EH-89-1 Ventilation Ducts - An Underrated Fire Hazard
ENVIRONMENT, SAFETY & HEALTH
BULLETIN
Assistant Secretary for U.S. Department of Energy
Environment, Safety, & Health Washington, D.C. 20585
DOE/EH-0087 Issue No. 89-1 May 1989
Ventilation Ducts - An Underrated Fire Hazard
May 11, 1989, marked the 20th anniversary of the Rocky Flats (Colorado) fire.
This fire, which occurred in Building 776-777 of the facility, spread very
rapidly through the overhead conveyer lines and one of the interconnecting
conveyors into the center line. Damage to Building 776-777 and its equipment
was extensive. Not only was there fire and smoke damage, there was also
severe damage to substantial portions of utility systems within the building
and internal plutonium contamination.
Although the exact cause of the fire was not determined, evidence indicated
that the long, uninterrupted glove box lines in Building 776-777 created a
wind-tunnel effect. In addition, the interconnected conveyor system, which
had no physical barriers, provided a path for the fire to spread rapidly over
a long distance. The plastic windows that were a major structural part of the
containment system created an additional fuel source in the glove box
containment system; continuous operation of the glove box ventilation system
provided a constant supply of air to support combustion. Thus, the 1969 fire
at Rocky Flats moved very rapidly over a long distance and caused extensive
damage to the facility.
Duct fires also have the potential to cause extensive damage, since these
fires can easily spread very quickly to other rooms or floors. On April 5,
1989, for example, there was a fire in an exhaust duct for a grinding
operation in Building 444 at Rocky Flats. Like the long, uninterrupted glove
box lines that contributed to rapid spreading of the 1969 Rocky Flats fire,
the long, uninterrupted duct enclosures in Building 444 allowed the fire to
spread very quickly.
Common Duct Fire Elements - Inadequate Inspection, Cleaning, Monitoring, and
Control
The duct fires described above are only two of a significant number that have
occurred over the past 10 years. All of these fires had two elements in
common: (1) lack of an adequate duct inspection and cleaning program; and (2)
lack of adequate monitoring and control of "hot work" activities, such as
cutting, welding, and grinding.
In a duct fire at the Martin Marietta facility in Oak Ridge on April 19, 1989,
oil residue was ignited by a piece of hot oxide that entered the exhaust
duct. Although periodic cleaning had been recommended following a similar
incident at the facility in 1979, the exhaust system obviously had not been
cleaned. The buildup of oil and oxide residue found in the exhaust system
ductwork apparently had accumulated over a period of years.
DOE 5380.4 designates National Fire Protection Association (NFPA) standards as
the "prescribed standards" for fire protection programs at DOE facilities. Two
of these standards, NFPA 90A (Standard for the Installation of Air
Conditioning and Ventilation Systems) and NFPA 91 (Standard for the
Installation of Blower and Exhaust Systems), contain valuable guidance for
inspecting, cleaning, and maintaining these systems. Adherence to these NFPA
standards and the use of an aggressive "hotwork" permit system that required
both a walk-down of an affected area and a dedicated fire watch could have
prevented all of the duct fires reviewed.
High-Risk Operations
In general, the duct fires reviewed could be attributed to one of four types
of operations - torch welding or cutting on plenums; welding, cutting, or
grinding in the vicinity of ducts; grinding sparks igniting loaded filter
bags; or uranium machining.
Torch Welding or Cutting on Plenums - Several duct fires occurred during
welding or cutting operations. These operations typically involved the
modification or demolition of ducts without considering or accounting for any
combustible materials inside them. Fires resulted from the combustion of such
overlooked materials as paper trash (eg., paper towels) and organic fibers
(eg., lint, hair) or from oils that had condensed on the interior duct walls.
There was no indication that a viable inspection or cleaning program for duct
interiors had been implemented in any of the cases reviewed.
Welding, Cutting, or Grinding in the Vicinity of Ducts - Duct fires were also
started due to welding, cutting, or grinding on or near plenums. In these
cases, the fires involved the exterior of the ducts rather than the interior.
