An explosion occurred at a utility boiler, injuring three personnel who were attempting to restart it. The investigation found they had used an unauthorized temporary bypass method for lighting the boiler that involved opening bypass valves without first closing block valves downstream, allowing LPG to enter the furnace. Non-compliance with safety procedures on management of change and control of equipment defects contributed to the accident. Lessons included following safe operating procedures, obtaining authorization for changes, and ensuring all personnel are properly trained.

1. CASE STUDY
ON BOILER ACCIDENT
CHIA BAK KHIANG
ASST. EXECUTIVE ENGINEER
OSD, MOM

2. 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.

3. OVERVIEW OF UTILITY BOILER

4. OVERVIEW OF BOILER
CONTROL SYSTEM
Boiler Control System
Control the
operation of
valves and
actuators
Monitor critical
control
functions for
safe operation of
boiler

5. Status of valves during normal light up

6. INTRODUCTION
On 9 Dec 2000, at about 2:30am, 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

7. PHOTOGRAPHS OF BOILER
AFTER EXPLOSION

8. PHOTOGRAPHS OF BOILER
AFTER EXPLOSION

9. PHOTOGRAPHS OF BOILER
AFTER EXPLOSION

10. PHOTOGRAPHS OF BOILER
AFTER EXPLOSION

11. PHOTOGRAPHS OF BOILER
AFTER EXPLOSION

12. 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 12:30am. They made
several attempts but were unsuccessful.
At 2:20am, 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.

13. 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.

14. 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

15. 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.

16. 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.

17. 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.

18. 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.

19. Status of valves after accident

20. Fuel Flow Line after accident
1st Trip valve
100% closed
1st bypass valve
50% open
2nd bypass valve
50% open 2nd Trip valve
100% close
Control valve
66% open
Block valve
100% open
Block valve
100% open
Block valve
100% open

21. 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.

22. CONCLUSION
LPG
FIRE
TRIANGLE
Air (Oxygen)
Hot Furnace Wall

23. 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.

24. 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.

25. THANK YOU
Don't Neglect Your Boilers Operation
Just Because They Operate
Automatically