10-3(cases/units per year)
Remoteconsumer goods:10-6
industrial-level product:10-4(cases/units per year)
Improbableconsumer goods:10-7
industrial-level product:10-5(cases/units per year)
Incredible
consumer goods:10-8
industrial-level product:10-6(cases/units per year)

Industrial-level product （adoption）
Number of accidents :once a year
(per 10 units)probability of occurrence →of harm

10 1

Table 8.3.2 Probability of occurrence of harm

Number of accidents :once a year
(per 100 units)

Frequentcases/units per

13

24

27

29

30

year

12

20

23

26

28

Occasional 1.06×10-3

10

16

19

22

25

Probable10-2

Remote1.06×'10-4

6

9

15

18

21

Improbable

1.59×'10-5～
7.94×'10-6

3

4

8

14

17

Incredible

1.59×'10-6～
7.94×'10-7

1

2

5

7

11

0

Ⅰ

Ⅱ

Ⅲ

Ⅳ

R-map
(ISO/IEC Guide51（JIS Z 8051）)

None
（No
injury）

Number of accidents :134 times a year

Negligible

Marginal:(Fire and(Smokeignition ofgeneration
product・of product・
Mild
SCART)
impairment)

Critical:(fire・
Serious
injury)A region：25～30
Intolerable
B region：14～24
Acceptable(If the risk is as low asreasonably
practicable.)
C region：1～13
Acceptable

Catastrophic:(Death,Permanent
fault,
Fire(Fire ofbuildings))

severity of harm →Fig.8.3.1 Risk assessment map
Number of accidents :14 times a year

Number of accidents :once or twice a year

Number of accidents :once or twice every ten years

Table 8.3.3 Severity of harm
Ⅳ
Ⅲ
Ⅱ
Ⅰ
０

Qualitative
representation
Catastrophic
CriticalMarginal
Negligible
None

Severity of harm
Building fires
FireFire and ignition of product
Smoke generation of productNo injury

8.3.3.2 Definition of life stages
The term “Overhaul” has been added to the life stages in the existing reports1,2), with six life stages defined:“Logistics,” “Installation,” “Usage,” “Repair,” “Overhaul,” and “Disposal.” Each life stage is distinguishable for awater-cooled chiller or air-cooled heat pump, based on the installation conditions.

8.3.3.3 Evaluation according to the risk-assessment list
In the study, risks were quantified using the risk-assessment list. Combinations of extracted ignition sources andcauses of leakage were listed for each life stage of the equipment. A risk evaluation using the R-map and theevaluation of the hazard level of different areas using JISC60079-10 was conducted simultaneously. The treatmentof the extracted risk was expanded to the GL. Then, combinations with a sufficiently low risk of ignition andleakage were eliminated, allowing combinations with a greater risk to be fully evaluated.
The intrinsically safe design and requirements to be fulfilled where a risk was identified, as well as the facility
requirements in KHK0302-25), JISC60079s4), and ISO5149-36), were specified to determine the actions to be takenin the GL.

8.3.4 Settings used in the flammable space analysis model in the event of a refrigerant leakFor safety assessments, the time that flammability persisted for and the volume of the flammable space were
calculated when a refrigerant leaked.

8.3.4.1 Analysis model of a machine room(1) Definition of a machine room
A water-cooled chiller is normally installed in a machine room. Even if an inert gas is charged in the units, theventilation system is installed in accordance with the technical standards5,6,8) to avoid the danger of suffocation.
The restriction of the ventilation volume and the installation of ignition sources as in the standards were applied tothe analysis model.

(2) Area of the machine room
The mean, minimum, and maximum values of the machine room area for a specific chiller volume aresummarized in the List of Completed Facility Research of the Journal of Heating and Air-Conditioning SanitaryEngineering (2007 - 2010) (Fig.8.3.2). In the analysis model, the area of the machine room is defined as theaverage value and the height of the machine room is defined as 5 m.

108

(3) The position of installed equipment
The shape of the machine room floor was a 1:2 rectangle. The chiller was assumed to be installed on one half of thefloor and auxiliaries were installed on the other half. The maintenance space was 1.2 m or more on the front of thecontrol panel and 1.0 m or more on the other sides (Fig.8.3.3).

(4) Assumption of ventilation volume, air supply, and exhaust louver area
The air was ventilated five times or more per hour by mechanical forced ventilation.9). The air supply andexhaust louver area were determined by reference to the “Mechanical Equipment Construction Edition” of the
Kagoshima Prefecture Building Standards. An air-supply port was installed immediately above the body of theequipment and an exhaust port was located on the wall behind the equipment (Fig.8.3.3).

(5) Refrigerant leakage point
It was presupposed that a refrigerant leakage point was located 0.15 m from the floor, which is the center of thefront face of the machine. Refrigerant leakage occurred through a 0.1-m cylindrical nozzle at sonic speed.
Suction port

1.245m

1500
1400

Machine room area （m2/kW）

1300

1.245m
0.88m

0.88m

1200

upper limit

1100

y=0.360x

5.0m

Averagey=0.128x

The target
machine

1000

Exhaust port

900
800

The target 1.01m
machine

3.3m

700
600

6.6m
Exhaust port

500
400

1.01m

Leakage point

1.21m

300
200

lower limit

100

y=0.037x（Side of Control panel）

1.28m

0.88m

1.28m
6.6m

0.1m

0
0

2500

5000

7500

10000

0.15m

Capacity （kW）

（floor surface）

Fig.8.3.2 Relationship between machine room area
and chiller capacity

Fig.8.3.3 Outline of the machine room

8.3.4.2 Analysis model of equipment installed outdoors
Wall B： back side
Wall A： right side

Air空気熱交換器面
heat exchanger

Wall D： left side
Wall C： front side

Leakage point①

Bottom panel
下部パネル面

10mm

Leakage point②

2m

Fig.8.3.4 Air-cooled chiller analysis model
Compared to a water-cooled chiller installed inside the machine room, an air-cooled heat pump installed outdoors,
without walls on all four sides, has less chance of forming a flammable space. Therefore, based on thesoundproofing installation procedure described by the manufacturer, the analysis model included two walls (Wall A
and B) and two walls (Wall C and D) with a 25% aperture ratio, thus creating an environment in which a flammablespace is most readily formed (Fig.8.3.4).
The refrigerant leakage areas were:(1) Air–heat exchanger(2) Inside the decorative panel of the unit

109With regard to (2), after a refrigerant is placed inside the panels, it could leak into the area outside the unit. The
parts inside the heat pump were also considered to be an ignition source.

8.3.4.3 Definition of the flammable region and the amount of leaked refrigerant
The representative physical properties of the three target refrigerants are shown in Table 8.3.4. The leakage areasof a chiller are the same structure and size as in a multiple packaged air-conditioning unit system. Therefore, theleakage rate was determined in accordance with JRA GL-138) (Table 8.3.5).
Table 8.3.4 Flammability of refrigerants10)

Table 8.3.5 Type of leakage flow

Stoichiometric Limit of flammability Maximum Combustion Diffusion
concentration
burning rateheat
coefficientvol%
LFL vol% UFL vol%ｃｍ/ｓ
106J/kg
cm2/ｓ
※4
R32
17.36
13.5
27.5
9.3
0.135
6.5
dry air
7.75
6.7
11.7
1.6
10.3
R1234yf
0.075
wet air
7.41
5.15※1
13.6※15.9※210.8※3dry air
10.2
R1234ze(E)0.074※3wet air
5.9※1
12.6※15.2※2
10.7※1 absolute humidity：0.016, ※2 absolute humidity：0.03, ※2 absolute humidity：0.052※4 microgravity

Leak Rate

R32
R1234yf
R1234ze(E)Probability of occurrence

Position of occurrence

Slow leak
1kg/h or less
0.9kg/h or less
0.7kg/h or less
It is unknown
whether it iscapable ofdetectingType of refrigerant leak
Rapid leak
Rapid leak
10kg/h75 or 200kg/h
8.9kg/h67 or 178kg/h
7.3kg/h54 or 145kg/h
Occasional

RemotePinhole, Welded
Slipping-out
Cracking flare
part,
accident from flare, Flare welding part
Brazing part,
fitting joint, Cauterization partcauterization part
, Pipe fitting

8.3.4.4 Analysis of the flammable space for a refrigerant leak
(1) Analysis for a machine room
An evaluation was performed for the cases shown in Table 8.3.6.
a) Case 1: To calculate the time period from the start of a refrigerant leak until it is ventilated, a non-stationary
analysis was performed for a burst leak. In addition, the difference between the R32 and R1234ze(E) refrigerants
was also evaluated.
b) Case 2: The same leakage was considered, but by changing the level of ventilation, the formation of a flammablespace was calculated (stationary analysis). Here, regardless of the refrigerant charge, the relationship between the
flammable space and the level of ventilation was evaluated by infinitizing the refrigerant leakage time.

