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10 MYTHS ABOUT INDUSTRIAL FIRE PROTECTION
By Dominique Dieken , PE, CFPS, Senior Engineer, HSB Professional Loss Control,
Crestline, CA -- 6/1/2000
Key concepts
-Misconceptions about fires often come from what we have seen on television or
in movies.
-Many widely held beliefs about fire protection are untrue.
-Properly installed and maintained systems in all areas of a plant can drastically
reduce damage potential.
Most fire protection engineers would agree that there are many misconceptions about
fire damage and suppression equipment. While no amount of fire protection can guarantee
absolute immunity, a careful analysis of hazards, combined with the proper selection
of fire protection systems, can drastically reduce potential damage.
Unfortunately, laymen often misunderstand the recommendations given by fire protection
professionals. And since "unfriendly" fires do not happen to most of us on a regular
basis, we have images of fires seen in movies or on television. In order to offer
the viewer a clear picture, movie directors typically use clean-burning natural
gas flames in the fire scenes, which are unrealistic at best. To accurately portray
most fires, the director would have to show a black screen. Misconceptions like
these often make people confused about fire protection. The following are some of
the most common fire protection-related myths.
Myth 1. Keep sprinklers away from electricity
Electrical fires can produce large quantities of opaque, corrosive, and toxic smoke.
This smoke makes any manual fire fighting efforts-such as using a portable extinguisher-extremely
difficult. Most electrical and electronic equipment exposed to sprinkler water can
be cleaned, rinsed with deionized water, and dried.
Almost always, the fire protection layman opposes the presence of sprinklers in
an electrical room because of "personnel hazard." This argument is weak because
everyone should already have left the room long before a sprinkler actuates. In
most cases, hazards caused by the fire and its products of combustion are much greater
than that of the water discharge or potential for contact with a live circuit. Even
in a case where sprinklers actuate with a person in the room, such as if he was
unconscious, the chances of being harmed by the water discharge are much less than
from the deadly smoke.
Myth 2. Don't use water on flammable liquid/oil fires
While it is true that a straight stream of water when applied to a flammable liquid
fire can actually spread the burning liquid, it is a poor reason to exclude the
use of water at all. Water is an excellent fire suppression agent used to successfully
control and extinguish flammable liquid fires, if properly applied.
Let's take a brief look at the physics of burning liquids. Every flammable/combustible
liquid has a flash point-the temperature at which the liquid gives off a flammable
vapor in sufficient concentration with ambient air to generate an ignitable mixture.
So in reality, it is not actually the liquid that burns, but the vapor.
The proper application of water to a flammable liquid or oil fire has several effects.
1. Water absorbs convective heat above the fire. If it is not absorbed, this heat
can cause structural damage and ignite other nearby combustibles.
2. When applied to structural members, water provides a cooling effect to keep the
materials from failing (for example, structural steel begins to weaken at 800 F).
3. Water extracts heat from the liquid itself, so that when the liquid is cooled
to below its flash point, the fire self-extinguishes.
The method of water application is the key to properly extinguishing a flammable
liquid fire. Trained fire fighters use a spray or fog pattern from their hoses in
order to accomplish the three items discussed above. Fixed sprinkler and waterspray
systems achieve the same effect, but begin suppression earlier, distribute water
more evenly, and cause much less damage than the fire department would, assuming
that they even attempt offensive fire fighting.
Another important aspect of flammable liquid fire control is proper spill containment.
If a pool or "burning" liquid flows outside a sprinkler-protected area, no sprinkler
system will do the job. Therefore, containment must be limited to the areas protected
by the fire suppression system, and for ease of control, the area should be subdivided
into smaller sections.
Myth 3. Sprinklers do more damage than fire
Sprinklers provide early control of a fire, thus providing safety and limiting the
damage. With the exception of the deluge sprinkler/waterspray system (which is only
used for specific high-hazard applications), sprinkler heads only operate when heat
released by a fire melts the fusible link that keeps the sprinkler closed, and the
open sprinklers can be expected directly above the fire seat. Every individual head
must be triggered in that fashion.
Myth 4. Sprinklers may go off accidentally
The failure rates for sprinkler heads are extremely small (on the order of 1 in
16 million or a probability of 6.25×10 -8 ). Inadvertent discharge
of sprinklers is extremely rare and usually attributed to mechanical damage or poor
system design. It is so rare, in fact, that there are not enough data to be more
precise. It is estimated that 1 in 2.5-million installed sprinkler systems will
discharge inadvertently (probability of 4.0×10 -7 ).
To ensure reliability and performance, sprinkler system components, design, and
installation are meticulously controlled by the National Fire Protection Association
(NFPA) standard, NFPA 13, Installation of Sprinkler Systems, the nation's foremost
design and installation standard on the subject. Proper selection and location of
sprinkler heads, and proper system design, minimize the possibility of inadvertent
discharge.
