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| Technical Information Bulletin |
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U.S. Department of Labor
Occupational Safety and Health Administration |
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Potential for Natural Gas and Coal Dust Explosions in
Electrical Power Generating Facilities
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| TIB 01-11-06 |
This TIB is not a new standard or regulation,
and it creates no new legal obligations. It is
advisory in nature, informational in content,
and is intended to assist employers in providing
a safe and healthful workplace.
For a more detailed description of the nature
and effect of Technical Information Bulletins,
see the Important Information box at the end of
this bulletin. |
Purpose
The purpose of this Technical Information Bulletin
is:
- to remind employers who operate electrical power generation facilities about
potential explosion hazards during boiler start up, operation, and shutdown;
- to provide guidance to the Occupational Safety and Health Administration (OSHA),
and State Plan Compliance Safety and Health Officers regarding prudent
practices established by the National Fire Protection Association (NFPA) and
the American Society of Mechanical Engineers (ASME) for the safe operation of
boilers and furnaces in electrical power generating facilities; and
- to provide guidance to safety professionals who serve the power generation
industry including consultants, insurance auditors, and others who provide
services and equipment to the industry.
Background
The State of Michigan is one of 23 States that have chosen to retain authority
for occupational safety and health law enforcement under a State Plan
approved by OSHA. Therefore, the General Industry Safety Division (MIOSHA),
under the Bureau of Safety and Regulation (BSR), Michigan Department of Consumer
and Industry Services (CIS), investigated a power plant explosion in 1999 that
resulted in 6 fatalities and 14 serious injuries. The primary explosion resulted
from an unintentional natural gas buildup in the furnace of an idle power boiler
and was followed by a secondary explosion of disturbed coal dust. MIOSHA found
coal dust accumulations throughout the powerhouse on ledges, structures, and
equipment. This boiler was fired with natural gas, coal, and blast furnace gas
to produce steam to power the turbines.
Jurisdictional Issues
Both MIOSHA and the Boiler Division of the Michigan Bureau of Construction Codes
responded following the explosion. The Boiler Division had limited jurisdiction
and could investigate only the wet-side of the boiler (i.e., the pressure vessel
in which the steam is generated). MIOSHA had jurisdiction over all other aspects
of the matter including compliance with MIOSHA regulations -- e.g., R408.18602
(adopting the Federal OSHA standard, 29 CFR 1910.269 on Power Generation), and
R408.18502 (adopting the Federal OSHA Standard, 29 CFR 1910.147 on Lockout/Tagout);
R408.1011 (a), MIOSHA's analogue to Federal OSHA's General Duty Clause, Section
5 (a)(1) of the OSHAct (P.L. 91 - 596 December 29, 1970, and its amendments).
Incident Description
Based on interviews and observations, and after reviewing relevant
documentation, the investigators developed a chronology of events leading to the
explosion. Employees were raking the boiler offline in preparation for its
annual licensing inspection. Prior to the time of the explosion, blast gas and
pulverized coal systems were eliminated as fuel sources, and maintenance
personnel were blanking the two main 10-inch natural gas lines.
Power Service Operators (PSO's) were required to shut up the 30 natural gas
valves, including pilots, ignitors, and burners located on two different floors.
Maintenance personnel blanked, disconnected, and/or capped 6 of the 30 natural
gas lines and valves. PSOs monitored induced draft, forced draft, primary fans,
steam pressure, temperature, and water levels during the shut down. During this
process, PSOs failed to close one of the two 10 inch main natural gas shutoff
valves feeding the burners. As a result, natural gas was trapped between shutoff
valves and burner control valves, and the burner control valve subsequently was
reopened to vent the trapped gas into the furnace box. This allowed the natural
gas at line pressure to flow into the furnace box for approximately 2 minutes.
The primary explosion occurred when this gas encountered ignition sources, such
as hot or smoldering ask in the superheater or generating tubes, or possibly a
spark from the electrostatic precipitator. A secondary explosion resulted from
disturbed coal dust dispersed during the initial explosion.
Investigation Findings
The investigators identified the following engineering control and work practice
deficiencies, which were cited under the Power Generation and the Lockout/Tagout
Standards, as well as the General Duty Clause:
- Lack of adequate combustion controls: Inoperative flame monitor and burner
safety devices.
- Lack of burner/ignitor control system: Inoperative pilot ignitors. Pilots
were lit with a glove soaked in alcohol.