(2) Analysis for outdoor equipment
To calculate the probability of the presence of a flammable space, a non-stationary analysis was performed. The
analysis conditions are described in Table 8.3.7.
Table 8.3.6 Analysis conditions (Machine room)
No
A
NonB
Case1 stationaryCanalysisD
Stationary A
Case2
analysis B

Table 8.3.7 Analysis conditions (Air-cooled chiller)

Ventilation Airflow
Machine room
Type of leak
Refrigerant
rate
rate
area [m2][kg/h][1/h][m3/h]
1
109
R1234ze(E)
2
218
Burst
5
545
22
54
leak
R32
2
218
1
109
R1234ze(E)
2
218

No
1
2
3
1
2
3
4

Leakage
Capacity
Refrigerant
point
[Hp]
Point①

Point②

R32
R32
R1234yf30

30

Refrigerant Wind
chargevelocity[kg/h][kg][m/s]
slow leak1
11.7
0
rapid leak 10
burst leak 75
slow leak1
rapid leak 10
11.7
0
burst leak 75
rapid leak 8.9Type of leak

8.3.4.5 Refrigerant leak analysis results(1) Analysis of the machine rooma) Case 1
The variation of the refrigerant concentration at each evaluation point over time (ventilation rates of once/h andtwice/h) is shown in Fig.8.3.5. The refrigerant concentration increased over time from the start of the leak andreached a maximum at the cessation of the leak at all evaluation points. At the cessation of the refrigerant leak, thearea from the floor to the height of the machine was a flammable region with a volume of 27 m3 at a ventilation rateof once/h. However, at a ventilation rate of twice/h, a flammable space formed only in the area adjacent to theleakage point and the refrigerant concentration in this space only reached the LFL or lower. The time thatflammability persisted for and the volume of the flammable space is shown in Table 8.3.8. In the flammable space,
the refrigerant concentration extended between the LFL and the UFL and burning velocity constraints were nottaken into account. From Table 8.3.8, if the air exchange rate was twice/h, the time that flammability persisted forand the volume of the flammable space was very low. Therefore, considering the velocity of the refrigerant, thepossibility of ignition was small. A similar analysis with the refrigerant, R32 was performed at a ventilation rate oftwice / h. The time that flammability persisted for and the volume of the flammable space is shown in Table 8.3.8.
From a comparison of the results for R32 and R1234ze(E), it can be seen that R32 was present at a higher density in

110109109m3/h
m3/h (once/h)

14%

H=100mm
H=400mm
H=1000mm

Released time

12%
10%

UFL 9.5vo%

8%

Concentration
R1234ze ofinthe[vol%]
R1234ze concentration
airair[vol%]

Concentration
R1234ze ofinthe[vol%]
R1234ze concentration
airair[vol%]

the flammable space and was easily diffused, but because the concentration required to meet the LFL was high, theflammable space was reduced.
The alteration in volume of the flammable region at a ventilation rate of once/h to form a flammable spacewith/without consideration of the burning velocity is shown in Fig.5.4.6. An R1234yf flow rate of 1.5 cm/s was usedas the burning velocity of R1234ze. The flammable space during the leak formed by centering around the area where
the air velocity was faster than the burning velocity in the neighborhood of the leakage point. Therefore, theflammable space with consideration of burning velocity was very small compared to the situation where the burning
velocity was not considered.
However, the flammable spaces have approximately the same volume regardless of the burning velocity because
the air velocity throughout the machine room was low after the leak stopped. Therefore, the evaluation was
performed in the flammable space without considering the burning velocity.

H=200mm
H=600mm

LFL 7.5vo%

6%
4%
2%
0%
0

600

1200

1800
2400
Time [sec]

3000

3600

218 218m3/h
m3/h (twice/h)

14%
12%

Released time10%

H=100mm
H=400mm
H=1000mm

H=200mm
H=600mm

UFL 9.5vo%

8%

LFL 7.5vo%

6%
4%
2%
0%

0

600

1200

1800
2400
Time [sec]

3000

3600

Height from the floor
H=1000

1000

1010

H=600
H=400
H=200
H=100

Point
1～5

Air changes
per hour(Ventilation
air volume)

No

3

A
Case1

B
C
D

(m /h)
1
(109)
2
(218)
5
(545)
2
(218)

Time

Volume offlammable area

Time × Volume

Maximum Average
min

3

m

3

3

m

m ・min

56

27

6.4

36

26

8.90E-04

2.70E-03

7.10E-0225

3.30E-04

2.70E-03

7.90E-04

26

2.80E-05

1.70E-05

4.50E-04

Volume of flammability [m3]

Table 8.3.8 The results of the non-stationary analysis

Volume of the flammable area [m3]Fig.8.3.5 The results of non-stationary analysis (variation of concentration over time)
109 109m3/h
m3/h (once/h)30

Ref. concentration
Ref. concentration + Burning velocity

25
20

Released time

15
10
5
0
0

600

1200

1800
Time [sec]

2400

3000

3600

Fig.8.3.6 The results of non-stationary analysis(variation of concentration over time)b) Case 2
The results of the stationary analysis are shown in Fig.8.3.7. The red sections in Fig.8.3.7 indicate the LFL. At aventilation rate of once/h, the LFL extended to the height of the machine and the space from the floor to the heightof machine was above the LFL. At a ventilation rate of twice/h, the flammable space was only adjacent to theleakage point. As a result, this case, which infinitizes the amount of refrigerant required to fill the space, had thesame tendency as case 1. The flammable space formed only in the area adjacent to the leakage point at a ventilation

111

rate of twice/h, and the refrigerant concentration of the other spaces was below the LFL. Therefore, the possibility ofignition was small.
As a result of the analyses of a) and b), and in consideration that an ignition source was not present at the leakage
point, the possibility of ignition was very low for an average machine room designed to the ISO51497) standard,
which specifies a mechanical forced ventilation of at least four/h. From the results of the steady-state analysis,
regardless of the refrigerant charge, there is no possibility for a flammable space to form. Therefore, it is consideredthat there should be no restrictions on refrigerant charge in the chiller GL.
However, a narrow machine room that is smaller than the average value of the machine room area (Fig.8.3.3) mustalso be considered. Because the level of ventilation is reduced and the amount of leakage over time is relatively
large even if ventilation was provided at the same level as in an average machine room, there was a possibility that a
flammable space could form. Therefore, it is necessary to add a consideration for a narrow machine room in the GL
by assuming that the minimum floor area would be 1/3 of the floor area of the average machine room. To consider
the risk when ventilation was stopped due to equipment failure or other factors, the risk of ignition was evaluated inconsideration of the presence or absence of interlock action due to the formation of a flammable space and a
sufficient refrigerant concentration.
Case 2-A) One air change per hour
Flammable region volume 9.0 m3