Myth 5. Plants that meet fire and building codes don't need additional
protection
Fire and building codes objectives are to get the occupants out safely before conditions
become hazardous, rather than to protect the building from fire. Since industrial
fires have not historically resulted in extensive loss of life, most building and
fire codes tend to be fairly lenient in industrial facilities. In addition, these
codes usually do not concern themselves with the adequacy of fire suppression systems,
but merely address whether or not their presence is required.
Industrial fire losses do, however, constitute a high percentage of the annual property
losses, a factor that the codes usually do not address. Also, model codes used by
most jurisdictions only contain minimum requirements, even though builders and owners
often look at them as maximum requirements.
If the "codes" don't address property loss prevention, how can you make sure that
your plant is adequately protected? Industrial insurance carriers with a technical
background can offer a wealth of information and support ranging from management
loss prevention programs to special hazard fire suppression protection.
Myth 6. It is better to rely on manual fire suppression
Manual fire fighting efforts are a last resort when attempting to confine and contain
a fire within a plant. By the time the local fire department is notified and arrives
at the scene of a working fire, extensive damage to the building and contents has
already occurred. Add to that the extensive water damage from 1-3/4 or 2-1/2-in.
hose streams (250–500 gpm). In the case of large fires or high-hazard buildings,
the officer in command may decide to take the defensive position of letting the
fire burn itself out and protecting neighboring structures rather than jeopardizing
the safety of firefighters.
Effective fire fighting is much harder than portrayed on television and in movies.
Few people realize that a typical fire extinguisher provides only 10–15 sec of agent
discharge. Unless the fire extinguisher is used in the incipient stage of a fire
and the operator is familiar with the extinguisher's proper use, they are of little
benefit to facility protection. Often, valuable time is wasted emptying fire extinguishers
when the fire department should have been notified immediately.
Using a fire hose can be much harder than it looks. Many 1-1/2-in. "occupant" hoses
are inadequately maintained and could result in injury if used. Smoke quickly impairs
visibility, and products of combustion can turn a room into a deadly trap within
minutes.
For anything other than small, incipient fires, the best thing to do is to leave
the area immediately, notify the fire department from a safe location, and let the
suppression system (if installed) do its job.
Myth 7. Firefighters know fire protection systems
While surveying an industrial plant, the inspector noted that the preaction sprinkler
system valve protecting a fairly large building of wood construction had been turned
off. When questioned, the facility's safety officer replied that he would check
with another employee who was a retired firefighter, which he did promptly. The
retired firefighter informed the safety officer that the impaired sprinkler system
was "legal" because plant personnel were concerned about inadvertent sprinkler discharge
and that someone would open the system valve (located in the fire area) in case
of fire.
This incident reaffirms the misconception that firefighters know all about sprinklers
and other fire suppression systems. Had the retired firefighter been familiar with
the operation of the plant's suppression systems, he would have known that the concerns
were unsubstantiated because preaction sprinkler systems are virtually unsusceptible
to inadvertent discharge and that the valve would not be safely accessible during
a fire.
The fact is that firefighters are trained to deal with fire fighting tactics and
rescue; their training and knowledge on fixed fire protection systems is usually
limited. Fire protection systems are engineered mechanical, electrical, and structural
systems whose evaluation should be left to fire protection engineers and their care
to experienced contractors.
Myth 8. If the plant has sprinklers, it's protected
While sprinklers have an excellent record of protecting people and buildings from
fire, the mere presence of a sprinkler system does not mean that it can adequately
deal with a fire. This point is especially true in facilities with often-changing
hazards.
Sprinkler systems are matched to the occupancy of a building, meaning that the higher
the expected heat release of a fire, the more water a sprinkler system must be able
to deliver. The density, or water flow over a unit area, is a balance between the
available water supply (flow and pressure) and friction resistance of the sprinkler
piping. Engineering calculations are used in the sprinkler system layout and the
pipe selection. Therefore, a sprinkler system that was adequate 10-yr ago may not
necessarily offer adequate protection today.
Myth 9. Halon is toxic and illegal
At this time, no laws or regulatory agencies in the U.S. prohibit the use of Halon
as a fire suppressant. When used as intended as a total flooding or local application
fire suppression agent, no adverse health effects have been reported from the use
of Halon 1301 and 1211 over the past 30 yr. At the typical 5–7% concentration, the
volume of Halon is insufficient to displace a significant percentage of oxygen.
Exposure to Halon at high concentrations only causes temporary adverse health conditions.
Decomposition products of Halon from exposure to flame or surface temperatures over
900 F can be harmful. However, products of combustion from the fire itself (carbon
monoxide and hydrogen chloride) are a greater danger. As long as occupants leave
the area within 15 min of a Halon system discharge, do not reenter it immediately
after a fire, and the space is well ventilated after a discharge, Halon is a safe
fire suppression agent.