- Purging of natural gas into an idle furnace: The natural gas valve train
not equipped with a double block and bleed to atmosphere.
- Lack of proper identification of isolation valves, butterfly valves, pilot
valves, and ignitor valves: Valves were improperly marked or identified, and
improperly located for boiler shutdown and startup operations.
- Failure to establish proper written procedures for startup/shutdown of
boilers: Written procedures are necessary due to personnel changes
associated with shift assignments, the complexity of boiler shutdown, and
the infrequency of shutdowns.
- Failure to control accumulations of appreciable coal dust: Poor
housekeeping allowed coal dust to accumulate throughout the facility (e.g.,
on floors, ledges, structures, beams and equipment).
- Failure to institute proper lockout procedures specific to boilers: No
specific procedures for boilers or for release from lockout; lockout devices
were not identified during blanking operations.
- Failure to conduct adequate/effective job briefings: Employee briefings
were not conducted prior to the boiler shutdown. Briefings would have
revealed that two employees had not performed this task within the last year
and that employees needed to be retrained.
- Failure to provide adequate training, procedures, and certifications of
proficiency for employees assigned to boiler operations.
The investigators also found that individual departments within the
powerhouse handled safety-related issues. This produced a situation where safety
issues potentially went unrecognized and where information regarding safety was
not necessarily shared with the appropriate personnel. For example, insurance
audits and engineering studies recommending modifications to combustion/safety
controls were viewed as operational issues without consideration for, or input
from, the safety department.
Recommendations
The investigators concluded that this accident may have been prevented if
industry standards such as those identified below, had been followed:
- NFPA 8502, "Standard for the Prevention of Furnace
Explosions/Implosions in Multiple Burner Boilers;"
- NFPA 8503, "Standard for Pulverized Fuel Systems;"
- ASME, BPVC Section VII, "Recommended Guidelines for the Care of Power
Boilers;" and
- ASME B31.1, "Power Piping."
NFPA Standard 85B, "Standard for Prevention of Furnace Explosions in
Natural Gas-Fired Multiple Burner Boiler-Furnaces," which was an earlier
version of NFPA 8502, Section 2-1.3(b), identified "fuel leakage into an
idle furnace and the ignition of the accumulation by a spark or other source of
ignition" as one of the most common explosive conditions in connection with
the operation of a boiler-furnace. Based on the evidence in the case file for
this investigation, the MIOSHA/OSHA investigative team recommends that:
- When boilers are manually operated in lieu of automated combustion/safety
controls, additional emphasis must be placed on work practices. Necessary
elements for emphasis include written operating procedures, job briefings,
verification checklists, training, proficiency testing, and maintenance of
training records.
- When equipment nears the end of its useful life, the employer must be
particularly diligent, as well as vigilant, with respect to maintenance.
Boiler safety controls (e.g., flame monitors) must be operational and well
maintained.
- Coal dust accumulations must be recognized as a serious hazard and
housekeeping must be performed with diligence to control and/or limit coal
dust accumulations.
- To ensure safety there must be clear lines of communication among all
power plant entities, including: the safety department, employee safety and
health representatives, security department, maintenance, operations, and
management. A comprehensive safety committee representing all these
organizational functions is essential.
Important Information on the
Nature and Effect of Technical
Information Bulletins
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OSHA’s Directorate of Science, Technology and Medicine (DSTM) issues Technical Information Bulletins
(TIBs) to provide information about occupational
hazards and /or to provide information about
noteworthy, innovative, or specialized procedures,
practices and research that relate to occupational
safety and health. DSTM selects topics for TIBs
from recognized scientific, industrial hygiene,
labor, industry, engineering, and/or medical
sources.
The Occupational Safety and Health Act
requires employers to comply with hazard-specific
safety and health standards. In addition, employers
must provide their employees with a workplace
free from recognized hazards likely to cause death
or serious physical harm under Section 5(a)(1), the
General Duty Clause of the Act. Employers can be
cited for violating the General Duty Clause if there
is a recognized hazard and they do not take appropriate
steps to prevent or abate the hazard. However,
the failure to implement TIB recommendations
is not, in itself, a violation of the General
Duty Clause. Citations can only be based on
standards, regulations, and the General Duty
Clause.
Further information about this bulletin may
be obtained by contacting OSHA’s Directorate of Science, Technology and Medicince at 202-693-2300 |
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