Case 2-B) Two air changes per hour
Flammable region volume 1.6×10-2 m3

Fig.8.3.7 The results of non-stationary analysis(2) Analysis of the outdoor equipmenta) Leakage from the air-heat exchanger
The results of the analysis are shown in Fig.8.3.8. Because diffusion was fast, a small flammable space was formednear to the refrigerant leakage point at a height of 1.13 m. Because the velocity of the refrigerant was small and theignition source was not in the immediate vicinity of the air heat exchanger, the possibility of ignition was very small.
<Leakage point ①>
Burst leak 75 kg/h, Leakage time 9 min 21 s
Time
After 30秒後
30 seconds

Tim
me
時
時間

Time
After 1 1分後
minute515mm

After5分後
5 minutes

1,130mmCut
surface
切断面

Fig.8.3.8 The results of non-stationary analysisb) Leakage from the inside of the decorative panel of unit
The results of the analysis are shown in Fig.8.3.9. If the refrigerant leaks from a decorative panel on the outdoor
equipment, it will accumulate at the bottom of the leakage point because the refrigerant is likely to have leaked froma slit in the bottom of the unit. The flammable space formed for about 1 minute. This space disappeared within one
minute once the refrigerant leak stopped. Unlike leakage from the air heat exchanger, a flammable space was formed.

112

Therefore, to assess the ignition risk, it is necessary to consider the probable existence of an ignition source. It is not
likely that ignition sources will be present in the region 50 mm above the floor surface.
With regard to the difference in refrigerants, the flammable space that formed with R32 was about two and a halftimes larger than that which formed with R1234yf. From the analysis of the outdoor unit, the use of R32 can beconsidered to be dangerous.
The results calculated for the space-time product of the flammable spaces of a) and b) are shown in Table 8.3.9.
Because this analysis was very rough, it is necessary to review the results and perform additional analysis.
<Leakage point ②>
Burst leak 75 kg/h, Leakage time 9 min 21 s
Time
After9分26秒後
9 min 26 s

model
モデル

Time
時間

Time
After10分後
10min

UFL：
0.4298Flammable
region110～60mm

LFL：
0.2181

Flammable
region80～20mm

Flammable
region30～0mm

50 mm above the floor
2,800mm

Fig.8.3. 9 The results of non-stationary analysis

Table 8.3.9 The results of stationary analysis
LeakageNo
Refrigerant
point
1
2
3
1
2
3
4

Point①

Point②

R32
R32
R1234yf

Type of leakslow leakrapid leakburst leakslow leakrapid leakburst leakrapid leak[kg/h]
1
10
75
1
10
75
8.9

Volume offlammablearea[m3]
1.60.E-07
1.16.E-05
1.40.E-04
3.48.E-03
1.54.E-01
4.02.E-01
5.66.E-02

TimeTime ×Volume

[min]
702
70
9
702
71
11
79

[m3・min]1.12.E-04
8.11.E-04
1.31.E-03
2
11
452
448

8.3.5 Basic configuration of FTA
Probability of the presence of an ignition source
Probability of ignition

Probability of ignitionat the time of distribution

Probability of ignition (#3)

Probability of the presenceof an ignition source(#1)

Probability of ignitionat the time of disposal

Probability ofthe presenceof life stages

Probability of the presenceof combustible space

Probability ofrefrigerant leak(#2)

Fig.8.3.10-a Basic FTA for each life stage

・・・

Lack ofventilation

Non-operation of the shut-off device
and detecting instrument

Fig.8.3.10-b Probability of ignition

There are a small number of operators and servicemen who can access the machine room. The room also includes
other electrical equipment with a relatively large capacity (> 5 kVA), and the installation of equipment in addition to113combustion equipment, such as a boiler, is necessary. However, unlike the situation with a mini-split air conditioner
or a multiple packaged air-conditioning unit system, a machine room and its installations can be safely controlled.
The basic FTA was configured to ensure a consistent probability of encountering refrigerant leaks and an ignition
source throughout the six life stages (Fig.8.3.10-a). In addition, a common FTA was used to assess the probable
existence of an ignition source so that it would not be overlooked in each life stage (Fig.8.3.10-b). The probability ofa leak also was studied (not shown in a figure).

8.3.6 Machine-room requirements in KHKS0302-3 and ISO5149
KHKS0302-35) is written in accordance with related standards such as the Refrigeration Safety Regulations, which
are based on the High Pressure Gas Safety Act. To maintain the safety of the machine room, standards are applied
concerning (1) ventilation through an opening or the installation of mechanical ventilation, (2) the additional
installation of safety valves and gas-release tubes, (3) explosion-proof lighting to ensure adequate performance, and(4) fire prevention/extinguishing systems.
The most important difference between KHKS and ISO5149-3 (2014 version) is the ventilation volume prescribed.
Whereas KHKS calculates the volume using the legal term “ton of refrigeration,” ISO5149-3 uses the refrigerant
filling volume. Section 3.2.3 (Prevention of Stagnant Refrigerants) of KHKS states that “The machine room must be
maintained in a way such that the concentration of refrigerant does not exceed its limit concentration even in theevent of a leak of its entire amount.” If the subsequent formula used to calculate the amount of refrigerant used isbased on the ton of refrigeration, the difference in the compression method causes the ventilation volume of amachine with the same amount of refrigerant to be different. Therefore, ventilation standards that are independent of
the refrigerant charge of the instrument will be used in the GL, but the refrigerant charge will be used as required.
Another significant difference between KHKS and ISO5149-3 regards the standards adopted for the installation ofignition sources in a machine room. ISO5149-3 specifically prohibits the presence of open flames but has nosurface-temperature standard for the equipment inside a machine room. For the GL, a surface-temperature standard
based on the RAs will be necessary.
The GL will set a new standard regarding mildly flammable refrigerants (using KHK facility criteria, if possible)
based on basic property data and leakage simulation.

8.3.7 Estimation of the probability of a refrigerant leakage accident
To estimate the probability of a refrigerant leakage accident, the following were investigated:(a) Accidents occurring in 2010 that were listed in the High Pressure Gas Safety Act.
Types of target equipment and refrigerant leakages (burst/rapid/slow) were extracted.
(b) The number of refrigerant leak accidents investigated by each committee participating in the chiller SWG.
The number of refrigerant leakage accidents that occurred at each company participating in the SWG wasinvestigated. In addition, by taking into consideration the number of chillers in stock as a proportion of the volumeof shipments made by each company, the ratio of the number of chillers experiencing an accident to the number ofin-stock chillers in the market was calculated.
The ratios obtained from the two investigation results generally matched. Therefore, the probability of an accident
was calculated based on the result of (b). The result calculated was as follows:
Burst leak: 1.0 × 10-5/chiller per year [Improbable]
Rapid leak: 1.6 × 10-4/chiller per year [Remote]

8.3. 8 Legal handling of ammonia
Ammonia is a gas typically used in mildly flammable refrigerants. Its upper explosive limit is 28 vol% and its lower
explosive limit is 15 vol%. As with the refrigerants subject to the RAs, it has mild flammability. This chapter
summarizes the handling of ammonia according to the Refrigeration Safety Regulations.

8.3.8.1 Refrigeration Safety Regulations
Ammonia is listed as a flammable gas and as a toxic gas in Article 2 of the Refrigeration Safety Regulations. Basedon these characteristics, a technical standard to determine its handling has been specified. The handling of
flammable gases can be summarized as follows:114

(1) The structure of the machine room shall be such that it is free of any stagnant gas in the event of a refrigerantgas leak (Article 7, item 3).
(2) The location of the opening of the release tube for safety valves and similar equipment shall be appropriate to
the properties of the refrigerant gas (Article 7, item 9).
(3) The liquid level measurement instrument shall not be a round glass level instrument. For a glass tube
instrument, breakage prevention measures and leak prevention measures in the event of breakage shall betaken (Article 7, items 10 and 11).
(4) In accordance with its scale, appropriate fire extinguishing equipment shall be installed in appropriate
locations (Article 7, item 12).
(5) The electrical equipment within refrigerant equipment shall be structured such that it has an explosion-proof
capacity appropriate to the installation location and type of refrigerant gas (flammable gases excluding
ammonia) (Article 7, item 14).
(6) Leak-detection equipment shall be installed in any location where stagnant gas may occur (Article 7, item 15).
(7) Measures shall be taken to remove refrigerant gases in a safe and quick manner (Article 7, item 16).
(8) Measures shall be taken to prevent any danger at the time of maintenance (Article 9, item 3 (b)).