Myth 10. Testing diesel fire pumps is bad
I have heard numerous comments from maintenance personnel, such as: "We have reduced
the speed of the diesel driver to lessen wear on the engine." "We would like to
install a clutch between the engine and pump, which we can disengage during our
weekly tests to minimize wear on the engine." "We want to install a high-temperature
cut-out to prevent the engine from overheating."
These points may be appropriate reasoning for a truck or industrial engine, but
they could be the cause for catastrophic losses if a diesel fire pump fails when
needed. The main focus behind any fire protection equipment is maximum reliability
when needed. As such, fire pumps and their diesel engine are intended for emergency
service, not for maximum mileage and wear, as in the case of the truck engine. Therefore,
it is imperative that only the minimum necessary mechanical and electrical systems
be provided, as deemed necessary by the manufacturer, listing agency, and fire protection
experts.
While it is true that wear increases due to poor lubrication when the diesel engine
is started under full load and brought up to its rated speed within 1–2 sec, a fire
pump engine should not log more than 30 hr/yr, including weekly and annual testing.
Excessive wear over the engine's life should not be an issue.
When problems with diesel drivers are occasionally encountered, it is usually due
to poor maintenance and/or operating procedures. For example, infrequent oil changes
can result in corrosion, due to the moisture content in the oil; or leaks in hoses
can result in overheating, due to low coolant level. With the proper care, as recommended
by the manufacturer and NFPA, a diesel fire pump assembly should give many years
of troublefree service. This service is the case with thousands of fire pump installations
throughout the U.S. and the world.
-Edited by Cheryl Firestone, Senior Editor, 630-320-7136, cfirestone@cahners.com
Do sprinklers cause more damage than the fire itself?
According to a study conducted by Factory Mutual, 56% of fires are controlled and
extinguished by three or fewer heads, making the extent of damage from sprinklers
relatively small.
A typical sprinkler head discharges about 20 gpm, meaning that three heads would
discharge approximately 60 gpm. The required waterflow alarm notifies the fire department
and plant personnel so that sprinklers can be secured after the fire department
has established that the fire is out. Thus, in the majority of cases where sprinklers
actuate, fire damage can be expected to be small, and water damage would be confined
to approximately 400 sq ft. Often, total damages due to sprinkler discharge are
less than $5000, and they go unreported.
In contrast, fires have destroyed entire buildings and plants where sprinklers were
absent.
Role of changing hazards
A building constructed as a metal assembly plant had a sprinkler system approved
and installed to adequately protect the occupancy. Several years later, this company
moved out and a plastics manufacturing company moved in.
Their raw materials are thermoplastics, which are stored in racks. The heat release
of a fire involving plastics in a rack storage arrangement is many times higher
than a fire involving metal production operations. In this case, the hazard has
just been increased to the point where the existing sprinkler system would be ineffective.
This deficiency would not likely be picked up during a fire prevention inspection,
nor by the technician who performs the routine testing of the sprinkler system.
The proper evaluation of a fire protection system necessitates information about
the occupancy, the sprinkler system design, and the water supply.
More About Halon
At this time, this author knows of no laws or regulatory agencies in the U.S. prohibiting
the use of Halon as a fire suppressant. In accordance with the Montreal Protocol
on Substances that Deplete the Ozone Layer of 1987, a complete phase-out of Halon
production is mandated by 1/1/2000. However, all U.S.-based firms producing Halon
voluntarily stopped the production of Halon several years ago. Halon is still commercially
available mainly from recycling.
In most cases, the installation of a new Halon system would not be justified due
to the availability of alternative agents. Existing users of Halon can still get
cylinders refilled through many fire protection contractors, although one system
discharge could end up costing almost as much as the installation of a new alternative
system. To have Halon cylinders recharged, estimate about $25/lb, however, this
figure may increase due to future additional taxes.
Note: Halon should not be confused with carbon dioxide (CO2) as a fire suppressant.
Because of the larger required concentrations of CO 2 (34–50%)
to extinguish fires, human life cannot be sustained. The threshold level of CO
2 at which harmful effects become noticeable is about 7%. Therefore,
CO 2 is best used only in unoccupied areas as a total flooding
fire suppressant.
More Info
The author is available to answer technical questions regarding this article. Mr.
Dieken can be reached by e-mail at dominique_dieken@ hsb.com. HSB Professional Loss
Control can be reached at 423-376-1131. The company web site is www.hsbplc.com.
For more information, visit the web site of the NFPA at www.nfpa.org, or the Factory
Mutual web site at www.factorymutual.com.
For general information about this subject, visit the "Fire protection, safety,
and health" channel at www.plantengineering.com.