Reference No.
Name of the accident:
2012-106
Explosion and fire at a resorcinol plant
Date and time of occurrence:
Place of the accident:
2:15 am on April 22, 2012
Waki-cho, Kuga-gun, Yamaguchi Prefecture, Japan
Plant name:
name:
Resorcinol plant

Equipment name:
name:
Oxidation reactor

Contents:
Contents:
Dihydroxy peroxide (DHP)

Main structural material:
Summary of dimensions(mm)material:
dimensions(mm):(mm):JIS SUS304L / JIS SM490B Inner diameter 5,150
clad
TL 12,000
Normal operating
Normal operating
operatingoperatingCapacity to producepressure::temperature::pressuretemperature
Highigh-pressure gas:
gas:
-5℃
1.96MPa
25,600m3(Normal)/day

Damage situation:
situation: （Photo 1）
A problem arose with the steam generating plant and all plants the steam was supplied to were being put
through emergency shutdowns one by one when the dihydroxy peroxide (DHP) inside the oxidation reactor inthe resorcinol plant (Fig. 1) decomposed. The temperature and pressure inside the oxidation reactor rose
rapidly and the oxidation reactor burst (Figs. 2, 3), causing an explosion and fire. There was a second
explosion at the same reactor. One employee who was working near the oxidation reactor at the time of thefirst explosion was killed, and 25 people including local residents were injured. Additionally, 999 buildings
and homes in the surrounding areas were damaged. (Fig. 4, 5) (Based on final report from the company)
Overview of the accident:<Timeline after the accident>
1. At 2:15 am on April 22, an explosion and fire occurred at the resorcinol plant.
2. At 2:20 am, the fire department was notified, three local headquarters were established (Command HQ,Response HQ and Administrative HQ), and firefighting activities were started.
3. At 8:05 am, a second explosion occurred at the resorcinol plant.
4. At 5:15 pm, the Iwakuni District Fire Union Fire Department declared that the fire was under control.
5. At 2:31 pm on April 23, the Iwakuni District Fire Union Fire Department declared that the fire wasextinguished.
<Situation of the explosion>
1. At the resorcinol plant, raw material m-diisopropylbenzene (m-DIPB) is oxidized in the oxidation reactorwith oxygen in the air to create the resorcinol intermediate, dihydroxy peroxide (DHP). (Material-1)
2. Nitrogen was introduced into the oxidation reactor to maintain replacement from air and liquidagitation, and the cooling water was switched from circulating cooling water to emergency cooling water.
3. The internal temperature of the oxidation reactor slowly began to drop, but later, the operator decided
that the cooling speed was too slow.
4. So he released the interlock triggered by the emergency shutdown, and changed the cooling method tocirculation cooling water which is normally used once the reaction is complete. This stopped the flow ofnitrogen that was being used to keep the liquid agitated. At this point, the operator did not notice thatthe liquid agitation had stopped.
5. Cooling coils are installed in the bottom half of the oxidation reactor so the bottom half was being cooled,
but since the nitrogen was stopped and so liquid agitation was also stopped, the DHP in the upper partof the reactor without the cooling coils began to decompose and generate heat.
6. The operations and situations leading up to the explosion are explained in Fig. 6 , but it was confirmedthat when the temperature increases in adiabatic conditions, self-heating of DHP becomes significant,which causes a rapid rise in both pressure and temperature.
7. Through reaction analysis, it is assumed that the process in which the decomposition of DHP starts
when radicals are generated, the heating reaction process involving peroxy radicals, and the generation
Copyright © The High Pressure Gas Safety Institute of Japan1