8.3.8.2 Exclusion from the application of Article 7, item 14
Ammonia is excluded from the application of item (5) (Article 7, item 14). This exclusion is in accordance with thetechnical reference11). An experiment was conducted to determine: 1) the concentrations that define the explosive
limits in which a gas easily ignites, 2) the amount of ignition energy generated if it ignites, 3) the spatial distributionof explosive concentrations, and 4) the connection between the ignition frequency and time. The reference states thatthe validity of the Refrigeration Safety Regulations was reconfirmed based on factors 1) to 4).
Accordingly, in this SWG, the validity of the explosion-proof capacity was also evaluated by focusing on factors 1)to 4) as a guideline.

8.3.9 Derivation of ignition probability
The probability of ignition was derived by the following procedure.

8.3.9.1 Surface temperature of equipment in the machine room
Among the machines and instruments installed in the same area as the target equipment, those listed below, whichhave relatively high surface temperatures, were investigated.
1) Heat source unit (e.g., boiler)2) Electric motor drive (e.g., pump motor)
3) Ventilation (e.g., ventilation fan)4) Lighting apparatus (e.g., fluorescent light, incandescent lamp)
5) Heating appliance (e.g., electric heater)
The results of ignition tests using mildly flammable refrigerants12–14) performed at locations such as Tokyo
University of Science, Suwa, and the National Institute of Advanced Industrial Science and Technology will becompared to the surface temperatures of equipment inside the machine room to specify the surface-temperature
limits inside a machine room.

8.3.9.2 Smoking rate
Burning cigarette ends and lighter/match flames can be considered to be ignition sources. Therefore, the smoking
behavior of servicemen was investigated.
- Fifty-three percent of the servicemen smoked and 28% had smoked on-site. During the past year, 7% of allservicemen sampled had smoked on site.
- A lighter is used as the ignition source by 99.6% of smokers while 0.4% use a match.
Assuming that the proportion of servicemen that smoke on site is 7%, the number of cigarettes smoked perperson per day is 19.115), the working hours per day are 8, the ignition source is only a match, and the time whenan open flame exists per smoking event is 2 s, the probability (ignition frequency) of an ignition source existing
because of smoking is estimated to be of the order of 10-8 to 10-9.

8.3.9.3 Electrical components

115

Among the electrical components (e.g., electric motor drive, electromagnetic switch, electromagnetic contactor,
printed-wiring board, and transformers) to be mounted on a chiller unit, an electromagnetic contactor, in which an
arc is generated, has the greatest possibility of providing an ignition source. The rating capacity of each type ofelectromagnetic contactor and the capacity (horsepower) of the chiller have been summarized.
There is a wide range of chiller capacities among the target equipment and the electromagnetic contactors used also
have a wide range of capacities. For a product with 20 horsepower or less, the capacity is generally less than 5 kVA.
Electrical components with capacities less than 5 kVA are not considered to be ignition sources, as agreed by other
SWGs. This evaluation therefore focuses on components with a capacity of 5 kVA or more.
There is no electrical component with a capacity of more than 5 kVA in the control system of a product with morethan 20 horsepower. To estimate the maximum risk, an electrical component with a capacity of 5 kVA or more isassumed to always be an ignition source following its first startup/shutdown. Assuming that the maximum numberof startup/shutdown cycles per day is 6/h (screw chiller) or 2/h (centrifugal chiller) and that the time that theelectromagnetic contactor is present is 1 s, the probability of the existence of an ignition source, is estimated to be of
the order of 10-4. Compared to the flame from a match, this probability is large and therefore a further detailed study
will be conducted.

8.3.10 The relationship between the RA and GL
To determine the probability of the presence of a flammable space, the ignition probability at each life stage wascalculated (assuming there was no ventilation and that ignition sources always ignite). The results are shown in
Table 8.3.10. The sum of the probability of occurrence of fires and burns is more than 10-6. Therefore, it is necessary
to take measures to reduce the probability to a level that is considered acceptable by society. This represents thestandard for ventilation and the system of holding by it.
Table 8.3.10 Risk assessment results
Accident
scenario
Logistics
Installation
Usage
Repair
DisposalLife stage
Probabillity
Assessment
probability (cases/units per year)
3.22x10-7 X
0.0564
Safe
Time × Volume
5.01x10-7 X
0.0564
Safe
Time × Volume
3.82x10-6 X
Nearly0.7809Time × Volume
safe
2.73x10-6 X
Nearly0.2523Time × Volume
safe
1.38x10-6 X
0.0565
Safe
Time × Volume

The items to be added are as follows:- There is a wide-range of equipment conditions (such as transfer, storage, etc.) in the distribution process. Large
warning stickers should be used, indicating that a slightly combustible gas is present and detailing its handlingprocedure.
- It is necessary to clarify installation conditions for outdoor applications because of the airflow.
- An electromagnetic contactor (< 5 kVA), which is within the scope of IEC60335-2-407) is not regarded as an
ignition source on the basis of the results of the mini-split SWG.
- There is no technical standard specifying a chiller unit with a structure in which a refrigerant gas may
accumulate due to a decorative panel or other design features. The requirement for an opening space, which does
not have enclosed structure, is described in the GL as an intrinsically safe design.
- With regard to disposal, a risk assessment should be undertaken focusing on refrigerant recovery.

8.3.11 Guideline planning taking IEC60079-10-1 into consideration
8.3.11.1 Principle of IEC60079-10-1
The following principle from IEC60079-10-1 is crucial: “Installations in which flammable materials are handled orstored should be designed, operated and maintained so that any releases of flammable material, and consequently theextent of hazardous areas, are kept to a minimum, whether in normal operation or otherwise, with regard to
frequency, duration and quantity.”

116

The classification of hazardous areas in which a danger may arise due to a flammable gas is defined in IEC6007910-116). Areas can be categorized into one of three hazardous and non-hazardous areas based on their grade ofrelease and two indexes of the ventilation condition: “degree of ventilation” and “availability of ventilation” (Table
8.3.11). In Japan, the classification of hazardous areas is established in JISC60079-104), which is the same as that
established in IEC60079-10-116). In the chiller SWG, a study was conducted using JISC60079-10.
Table 8.3.11 Influence of independent ventilation on the type of zone
Ventilation
DegreeGrade ofreleaseHigh

MediumLow

Availability
Fair

Poor

Good, fairor poor

Good

Fair

Poor

Good

Continuous

Nonhazardous

Zone 2

Zone 1

Zone 0Zone 0 + Zone 0 +Zone 2
Zone 2

Primary

Nonhazardous

Zone 2

Zone 2

Zone 1

Zone 1 + Zone 1 + Zone 1 orZone 2
Zone 2
Zone 0

Secondary

NonNonhazardous hazardous

Zone 2

Zone 2

Zone 2

Zone 2

Zone 0Zone 1and even
Zone 08.3.11.2 Guideline planning taking IEC60079-10-1 into consideration
In Japan, when a flammable gas is used in a chiller, the technical standard, JISC60079s4), and the Refrigeration
Safety Regulations (Article 7, item 14) must be complied with, and the use of explosion-proof electric equipment isnecessary. However, the relationship between the equipment installation standard to be referenced (KHK0302-35) orISO51496)) and JISC60079s4) is not specified. Although JISC60079s4) specifies that explosion-proof equipment is
not required in a non-hazardous area as determined by the availability-of-ventilation, this seems to be consistent
with the fact that a mildly flammable refrigerant is not considered to be a flammable gas in the Refrigeration Safety
Regulations.
Therefore, the conditions for implementing an RA, the techniques used, and the results obtained will be reported in
the SWG. In addition, these will be applied to the requirements for the intrinsically safe design of the equipment in
the GL, which is being established incorporating equipment installation requirements that do not require the settingof hazardous areas, in accordance with the principle of JISC60079s4). The basic policy adopted and tasks required in
the preparation of the GL are as follows.