The most significant fires in this category were caused by combustion of
either the duct insulation itself or the highly combustible facing that is
found on the insulation of many ducts. Apparently these combustible finishes
were not identified as combustible materials or were not recognized as such
during preplanning activities.
Grinding Sparks Igniting Loaded Filter Bags - In some of the fires reviewed,
combustible materials were ignited during otherwise routine grinding
operations. In one case, a fire occurred because the ventilation system was
loaded with sawdust from a belt sander used exclusively for sanding wood. In
this case, as in all the cases reviewed in this category, there was no
effective duct/filter cleaning program at the facility.
Uranium Machining - Numerous duct fires occurred during uranium machining
operations. Typically, sparks were ingested into the exhaust duct, where they
ignited uranium dust or fines that had collected inside the duct. In some of
these cases, rubberized, flexible sections of duct were also ignited. The
lack of a rigorous duct cleaning program also contributed to these fires.
Recommendations
Taking actions such as those recommended below will help prevent ventilation
duct fires.
1. Site preventive maintenance programs should provide for inspection and
cleaning of ventilation and exhaust ducts. The following areas are of
particular concern:
o Areas where combustible liquids (eg., lubricants or cutting oils,
solvents, etc.) are used. These materials condense on interior duct
surfaces and present a highly combustible interior finish. Lint,
hair, and similar items build up on oily surfaces. Preventive
maintenance is particularly important for ducts serving equipment
where oil is used - in cutting operations, for example. However, it
is important to note that even water-based cutting/cooling fluids can
present a fire hazard. These fluids can condense on the interior
duct surfaces, leaving an oil or ester coating when the water
evaporates.
o Areas where Class "A" combustible materials or fibers may be
entrained in the ventilation/ exhaust system. Laundry and computer
operations, for example, are problem areas for the entrainment of
Class "A" combustibles.
2. To the extent possible, combustible materials should not be used in the
construction and insulation of ducts. Combustible materials used in
these activities include such seemingly minor components as rubberized,
flexible sections of ducts and the paper/foil surface on some insulation.
3. Preplanning activities should be required prior to cutting, welding,
grinding, and other "hot work." These activities include both a review
of the work to be accomplished and an inspection of the actual work area
by a qualified person. Consideration should be given to conductive
transmission of heat to combustible materials or surfaces and to contact
with flame, slag, or sparks. Fire watches should be used at appropriate
locations, and "first-aid" fire fighting equipment should be provided.
(In one of the incidents reviewed, a fire watch was in effect when the
fire began; however, no fire extinguisher was available to extinguish the
fire when it was in the incipient stage.)
4. Sprinkler protection should be installed inside ducts that convey
flammable or combustible materials or in ducts where these materials may
accumulate. If the general area is already protected by automatic
sprinklers, it is often relatively simple to extend protection to the
inside of the duct. (In some of the cases reviewed, sprinkler protection
inside the duct prevented a large fire loss.)
In addition to the recommendations listed above, NFPA 90A and NFPA 91 contain
important and helpful guidance for addressing ventilation duct fires. In
high-risk areas, for example, these standards recommend the installation of an
access door in ducts to facilitate inspection and cleaning. Using these
standards as a basis for developing necessary procedures and programs will
also aid in the prevention of ventilation duct fires.
Conclusion
In the 20 years since the fire in Building 776-777 at Rocky Flats, fire
protection programs have been enhanced at all DOE facilities based on the
recommendations of the Factory Insurance Association and Factory Mutual
Research Corporation. However, in the past 10 years, duct ventilation fires
have resulted in significant losses, and most of these fires had the potential
to cause a much larger loss. More importantly, all of these fires could have
been prevented if the appropriate NFPA standards and the recommendations
listed above had been implemented at the facilities where these fires
occurred.
-----------------------------------------------------------------------------
Bulletin is published so that DOE, program managers and contractors can share
information about potential occupational safety problems relevant to DOE
operations. For more information or additional copies, contact Catherine
Brown, Office of Safety Compliance, Assistant Secretary for Environment,
Safety & Health, U.S. Department of Energy, Washington, DC 20545; telephone
FTS 233-6096, Commercial (301) 353-6096.
----------------------------------------------------------------------------