Reference No.
-Name of the Accident;Accident;
Explosion and fire at an acrylic acid production facility.
Place of the accident:
Himeji-city, Hyogo Prefecture, JAPAN

Date and time of occurrence:
Around 14:35 on September 29, 2012
Plant name:name:
Acrylic acidproduction
facility

Equipment name:
name:
Intermediate tank
(V-3138)

Main structural materials
materials:
Side plate: JIS SUS304 (t 3mm)
Bottom plate: JIS SUS316 (t 4mm)

Summary of dimensions:dimensions:
Inner diameter 4.2m
Height 5.6m
(Thermal insulation installed)
Normal operating
temperature:
Not definedContents:
Nominal capacity:
Normal operating
capacity:
Acrylic acid,pressure:
70m3
Inhibitors, etc.
Atmospheric pressure
Damage situation:
situation:
An intermediate tank (V-3138, Fig. 1) temporarily stored the bottom liquid of the glacial acrylic acid rectifying
column in the acrylic acid production facility ruptured and exploded causing a fire in the surrounding area,
which damaged an adjacent acrylic acid tank, a toluene tank, racks, piping, etc.(Fig. 2)
In this accident, 1 person (a fire fighter) was killed, 5 were severely injured (2 fire fighters, 3 employees), 13
were moderately injured (8 fire fighters, 1 police officer, 4 employees), 18 were slightly injured (14 fire fighters,
1 police officer, 3 employees), for a total of 37 people who were killed or injured.
Overview of the Accident:
Sep. 18 to 20
Total power shutdown in the facility for electrical and instrumentation maintenance work
(total power shutdown work).
Sep. 20
Approx. 21:00 After completion of the total power shutdown work, the intermediate tank (V-3138) wasre-commissioned.
Sep. 21
Approx. 11:00 Liquid was fed into the recovery column (T-6701) from the intermediate tank (V-3138) andT-6701 operation was started. Then, the operation of rectifying column (T-6108) was started
to 14:00
and the bottom liquid of the column T-6108 was directly fed into T-6701.
Sep. 24
Approx. 10:00 The rectifying column (T-5108) operation was started.
Approx. 14:10 Discharging of the bottom liquid of T-5108 was started by feeding to T-6701 via V-3138
Sep. 25
Approx. 9:30
Liquid level built up in the intermediate tank （V-3138）was started by stopped feeding toT-6701 from V-3138.
Sep. 28
Approx. 14:00 After the liquid volume in the intermediate tank （V-3138）reached 60m3, feeding to V-3138
was stopped by switching T-5108 bottom liquid to T-6701 directly.
Sep. 29
Approx. 13:17 The liquid level gauge of the intermediate tank (V-3138) triggered a ‘liquid level high alarm’.
Approx. 13:20
Approx. 13:25
Approx. 13:40

Approx. 13:48
to 13:49
Approx. 14:00
Approx. 14:02
Approx. 14:35
22:36
Sep. 30
15:30

White smoke emitted from the V-3138 vent was observed.
The operators started spraying water onto V-3138 using private fire hydrant.
The operation shift leader made the plant-wide announcement and alerted the company
disaster prevention team. The V-3138 liquid level gauge reading exceeded the instrument
indication limit value (84.8 m3).
Member of the disaster prevention section notified the situation to the fire station throughthe hot line.
The company disaster prevention team started spraying water onto V-3138.
The public fire brigade arrived at the scene and set a cordon.
The V-3138 liquid level gauge reading dropped drastically and a ‘liquid level low alarm’ wastriggered. V-3138 ruptured and exploded. The contents of V-3138 ignited and resulted in fire.
The fire was brought under control.
The fire was extinguished.
Copyright © The High Pressure Gas Safety Institute of Japan1

[Damage condition of the intermediate tank V-3138]
1. The roof plate broke and separated near the roof-to-shell joint. The roof plate has split into two and being
thrown to a distance of about 50m (see Fig. 3).
2. The shell plate was vertically torn in a near straight line at 270° position and deformed into casement-type
opening and left almost like a flat plate within the dike at the accident site. The bottom plate partly brokenear the shell-to-bottom joint and remained inside the dike.
3. The cracks formed around the outlet nozzle of cooling water coil propagated and split the tank shell plate
vertically in both directions at 270 ﾟ position. The upwards crack broke into the roof plate and ran throughit near the 135 ﾟ position. The roof and bottom plates generally cracked in the circumferential direction
near their joints with the shell plate.
Causes of the accident:
accident:
1. Even though high temperature T-5108 bottom liquid was building up in the intermediate tank (V-3138),
the fact that the circulation of recycle to top was not commissioned has caused acrylic acid to remainstagnant for a significant long period of time at high temperature in the upper portion of the tank (Fig. 4).
2. Dimer formation of acrylic acid accelerated in the tank liquid with high temperature zones and the liquid
temperature in the storage tank was elevated by the heat of dimerization. As a result, the polymerization
reaction of acrylic acid starts to proceed and increased the liquid temperature further.
3. The abnormal condition was not possible to recognize due to the lack of thermometers and inadequate
temperature monitoring, until the polymerization reaction of acrylic acid had proceeded. As a result,V-3138 exploded, followed by fire and caused enormous casualties and property damages (see Figs. 2 and5).
Measures to prevent recurrence:
recurrence:
1. Measures to prevent recurrence for equipment causing the accident(1) To prevent excessive heating in the tank feed liquid, specification of the T-5108 bottom liquid transfer pipeshould be changed.
(2) To control the appropriate temperature of the stored liquid in V-3138, specifications of the intermediatetank (V-3138) and (new) associated equipment should be studied. The criteria and its response procedure
for the abnormal status should be clarified.
(3) To clarify safety of the restored equipment and necessary matters for stable operation, documentation likes
manuals, P&ID should be developed or revised.
(4) To operate the restored equipment safely and stably according to the manuals, education and training
should be provided.
2. Measures for preventing similar accidents(1) To ensure risk assessment is implemented whenever there are changes in non-routine works, procedures,
methods, equipment, etc. and each work details are disseminated, basic rules for safe work management
should be established, rules of Management of Change and practice of operating instructions should bereviewed.
(2) To enhance the emergency response capabilities when abnormal situations occur, crisis management
manual should be developed, company disaster prevention manual should be reviewed and training onthese manuals should be provided.
3. Horizontal deployment of disaster prevention measures
Review the above countermeasures and compare them against the current practices in other businessfacilities.
4. Fostering a safety culture promoting safe plants and enterprises
It should be made aware that safety is not something to be provided by others but rather need to recognize
and achieve safety by themselves, and this concept should be reflected in the future behavior oforganization and individuals.
Learned lessons
lessons:essons:1. The latest data of properties, reactivity and risks of handled chemicals (raw materials, intermediate
products, additives, reactants, etc.) should be checked and reflected on their operational management,safety management and facilities management.
2. Risk assessment in the event of non- routine works, management of change and abnormal situations aswell as risk assessment of facilities and processes should be conducted to enhance safety.
3. It should be confirmed that in facilities such as reactors, storage tanks and intermediate tanks with risksof polymerization reaction, decomposition reaction and runaway reaction in which cooling coil, U-tube or
the like is installed to keep them at constant temperature and control the reaction, safety is secured
Copyright © The High Pressure Gas Safety Institute of Japan2