8.3.11.3 Basic policy adopted in the guideline
The GL is being prepared by suggesting measures to take against risks identified by the RA to KHKS 0302-3 andincorporating the necessary sections of ISO 5149-1, 3. The basic policy adopted in the GL is as follows:- Only one slightly combustible refrigerant (A2L) is referred to as the target refrigerant and descriptions of theapplications of other refrigerants will be deleted.
- The following measures should be adopted with reference to IEC60079 so that a machine room does not becomea hazardous area, even if a refrigerant leaks.
(1) Installation and inspection of ventilation devices (including backup with multiple devices as required).
(2) Refrigerant detector (including UPS and periodical inspection).
Note: The following is under debate in the SWG.
- Outdoor installation should be considered to be a non-hazardous area following an analysis.
- Electrical equipment should have a non-explosion- proof specification and conform to IEC/ISO.
- Specific values (twice or more/h ventilation, scope of a hazardous area) must be determined on the basis of
the results of the analysis.
- Firearms are classified as either work firearms or other firearms (conforming to ISO) and must be consideredin the risk assessment, with the exception of the construction period.

8.3.11.4 Tasks for establishing a guideline
The following are the tasks required to establish the GL. The GL is described as a means for reducing the risk andwill be established within 2014.
1) Rule of recovery after long-term suspension- An evaluation at the time of restart if a refrigerant leaks during long-term suspension is under consideration.
2) Rule of outdoor installation in consideration of IEC60079.
3) A method to consider spontaneous ignition temperature117

- The spontaneous ignition temperature is being considered with regard to the limits of an open fire in amachine room according to ISO5149 and the limitations of the equipment surface temperature.
4) Rule to establish a refrigerant detector- A comparison of ISO/GL-13 to determine adequate regulations is under consideration.
(1) Power supply (alarm, detector): Installing an independent power supply and UPS is desirable.
(2) Target to detect: This should be refrigerant concentration rather than the oxygen concentration(RCL standard).
(3) Setting values: To conform to ISO and GL-13.
(4) Interlock: Although the adoption of an interlock is under consideration with reference to IEC60079, if therisk is low, an interlock will not be adopted.
5) Control of refrigerant concentration (regulation of the amount of refrigerant filling)- Although KHKS demands the control of the volume of a machine room and the amount of refrigerant fillingso that the refrigerant concentration is equal to or lower than the limiting concentration, the easing of
regulations is under consideration because ventilation is presupposed in the GL.
- As a result of the stationary analysis, a regulation to specify the minimum amount of refrigerant filling in amachine room system is under consideration (no filling amount regulation).

Acknowledgments
This report was written by the author and Mr. Yosuke Mukai by compiling the research results of 10 Committee
members, as well as Mr. Masayuki Aiyama, Mr. Mikio Ito, Mr. Isao Iba, Mr. Tetsuji Saikusa, Mr. Yoshihiro Sumida,
Mr. Mamoru Senda, Mr. Takuho Hirahara, Mr. Syuji Fukano, Mr. Koichi Yamaguchi, and Mr. Tomokazu Tashimo.
Sincere appreciation is extended to the members concerned.

References
1) Report on the Result of Risk Assessment Consideration of Room Air-Conditioner with R290 Refrigerant: The
Japan Refrigeration and Air Conditioning Industry Association Environment Committee Refrigerant Global
Warming Response Commission: Summary of the Non-FC Refrigerant Consideration Session Meeting (1999).
2) “Risk Assessment of HFC-32 and HFC-32/134a (30/70wt%),” Split System Residential Heat Pump, Arthur D
Little Inc., United States (1998).
3) Ministry of Economy, Trade, and Industry: Risk Assessment Handbook Practice Edition (2011).
4) JISC60079-10(2008): Electric Machinery and Instruments Used in Explosive Atmospheres Chapter 10: Classification of Hazardous Areas.
5) KHKS0302-3: Standards of Refrigeration and Air-Conditioning Equipment Facilities [Facilities with Flammable
Gases (including low-flammable Gases)], (2011).
6) ISO5149: Refrigerating Systems and Heat Pumps – Safety and Environmental Requirements, (1993)
Part 1) Definitions, classification and selection criteria
Part 2) Design, construction, testing, marking and documentation
Part 3) Installation site
Part 4) Operation, maintenance, repair and recovery.
7) IEC60335-2-40: Household and Similar Electrical Appliances -Safety-, (2005)
Part 2-40) Particular requirements for electrical heat pumps, air conditioners and dehumidifiers.
8) JRA GL-13: Guideline for Ensuring Safety in the Event of a Refrigerant Leak from a Multi-Unit Air
Conditioning System, (2011).
9) ASHRAE15: Proposed Addendum to Standard 15-2010, Safety Standard for Refrigeration Systems, (2010).
10) Assessment of flammability of R-1234yf and R-1234ze(E): The 49th Combustion Symposium (2011/12).
11) T. Toyonaka: “Refrigeration,” 70 (811), 5 (1995).
12) T. Imamura: Evaluation of Fire Hazards of A2L Class Refrigerants, The International Symposium on New
Refrigerants and Environmental Technology 2012, pp. 65-68, Kobe (2012).
13) T. Saburi: Combustion Characteristics of Flammable Refrigerant Gases, International Symposium on New
Refrigerants and Environmental Technology 2012, pp. 69-72, Kobe (2012).
14) K. Takizawa: Flammability Property of 2L Refrigerants, International Symposium on New Refrigerants andEnvironmental Technology 2012, pp. 73-79, Kobe (2012).
15) JT website: http://www.jti.co.jp/investors/press_releases/2012/0730_01_appendix_02.html, (2013).

11816) IEC60079-10-1: Explosive
Atmospheres - Part 10-1: Classification of Areas - Explosive Gas Atmospheres.

1199. Deregulation Activities in Japan for the Introduction of Mobile Air
Conditioning Refrigerant R1234yf
9.1 Background to R1234yf Introduction in Japan
Worldwide efforts to reduce greenhouse gases (GHGs) have resulted in a growing demand for mobile air
conditioning refrigerants with low global warming potential (GWP). Since 2011, the European Union (EU) has
banned the use of refrigerants with a GWP of greater than 150 in new-model vehicles (from 2017 onwards, theban will apply to all new vehicles). Japanese automakers are taking the necessary steps for vehicles destined for
the EU market.
Preparations for the introduction of low-GWP refrigerants are also underway in North America. The UnitedStates (U.S.)-based international Society of Automotive Engineers (SAE International) has completed a risk
assessment study on R1234yf, and the American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE) has classified R1234yf as a mildly flammable gas. In addition, on April 1, 2010 the U.S.
Environmental Protection Agency (EPA) issued GHG regulations allowing vehicles that use a low-GWP
refrigerant to be provided with credits.
In Japan, the Global Warming Prevention Measures Subcommittee under the Industrial Structure Council’s
Chemicals and Bio-industry Committee approved, on February 17, 2011, the interim course outlined during its
discussions on substitute refrigerants. Specifically, the Subcommittee acknowledged the urgent need to promoterefrigerant replacement through collaboration among automakers, government agencies, research institutes, andequipment manufacturers and recommended the resolution of various existing obstacles by 2014.
In response, the Japan Automobile Manufacturers Association, Inc. (JAMA), in concert with research institutes
and the manufacturers of refrigerant retrieval/recharging equipment, launched a risk assessment study aimed atensuring the safe and easy handling of R1234yf by automotive maintenance shops throughout Japan by thetarget year of 2014.

