CASE STUDY ON BOILER ACCIDENT

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CASE STUDY ON BOILER ACCIDENT
CHIA BAK KHIANG ASST. EXECUTIVE ENGINEER OSD, MOM
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OVERVIEW OF UTILITY BOILERS
The boiler involved in the accident was a water
tube unit with attached economiser and
superheater. Total heating surface is 2203 sq.m
and its design pressure is about 12 000 KPa and
it can produce 160,000 kg/hr of steam. The
burner system can burn 8 different types of fuel
using various nozzles. The boiler is protected
from overpressure by 2 PSVs at the steam drum and
1 PSV at the superheater.
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OVERVIEW OF UTILITY BOILER
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OVERVIEW OF BOILER CONTROL SYSTEM
Boiler Control System
Control the operation of valves and actuators
Monitor critical control functions for safe
operation of boiler
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Status of valves during normal light up
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INTRODUCTION

• On 9 Dec 2000, at about 230am, three personnel
  were trying to re-start the boiler when an
  explosion occurred inside the furnace of the
  boiler.
• The three personnel were badly injured with more
  than 50 2nd degree burns on their bodies.
• Two of them subsequently passed away later in the
  hospital
• Deceased 1 - Technician/ Male / 23 yrs old
• Deceased 2 - Technician/ Female / 21 yrs old

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PHOTOGRAPHS OF BOILER AFTER EXPLOSION
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PHOTOGRAPHS OF BOILER AFTER EXPLOSION
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PHOTOGRAPHS OF BOILER AFTER EXPLOSION
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PHOTOGRAPHS OF BOILER AFTER EXPLOSION
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PHOTOGRAPHS OF BOILER AFTER EXPLOSION
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DESCRIPTION OF ACCIDENT
Boiler was on LPG firing. Night Order was given
to light up diesel burner in Boiler. The three
personnel attempted to light up the diesel burner
at about 1230am. They made several attempts but
were unsuccessful. At 220am, they attempted to
light up the diesel burner. However, the boiler
experienced a master fuel trip which shut down
the boiler totally. While restarting the boiler
on LPG, an explosion occurred.
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OBSERVATIONS FINDINGS
The boilers were in the commissioning stage at
the time of the accident. Written operational
procedures were available for cold and hot
start-up of the boilers Investigations revealed
that the startup team encountered some
difficulties in lighting the boiler with LPG some
time back. To overcome the problem, they devised
a temporary manual bypass method. This bypass
method was not the same as the operational
procedures.
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OBSERVATIONS FINDINGS
The bypass method was used by the startup team as
a temporary measure and they had stopped using it
when a permanent solution was found to overcome
the problem. This method was only to be used by
the startup team and no process technicians were
instructed to use it. Investigations revealed
that process technicians were present working on
this method with the startup team when it was
used. This method had been used on several
occasions by most of the process technicians
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OBSERVATIONS FINDINGS

• Company Internal Safety Management System
• Investigations revealed that the S.M.S. was not
  effectively implemented in the plant prior to the
  accident
• There was no Management of Change approval put
  up for management approval to use the temporary
  bypass method.
• The bypass method required the opening of 2
  bypass valves. There was no Control of Defeat.
  procedures put up to the management for approval
  to remove the sealed wire on these valves.

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OBSERVATIONS FINDINGS

• Company Internal Safety Management System
• Pre-Startup Safety Review (PSSR) was claimed to
  be carried out on the Boiler. But the PSSR
  document was not available for our review during
  the investigation.
• It was found that the bypass valves did not have
  any sealed wire when the startup team first
  implemented the bypass method. However, the team
  did not find out further why there was no sealed
  wire on these valves.

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OBSERVATIONS FINDINGS
Training Experience All technicians were given
8 months of orientation and training programme.
This included technical and S.M.S. training. The
2 deceased were Process Technicians but were not
certified boiler attendants. The injured was a
Supervisor and a certified 1st Class Steam Boiler
Attendant. The injured claimed that he was
unaware of the bypass method and that it was
being used on 9 Dec. He also felt that the
training provided was insufficient for him to
operate the boiler.
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SITE FINDINGS

• Site investigations after the accident confirmed
  that the 2 bypass valves were 50 open. This
  confirmed that the bypass method was utilised to
  restart the boiler.
• Data records confirmed that the LPG control
  valve was about 66 open just before the
  explosion.
• The block valves before and after the control
  valve were fully open.
• A direct path was therefore established to allow
  LPG to enter the firebox, resulting in the
  explosion of the boiler.

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Status of valves after accident
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Fuel Flow Line after accident
2nd bypass valve 50 open
1st bypass valve 50 open
2nd Trip valve 100 close
1st Trip valve 100 closed
Control valve 66 open
Block valve 100 open
Block valve 100 open
Block valve 100 open
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CAUSE OF ACCIDENT

• Use of temporary bypass method to restart the
  boiler after it had tripped.
• Two bypass valves of the trip valves were opened
  without first closing the two block valves,
  downstream of the LPG control valve
• Non-compliance of the company internal S.M.S.s
  safety requirements
• - The use of unauthorised temporary bypass
  method
• - The removal of sealed wire on the bypass
  valves.

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CONCLUSION
LPG
Air (Oxygen)
FIRE TRIANGLE
Hot Furnace Wall
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LESSONS LEARNT

• All personnel who are operating boiler must
  follow Safe Operating Procedures.
• Authorisation must be obtained before
  introducing change to the boiler system or
  procedures.
• Ensure all personnel who are operating boiler
  received adequate training and supervision.
• Ensure proper documentation.

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ACTIONS TAKEN
The company had been instructed to carry out a
thorough inspection and examination on the
remaining Boiler and carry out necessary
rectification works to restore the boiler to safe
operating condition. The company had also
thoroughly reviewed the BMS and carried out
rectification to improve the system. They had
also reviewed and audited their internal S.M.S.
to identify weaknesses and to close such gaps.
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THANK YOU
Don't Neglect Your Boilers Operation Just Because
They Operate Automatically