without causing abnormal reaction due to temperature elevation or impurities on the internal walls when
the stored liquid volume is temporarily increased to above the cooling devices.
4. Operating standards and operation manuals in any abnormal, disaster and emergency situations should
be developed in advance. Safe emergency responses such as stop the reaction or emergency stop should beclearly defined in the event in which it is beyond the scope of such standards or manuals, and they shouldbe thoroughly informed through education and training.
5. Past troubles and abnormalities should be shared not only in the department where they occurred but also
company-wide so that occurrence of similar accidents and recurrence of identical accidents can beprevented. It is important information on accidents and troubles which have occurred in other businessfacilities and departments is shared and used at our own workplace.
6. As a top and leading company, introduction of safety audits and safety assessment by a third party isrecommended in order to achieve continuous safe operation.
7. Safety awareness should be shared from top management to all employees so that continuous stableproduction will not soften safety awareness and not become less sensitive towards danger. The corporate
mission statement and security management policy should be understood and they should be reflected in
the actions of organizations and individuals.
8. In this accident, an atmospheric tank ruptured, exploded and caused major damages due to apolymerization reaction. It is important to thoroughly inform the prevention and safety measures foraccidents resulted in atmospheric tanks as well as rupture and explosion of high-pressure gas reactors,
storage tanks .
9. Information sharing which include critical information of facilities, equipment, chemicals, affected areas,
etc is important between the business facilities and relevant organizations (fire authorities, police,authorities concerned, etc.) which will enter the site in the event of accidents and abnormal situations.
Remarks:
Remarks:
Acrylic acid (CH2=CHCOOH) is a colorless, transparent, flammable liquid with a pungent odor. Due to its
unstable double bond, acrylic acid is readily converted into a dimer (DAA) via dimerization reaction and topolymerize through polymerization reaction.
The DAA forming reaction is not susceptible to the atmosphere and inhibitors. Typically, the atmosphere iscontrolled so that the oxygen concentration may be 5 vol% or more and inhibitors are added for the purpose of
suppressing the polymerization reaction.
Reference;
Nippon Shokubai Co., Ltd. Himeji Plant Explosion and Fire at Acrylic Acid Production Facility Investigation
Report, March 2013, Accident Investigation Committee, Nippon Shokubai Co., Ltd.
Further, matters that weren’t written in previous report were written by KHK after consideration of Accident
Investigation and Analysis Committee in KHK.
Crude Acrylic Acid
Production Facilities

2AA
3AA

Crude
Acrylic Acid

Glacial Acrylic Acid
Production Facilities

T-2108GlacialAcrylic Acid

T-3108GlacialAcrylic Acid

T-4108GlacialAcrylic Acid

T-5108GlacialAcrylic Acid

T-6108GlacialAcrylic Acid

Crude
Acrylic Acid
Waste oil

4AA

5AA

T-2701

T-6701

Crude
Acrylic Acid
Waste oil

Rectifying
ColumnRecovery ColumnV-3138

Intermediate Tank

Fig.1 Configuration of acrylic acid production processes
Copyright © The High Pressure Gas Safety Institute of Japan3

Fig.3 Reconstruction
diagram (sketch) ofV-3138 fragments

Fig.2 Damaged Tank
(View from southwest and zoom in)

Fig.4 Status of tank V-3138 after liquid storing

Location of Damaged Equipment
Location of Scattered Contents
Location of V-3138 Scattered Fragments

Main fire areas
Areas where Fire Spreaded
Location of Casualties
Foam extinguished from public
chemical fire engine
Water Spray from Public Fire Engine
Water Spray from Private Fire Hydrant
Water Spray from Private Fire Hydrant① to ④ Measures taken after the explosion andfire occurred.

Fig.5 Fire areas around the intermediate tank

The High Pressure Gas Safety Institute of Japan (KHK)
Information Service & Research Dept. International Affairs Office
Web: http://www.khk.or.jp/english/index.html Mail : oversea@khk.or.jp

Copyright © The High Pressure Gas Safety Institute of Japan

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