9.2 Obstacles to R1234yf Introduction
Table 9.1 summarizes existing obstacles to the introduction of R1234yf from the perspective of a vehicle’s life
cycle and indicates the need (or not) for measures to address them.
A special ministerial approval scheme is currently in place in Japan to facilitate the approval of factory lines
producing R1234yf-equipped vehicles based on the explosion-prevention measures taken. Because the numberof these production lines is projected to increase in step with the growing number of vehicle models
incorporating R1234yf, further deregulation of R1234yf is necessary.
With regard to after-sales servicing, operators of varying types and scale—including auto maintenance shop
operators, auto body repair shop operators, and electrical equipment repair shop operators—are engaged in the
retrieval/recharging of refrigerants for vehicles in need of repair or that were in accidents. For many of these
operators, making the large investment necessitated by regulations governing R1234yf is difficult.

120

JAMA’s Vehicle Maintenance Subcommittee has singled out requirements concerning mandatory safe distancesfrom gas cylinders as the top-priority deregulation target (see item 4 in Table 9.1 above). Regarding the handlingof R1234yf that may be generated from the dismantling of end-of-life vehicles, the Subcommittee decided not toaddress this matter in the present project because regulations on the retrieval of R1234yf at the vehicle
dismantling stage have yet to be established.
Table 9.1 Obstacles and measures required
1) Vehicle
production2) Charging
gas(after-sales
servicing)3) Storage ofcharging gas
4) Retrieval/recharging(after-sales
servicing)

Current flammable-gas explosion prevention requirements (government
ministry-approved)
No obstacles if:-Compliant with Announcement No. 139-Charging gas pressure does not exceed 0.8 MPa at 35 °C and satisfies termsof Art. 4-3 in Announcement No. 139[As per High-Pressure Gas Safety Law]
Current requirements on mandatory safe distance from fire/flammables[As per High-Pressure Gas Safety Law]
Current requirements on:-Mandatory safe distances from gas cylinders (hospitals, schools: at least 15
m; homes: at least 10 m )-Removal of static electricity, etc.
-Mandatory licensing by prefectural governments of auto maintenance shops

Deregulatory measures required
No deregulatory measures required

Deregulatory measures required
Deregulatory measures required

9.3 Activities of JAMA’s Vehicle Maintenance Subcommittee
In collaboration with the manufacturers of refrigerant retrieval/recharging equipment, refrigerant suppliers, auto
maintenance shop associations and other stakeholders, JAMA has been carrying out activities aimed at resolving
existing obstacles to the widespread use of R1234yf by 2014. One such activity was a study that used the risk
assessment mapping method to assess risk by combining the “probability of injury” and “severity of injury” in a
6 × 5 matrix. Supported by the risk assessment mapping data, JAMA will petition the government to review its
safety regulations in order to more accurately reflect the actual risks of R1234yf.
As a first step in its risk assessment study, JAMA conducted hearings with refrigerant retrieval/recharging
equipment manufacturers and a survey of retrieval/recharging operators to more clearly identify the risks atmaintenance work sites. In cooperation with the Japan Automobile Service Promotion Association, Japan Auto
Body Repair Association, and Japan Automotive Electrical Equipment Service Association, the survey
questionnaire was distributed to a representative selection of auto maintenance shops, in terms of business scaleand services offered, across Japan.
Completed questionnaires were received from a total of 756 auto maintenance shops. The information provided
by the 533 shops that performed their own retrieval/recharging operations was compiled into basic data on auto
maintenance shops (number of workers, number of vehicles repaired, shop layout information, etc.) and workers’
on-the-job observations (on refrigerant leakage occurrence, ventilation conditions, the presence of ignition
sources, etc.).
Based on the data obtained from the questionnaires on leakage-prone points, leakage amounts, and ignition
source specifications, JAMA conducted an ignition test and leak simulation test; in both instances, worst-case
R1234yf leakage conditions were assumed. The data obtained in these tests were used to calculate theprobability and severity of injury caused by R1234yf leakage and map them for risk assessment. Based on the
results of its risk assessment study, JAMA is now preparing to propose to the regulatory authorities a package of121

measures that would allow R1234yf to be treated as an inert gas (Table 9.2).
Table 9.2 JAMA’s R1234yf-related activities
Conduct of risk assessment study (NEDO* project including questionnaire-based survey; data compilationcommissioned from JARI)*New Energy and Industrial Technology Development Organization

Discussion of measures for regulatory exemption of R1234yf(Participation in METI-sponsored KHK project)
Submission of proposal for review by METI*

Apr. 2011–
Mar. 2013
Oct. 2012–
Mar. 2013
Apr. 2013–*Ministry of Economy, Trade and Industry

9.4 Ignition Test
9.4.1 Test method
The ignition test was carried out by Tokyo University of Science, Suwa, in the Hy-SEF explosive fire resistancetest facility at the Japan Automobile Research Institute’s Shirosato Test Center (Fig. 9.1).

Fig. 9.1 Overview of the Hy-SEF test facility

Based on data obtained from the survey questionnaire described above, the identified risks were classified into
four categories, as shown in Table 9.3, and prioritized according to the probability and severity of injury causedby R1234yf leakage. The two leading risks—namely, hose rupture and leakage from inside retrieval/recharging
equipment—were examined to determine the answers to the following questions:-

In the event of refrigerant leakage from a pinhole in the hose, to what extent does flammable gas escapeand aggregate? Does it cause ignition?

-

In the event of refrigerant leakage inside the retrieval/recharging equipment, is there a risk of ignition
owing to sparks from the electrical relay or other similar parts of the equipment?

Table 9.3 Risk Classification by JAMA’s Vehicle Maintenance Subcommittee
Risk Description
1) Slow leak from a junction
Hose rupture2) (including hose pinhole)

Leak Speed (amount/time)
1 kg/24 h (gas)
1 kg/60 s (gas)Cylinder safety valve activation 24 kg/1 h (gas)(fusible plug)
Leakage from (safety valve, etc.) 300 g/60 s (liquid) (initially4) inside retrieval/
100 g/0.5 s)recharging equipment
3)

122

Remarks
Ignition potential: Low
Inner diameter of hose: 4 mm
Internal pressure of hose: 0.5 MPa (at normal
temperature)
Activation possibility: Low
Activation possibility: Low

A testing space of 8 m × 8 m was secured within the test facility, and a testing apparatus (specifically, a 1 m × 1
m × 1 m acrylic box) to simulate retrieval/recharging equipment was installed inside the testing space. The
testing apparatus featured a 20 mm-wide slit on two opposing sides that could be closed or opened forventilation (Fig. 9.3).
In the hose pinhole ignition test, which was conducted in the open testing space, the refrigerant was made toleak continuously from a pinhole in the hose, and refrigerant concentrations were measured at various locations
from the pinhole. The potential for ignition was then examined by applying electric sparks (both a single sparkand repeated sparks) or a naked flame near the pinhole. In the retrieval/recharging equipment ignition test, asingle spark was discharged to examine the potential for ignition when the ventilation slits were open and when
they were closed.

Fig. 9.2 Testing space simulating a work site

Fig. 9.3 Apparatus simulating retrieval/recharging equipment1239.4.2 Test results
As shown in Table 9.4, the results of the hose pinhole ignition test confirmed that the area within a 10-cm radiusfrom the pinhole was flammable. Nevertheless, despite the application of an ignition energy of 10 J or more,which far exceeded the maximum ignition energy existing inside the equipment (1.07 J at the relay contact),
ignition could not be induced anywhere near or away from the pinhole. Similarly, in the retrieval/recharging
equipment ignition test and despite the application of a large ignition energy of 16 J, ignition did not occur; thiswas presumably because of the exchange of air between outside and inside the testing apparatus through theopened slits. As previously reported, combustion and flame propagation occurred when the slits were kept
closed; however, no blast pressures were generated.