of gases due to these two processes generated pressure that exceeds the burst pressure and resulted therupture. (Material-2)
8. It is understood that, after the rupture of the oxidation reactor, the DHP and the decomposed gases
mainly consisting of methane were dispersed, diffused, ignited and caused the explosion and fire.
9. The ignition source was not identified but it is likely to be one or more of the following: thecollision/friction between metals caused by the rupture of the oxidation reactor, the discharge of static
electricity charged when the liquid burst out of the oxidation reactor, the electric sparks caused by shortcircuits of electrical cables and electric apparatus after the rupture, or the temperature elevation of theDHP exceeding the ignition temperatures.
Causes of the accident:
accident:
1. There was insufficient capability for cooling the oxidation reactor in the event of an emergency
shutdown.
2. Conditions for releasing the interlock were not clearly defined.
3. The thermometer for the interlock was set only in the lower part of the oxidation reactor and not in theupper part.
4. It was not easy to notice abnormalities during emergency shutdown just by looking at the DCS screen(Did not show nitrogen flow rate, temperature distribution in the oxidation reactor, and relationshipbetween positions of the thermometers and the indicated temperatures) and the alarms were notappropriate (Not triggered when gas for agitation is stopped).
5. Concerning the interlock, education materials were inadequate (the fact that nitrogen is stopped when
the interlock is released was not described on them, the operator did not understand the importance ofagitation) and training was not sufficient.
6. The procedure in the event of an emergency shutdown of the oxidation reactor was not sufficiently
defined, and risk assessments of the equipment in cases when the nitrogen supply is stopped were notconducted.
Measures to prevent recurrence:
recurrence:
1. Ensure the necessary capability for cooling the oxidation reactor in the event of an emergency shutdown.
2. Clarify the conditions in which the interlock may be released.
3. Install thermometers at multiple points in the oxidation reactor.
4. Create DCS screen and review alarms to ensure operators can easily notice abnormalities during
emergency shutdown.
5. Prepare educational materials and conduct training regarding interlocks.
6. Review the operation procedure in the event of an emergency shutdown of the oxidation reactor andreview equipment risks.
Learned lessons
lessons:essons:
1. Insufficient risk assessment.
2. Insufficient passing down of skills (Communicate information regarding safety from the design staff tothe operators, make efforts to continue passing down skills).
3. Disregarding regulations and rules (Insufficient compliance and review).
4. Decline in onsite safety management capability (Overconfident that safety has been secured).
5. Lack of ownership regarding safety/hazards (Lack of alertness and sense of crisis).
Remarks:
Remarks:
1.

2.

They established a "Fundamental Safety Review Committee" chaired by the company president and are
currently promoting "efforts for fundamental safety" company-wide. They held a progress report meeting inOctober 2013, and they are continuing their efforts in safety.
They held a total of 8 meetings of the Accident Investigation Committee with the participation of experts.

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 Japan2

Related figures and material

Photo 1 View of accident site

Fig.1 Position of the resorcinol plant and damage to equipment and pipes

Fig.2 Specifications of the oxidation reactor

Fig. 3 Image of the scatteringof the oxidation reactor

Copyright © The High Pressure Gas Safety Institute of Japan3

Fig. 5 Damage outside plant premises

Fig. 4 Scattering of large debris from theoxidation reactor

Reaction routeBatch

slow (96℃(96℃）

fast (96℃(96℃））

・OH・CH3

ContinuousOH
Cleavage

Reoxidation

Refining

Heatgeneration

OHm-DIPB(2) Heat reaction process

KetoneKetoneDHP
DHP
RadicaltypeOxidation

Process(1) Decomposition
start process

Oxyradical
Oxyradical

H2O, CH4, HHP
OOH

RSConditions

Reaction formula

Explanation℃
Oxidation Temperature: 96℃
Pressure: 520kPa
Reaction time:
Approx. 40hr
Batch reaction

OH

OOH

O2

O2＋OOHm-DIPB

MHP

OOH

OOH

DHP

HHP

m-DIPB is oxidized
with air to obtain
DHP. HHP is also
obtained as a byproduct.

O2
PeroxyPeroxy radical
radicalOOH

Heatgeneration

Slight heatgeneration

OO

Tetraoxide
Tetraoxide

Dimer
Dimer peroxideperoxide

Pressures gases
variouPressure increased
increased inin thethe systemsystem due
due toto thethe generation
generation ofof various
variousgases (O(O22,,CHCH44,, HH22O)O) andand thethe rise
rise inin temperature.
temperature.
*The three types of radicals are highly reactive, so they mostly disappear after reacting with DHP.

Material-1 Resorcinol plant block flow andreaction formula

Material-2 DHP decomposition reaction
mechanism

Fig. 6 Operation condition up to the explosion and fire and temperature and pressure trends

Copyright © The High Pressure Gas Safety Institute of Japan4