Fire Suppression Systems

Conservation Report, Ellen Carrlee for the Alaska State Museum
May 2008

SUMMARY RECOMMENDATIONS:
Due to the challenges we have with various systems in this building (computers, pipes, power outages etc.,) the asbestos issue, the degree to which we strive to be prepared for water emergencies, and the limits of technical assistance in Juneau, a wet pipe system is recommended for the ASM collections storage.  Luckily, it is one of the least expensive fire suppression systems on the market, so it would be wise to pursue the best quality product and installation we can.  We may want to consider the possibility of a VESDA system for smoke detection.  Comparisons of various systems listed below:

GAS
*       FM-200 (heptaflouropropane, a halogenated alkane) is a popular replacement for Halogen.
*       FM-200 emits hydrofluoric acid at very high temperatures, but at that point the collection is burned anyway
*       Gas will be propelled with great force giving us the same problems with the asbestos contamination (and object damage from the blast) that we worry about now.
*       In November 2006, a fire suppression system with a nitrogen propellant went off in the Museum of Ethnology in Vienna.  Large numbers of objects were thrown from shelves and damaged, and dust was even blown into closed cabinets.  Since nitrogen is odorless, a marker gas was had been added and it left a tacky film on everything.
*       Rooms must be very well sealed for gas to work well.
*       Pipe modifications must be considered in case different gas has a different flow factor.
*       Health hazard for people exposed to gas.
*       Many jurisdictions require sprinkler systems in addition to chemical suppression systems
*       Re-charge period is a time of vulnerability

WET PIPE
*       This is the most common fire suppression system, with good track record and fast response.
*       Simplicity and reliability, the fewest number of components to go wrong.
*       Low installation and maintenance expense, ease of modification with renovations.
*       Winterthur Conservation department went with a wet pipe system due to cost and its proven effectiveness.
*       UAF Museum of the North has wet pipe with VESDA in collections storage for higher levels of smoke detection. 
*       Regular maintenance includes discharge to the outside through an external valve.  At this time, valves, pumps and gauges can be verified.  This ought to happen monthly.
*       System should have flow monitors and pressure gauges to monitor pressure on both sides of the valve when closed.
*       Must be shut off manually
*       Top causes of failure are freezing temperatures or knocking off a sprinkler head.
*       Typical sprinkler head releases 25 gallons per minute (GPM).  A fire hose releases 150-250 gallons per minute.
*       Depending on the source cited, 60-80% of fires are put out with 1-2 sprinkler heads.
*       Failure rate of 1 head per 16 million installed annually.
*       Short down time after a fire…replace the sprinkler heads and turn the water back on.
*       Heads may have a fusible element that melts or a “frangible glass bulb” with liquid inside.  The bulb is color coded and ruptures at a certain temperature.

DRY PIPE
*       A dry pipe sprinkler system is one in which pipes are filled with pressurized air or nitrogen, rather than water. This air holds a remote valve, known as a dry pipe valve, in a closed position. When fire causes the seal in the sprinkler head to melt, the gas pressure is released and the flapper valve opens, allowing water through.
*       Commonly used in areas prone to pipe freezing, like warehouses, attics, outdoor loading docks etc.
*       Longer delay for response, up to 60 seconds from the time a sprinkler head opens until water comes out.
*       Failure of the compressed gas means the pipes fill with water, but as long as the seals on the sprinkler head are not melted the water will not come out.
*       Corrosion of pipe can happen, cause failure from rust on the inside
*       Must be shut off manually

PRE-CONDITONED DRY PIPE
*       Like the dry pipe, except valve is activated by electronic sensors.  There are two in each zone, and both must go off to activate the system.  If one is not functioning, neither does the sprinkler.
*       System is computer controlled
*       There is a manual release possible, but it must be located where it can be safely reached.
*       Some fire marshals may require a demo to prove it is working (ie flooding the pipes)
*       Corrosion inside pipe can make a rust-water sludge that gum up the pre-action valve.
*       Higher cost of installation and maintenance, modification is difficult.
*       Given the troubles with our building, pipes, computers and so on, a system this complicated is rife with things to go wrong.

MIST
*       Water is released at high pressure (1000 psi) pressure is made by gas or a high pressure pump.
*       Water supplied by a water supply pipe, dedicated tank or canisters.
*       Discharge triggered by electronic sensors.
*       Technology is not as old as other techniques, only available in the US for about a decade.  Research began in 60’s but has been spurred on only recently as Halon is out and there are new regulations for fire suppression on board ships.
*       Common in the cruise ship industry?  The National Parks Service and the Shelburne Museum in Vermont have been investigating its use.
*       Only a few gallons of water required to put out a fire.  Much less water damage.
*       3-D array of pipes is needed throughout the room with a nozzle every few feet.  Piping is ½” diameter stainless steel pre fabricated and then assembled on site with simple compression fittings.
*       Efficient, very little water needed, so less damage from water.
*       Small particles are thought to bind up smoke particles and result in less soot damage
*       Time of vulnerability if canisters need to be replaced.
*       Pumps require backup power supply.
*       Effectiveness to date is based on experimental and computer monitoring, so there is no track record to go on.  How it works is very elegant and appealing, but largely theoretical.
*       One aspect is that the tiny droplets give an increased surface area, helping to reduce temperature and oxygen faster in the space.  Droplets turn to steam and bind up available oxygen, acting rather like a gas to smother the fire.  This only works well in a large fire.
*       Possible problem of obstacles and structures…if the mist cannot get to the flame in a smaller fire it takes longer to put it out?

DELGUE SYSTEMS
These are wet or dry pipe systems that include open heads that just let the water flow, instead of heads that release as needed.  Also called “automatic” heads.  Not recommended for museums, but this is the kind of system we see in the movies.
Recommended for high-hazard areas like power plants, chemical storage and aircraft hangars.

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One Response to Fire Suppression Systems

  1. I work building the fire suppression systems and this article is spot on, brilliant stuff here!

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