Table 9.4 Ignition test results
Priority Risk
Hose rupture(including hosepinhole)Leakage inside
retrieval/recharging
equipment

Test Objective and Outline
Leakage from Φ4 mm hose; observation of concentration distribution andpotential ignition▪ Leak speed: 470 g/min (cylinder heated to 50 °C)▪ Ignition source: Repeated electric sparks
Leakage inside closed
1 m3 space (acrylic box) with vertical slits on two opposing sides▪ Leak speed: 380 g/min▪ Ignition source: Electric sparks (16 J, 6 Hz)▪ Temp./humidity: 25 °C, 75%

Results▪ Flammable area extending to a 10-cm
radius from pinhole▪ No ignition▪ Generation of flammable area after
leakage▪ No ignition

9.5 R1234yf Leak Simulation Test
As stated in the preceding section with regard to retrieval/recharging equipment ignition testing, leaked R1234yf
would not ignite when the slits on the testing apparatus were kept open for ventilation, even when electric sparksof a sufficiently large ignition energy were applied. An R1234yf leak simulation test was subsequently
conducted to examine this phenomenon in greater detail through analysis of the refrigerant concentrations andflow velocity inside the simulated retrieval/recharging equipment. The analytical conditions were established asfollows:-

Analysis code: PHOENICS (thermal fluid analysis code)-

Analysis model: 1 m × 1 m × 1 m cube with slits (each 20 mm wide and 1 m high) on two opposing sides-

Gas discharge speed: 500 g/min (from bottom of equipment)-

Model size: 500,000 elements (100 × 100, 50 vertical partitions)-

Calculation method: 0.5 s steps, 50 repetitions

Fig. 9.4 shows an analytical image of R1234yf concentrations during discharge. Given the known lower
flammable limit (LFL) of 6.2 vol% (JFMA, 2012), the distances of LFL and 1/4LFL from the leakage point
proved to be 256 and 964 mm, respectively. Assuming that these distances hold true in the real world, the LFL
distance of about 10 cm determined in the ignition test under review here signifies a 1/4LFL distance ofapproximately 38 cm.

124

Note: Figures on the left denote mass concentration values.

Fig. 9.4 R1234yf concentrations during discharge

Figs. 9.5 and 9.6 show R1234yf’s flow velocity 30 s after the cessation of leakage. Areas of low flow velocity
were found along the slits, where air flow velocity was moderated by the simultaneous entry and exit of air
through the slits. In most of the other areas, the flow velocity was 2 cm/s or faster and thus exceeded R1234yf’s
maximum combustion speed of 1.5 cm/s (Takizawa, 2012). This clearly demonstrates that R1234yf cannot
ignite inside a ventilated container when an air flow is present.

(Velocity display range: 0.02–1 m/s)

(Velocity display range: 0–0.015 m/s)

Fig. 9.5 R1234yf flow velocity 30 s after leakage

Fig. 9.6 R1234yf flow velocity 30 s after leakage

Cessation

cessation

9.6 Risk Assessment and Mapping
9.6.1 Probability of injury
The probability of injury was calculated based on fault tree analysis (FTA). First, unfavorable events (topevents) were identified. The routes leading to a fault or accident, as well as probability values, were thenestablished in a fault tree diagram to analyze the probability of top-event occurrence on the basis of lower-level

125events that caused the top events. A report on fault tree analysis of ignition risks at automotive maintenanceshops having already been published by the SAE (Gradient Corporation, 2008; 2009), JAMA conducted its own
fault tree analysis based on actual conditions in auto maintenance shops in Japan taking into account the SAE’s
findings.
Fig. 9.7 shows the fault tree diagram used in the risk assessment. “Ignition” was identified as the top event. For
ignition to take place, the following three events would have to occur simultaneously: (i) the presence ofrefrigerant concentrations at flammable levels or between the lower and upper flammable limits; (ii) the
execution of maintenance work under unsatisfactory ventilation conditions; and (iii) the presence of a flame
source having an amount of energy exceeding the minimum ignition energy. These three events were applied toeach of three possible leakage locations—hose junction, hose rupture, and cylinder—and their leakage
probabilities were determined on the basis of data obtained from the survey questionnaire and the ignition andleak simulation tests.

Fig. 9.7 Fault tree diagram

Refrigerant leakage (*1 in Fig. 9.7)
Probabilities of refrigerant leakage were calculated from the leakage frequency data obtained from thesurvey questionnaire.
(b) Deficient ventilation (*2 in Fig. 9.7)
Fact 1: Presumably because ventilation is required by law, no survey questionnaire respondents answeredthat they had handled refrigerants in the absence of ventilation. Fact 2: The results of the ignition and leak126

simulation tests confirmed that, because the flow velocity of the leaked refrigerant exceeded its maximum
combustion speed in the presence of ventilation, no stable flames would be generated inside an indoor
facility or a container with slits. In light of these facts and the impracticality of assuming that there is no air
flow at auto maintenance shop work sites in Japan, the probability of deficient ventilation was rated at 10-8.
(c) Ignition source inside flammable area (*3 in Fig. 9.7)
In the ignition test, no stable flames were generated by 16-J sparks even in the flammable area within a
10-cm radius from the pinhole. This was presumably because air was stirred by convection in the indoor
test facility. Moreover, it is hard to conceive that trained maintenance technicians would handle a heater,
welding machine, or other similar ignition source within 10 cm of a flammable refrigerant. In the case of
retrieval/recharging equipment, the compressor-driven relay contact was the ignition source with thegreatest ignition energy. Because most of the relay body was sealed from the atmosphere by a cover and thequenching diameter (i.e., maximum diameter of a hole through which flames do not pass) for R1234yf is 7–
8 mm, it is unlikely that flames would propagate even if ignition occurred at the relay contact. Thus, theprobability of the presence of a significant ignition source (to enable combustion) was rated at 10-8.
(d) Ignition
Based on the observations and calculations described above, the probability of ignition was considered to be
1 × 10-18 for refrigerant retrieval/recharging equipment. This probability is unthinkably low compared to thestandard probability of 10-8 assigned to relays in the guidelines introduced by the Union of Japanese
Scientists and Engineers’ R-Map study group.

Fig. 9.8 Retrieval/recharging equipment relay configuration (general-purpose model)

9.6.2 Severity of injury
The severity of injury was derived from the ignition test results related to physical criteria (i.e., heat- andpressure-related factors including flame temperature, radiant heat, and sound pressure) and chemical criteria (i.e.,hydrogen fluoride concentration, which is a toxic factor). Because ignition did not occur in the test setups
simulating a maintenance work site and the inside of retrieval/recharging equipment, no heat, pressure, or
toxicity was generated. Consequently, the severity of injury was rated at zero—i.e., no injury (Table 9.5).

127

Table 9.5 Injury at work site
Item Measured
Flame temperature
Heat
Pressure
Toxicity

Value Measured
No temperature rise

InjuryNone

Radiant heat

None

None

Sound (blast) pressure
HF concentration

None
None (0.0 ppm by densitometer)

None
None

A worst-case test was also conducted assuming the occurrence of combustion in a closed space. The test results
are summarized in Table 9.6. According to video analysis, the flame spread to a vinyl chloride side sheet 50 cm
away 1.25 s after ignition; this resulted in an estimated flame temperature of 400 °C or higher. Nevertheless, thecombustion was moderate rather than explosive and was short-lived (lasting no more than several seconds); any
injury incurred would therefore be only a slight burn, even if the flame were to come into contact with a humanbody. Because the hydrogen fluoride concentration exceeded the maximum permissible limit, a worker exposed
to it would feel a skin irritation. However, the hydrogen fluoride quickly dispersed, which would enable theworker to evacuate safely. For these reasons, the worst-case injury severity was rated at I (slight).

Table 9.6 Injury in worst-case (closed space) ignition testing

Heat
Pressure
Toxicity

Item Measured
Flame temperature

Value Measured
Not measured (video analysis: ≥400 °C)

Radiant heat

Not measured

Sound (blast) pressure
HF concentration

None (video analysis)
Exceeding maximum limit of 3 ppm

InjurySlightNone
Slight9.6.3 Risk mapping
Based on the probability and severity of injury derived in the tests described above, the ignition risk of R1234yf
during retrieval/recharging was plotted in Region C of the risk assessment map, even for the worst case (Fig.
9.9). The ignition risk of R1234yf can therefore be considered socially acceptable.

Fig. 9.9 Risk assessment map

1289.7 Progress towards Deregulation
9.7.1 Risk reduction measures
The results of the risk assessment activity described above were submitted in a report (KHK, 2013) to theCommittee for the Study of R1234yf Retrieval/Recharging Equipment Standards and Implementation (chair:
Professor Eiji Hihara of the University of Tokyo’s Graduate School of Frontier Sciences) by the High-Pressure
Gas Safety Institute of Japan as part of its research work commissioned by Japan’s Ministry of Economy, Tradeand Industry (METI).
The committee reviewed the assessment results with respect to the ignition risk of R1234yf and confirmed thatthe risk is within socially acceptable parameters. In addition, for deregulation purposes, the committee examined
the risk reduction potential of double-layer safety measures such as the application of a well-ventilated structure
to the retrieval/recharging equipment mainframe (with a fan and ventilation openings in two directions),
elimination of static electricity, restricted refrigerant storage container capacity, and the introduction of user
warning labels concerning R1234yf flammability.
The committee subsequently submitted to METI a report on R1234yf; this was then released to the public by
METI in June 2013 with the comment that, given the proposed safety measures, the R1234yf
retrieval/recharging equipment can be regarded as equally safe as the existing inert fluorocarbon
retrieval/recharging equipment which has been exempted from the High-Pressure Gas Safety Law.

9.7.2 Industrial Structure Council activity
In response to METI’s action, Japan’s Industrial Structure Council is scheduled to start discussing in March2014 the possible exemption of R1234yf retrieval/recharging equipment from the High-Pressure Gas Safety
Law.

9.8 Conclusion
As reported above, Japan has made great strides towards the deregulation of R1234yf retrieval/recharging
equipment and the promotion of a low-GWP refrigerant beginning in 2014.

Acknowledgments
JAMA expresses its gratitude to the Japan Automobile Service Promotion Association, Japan Auto Body Repair
Association, and Japan Automotive Electrical Equipment Service Association for their assistance in the
distribution of the survey questionnaire; to auto maintenance shop personnel for completing the questionnaire;
to Researcher Tetsuya Suzuki of the Japan Automobile Research Institute and Mr. Yoshisuke Kusakari of
Yamada Corporation for their advice on the risk assessment study; and to Professor Osami Sugawa and Junior

129

Associate Professor Tomohiko Imamura of Tokyo University of Science, Suwa, for their cooperation with theignition test.

References
Japan Fluorocarbon Manufacturers Association (JFMA) ed., 2012, List of CFCs, HCFCs and fluorocarbons’environmental and safety data, JFMA, http://www.jfma.org/atabase/table.html (in Japanese)
Takizawa, K., 2012. Flammability properties of 2L refrigerants, Proceedings of the International Symposium on
New Refrigerants and Environmental Technology 2012, Kobe, Japan.
Gradient Corporation, 2008. Risk Assessment for Alternative Refrigerant HFO-1234yf.
Gradient Corporation, 2009. Risk Assessment for Alternative Refrigerants HFO-1234yf and R744 (CO 2 )-Phase
III.
High-Pressure Gas Safety Institute of Japan (KHK), 2013. Report to the Committee for the Study of R1234yf
Retrieval/Recharging Equipment Standards and Implementation (prepared as part of the 2012 high-pressure
gas safety project commissioned by the Ministry of Economy, Trade and Industry for the drafting of ahigh-pressure safety standard and an implementation method).

130

Member List
Chair
Eiji HIHARA, Professor- Graduate School of Frontier Sciences, The University of Tokyo.

Associate Chair
Satoru FUJIMOTO- The Japan Refrigeration and Air Conditioning Industry Association. (JRAIA)(Daikin Industries, Ltd.)

Committee Members
Sigeru KOYAMA, Professor- Interdisciplinary Graduate School of Engineering Sciences, Kyushu University.
Osami SUGAWA, Professor
Tomohiko IMAMURA, Junior Associate Professor- Department of Mechanical Engineering, Faculty of Engineering, Tokyo University of Science, Suwa.
Chaobin DANG, Associate Professor- Graduate School of Frontier Sciences, The University of Tokyo.
Masanori TAMURA
Kenji TAKIZAWA, Senior Researcher- Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Scienceand Technology. (AIST)
Masayuki SAGISAKA, Principal Research Manager
Tei SABURI, Senior Researcher
Hiroumi SHINA, Senior Researcher
Yuji WADA, Group Leader- Research Institute of Science fir Safety and Sustainability, National Institute of Advanced Industrial Science andTechnology. (AIST)
Kenji MATSUDA, Senior Manager of Engineering Department
Kazuhiro HASEGAWA, Section Manager of Engineering Department- The Japan Refrigeration and Air Conditioning Industry Association. (JRAIA)
Kenji TAKAICHI, Staff Engineer- The Japan Refrigeration and Air Conditioning Industry Association. (JRAIA)(Appliances Company Corporation Engineering Division, Panasonic Corporation.)
Ryuzaburo YAJIMA- The Japan Refrigeration and Air Conditioning Industry Association. (JRAIA)(Daikin Industries, Ltd.)
Kenji UEDA
- The Japan Refrigeration and Air Conditioning Industry Association. (JRAIA)(Machinery, Equipment & Infrastructure Air-Conditioning & Refrigeration Division Chiller & Heat Pump
Engineering Department, Mitsubishi Heavy Industries, Ltd.)131

Takeshi ICHINOSE, Group Leader- Business Affairs Department, Japan Automobile Manufacturers Association, Inc. (JAMA)
Atsushi OOKI, Group Manager- Japan Automobile Manufacturers Association, Inc. (JAMA)(Toyota Motor Corporation.)
Tetsuya SUZUKI, Researcher- Japan Automobile Manufacturers Association, Inc. (JAMA)(Japan Automobile Research Institute.)
Jun ICHIOKA- Safety Committee, Japan Society of Refrigeration and Air Conditioning Engineers. (JSRAE)(Toyo Engineering Works, Ltd.)
Kenji TSUJI- Safety Committee, Japan Society of Refrigeration and Air Conditioning Engineers. (JSRAE)(Daikin Industries, Ltd.)

Observers
Shinichi OIKAWA, Senior Analyst
Shinzo KATAGIRI, Deputy Director
Yoichi MIYASHITA, Technical Specialist- Fluoride Gases Management Office, Chemical Management Policy Division, Ministry of Economy, Trade andIndustry
Shinji KAKUNO, Deputy Director General
Masayoshi TAKANO, Director
Masamichi ABE, Project Coordinator- Environment Department, New Energy and Industrial Technology Development Organization. (NEDO)
Moriaki IINUMA, Manager- Refrigeration Safety Division, High Pressure Gas Safety Department, The High Pressure Gas Safety Institute ofJapan
Yasuhisa NAKASO, Manager (Energy Utilization Research)- Sales Department, The Kansai Electric Power Co, Inc.
Hiroaki OKAMOTO, Project Researcher
Makoto ITO, Student- Graduate School of Frontier Sciences, The University of Tokyo.

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