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FIRE PREVENTION TRAINING

Safety Article by Harold Hough August/September 2008

I became familiar with John McCain long before he became a presidential candidate or even a senator. In fact, he was still recuperating from his 5 ½ year stay in the Hanoi Hilton when I first saw him in a film.

It wasn’t the type of film you expected McCain to be in. At Naval Officer Candidate School, we had to watch a film called “Learn or Burn.” It chronicled the USS Forrestal fire and one of the scenes I remember was an A-4 pilot escaping his burning aircraft by climbing over the plane’s nose. Little did I know that in future years I would be voting for that pilot as both senator and president.

Although McCain’s cameo appearance in the movie is probably the highlight of the movie today, the theme of the movie was how important it is to properly fight fires. Although the Forrestal had good firefighting systems, untrained firefighting crews were actually making things worse by using the systems improperly.

Although you hopefully will never have to fight a fire onboard a ship, some of those lessons apply to fighting a fire in a mine. And, the most important lesson is to know the systems and what they can do. The result of not knowing these could be more fire damage and curtailed operations at the mine.

If you are looking for a new subject for your next safety training class, you might want to think about explaining the site’s sprinkler system, what it can do, and what it can’t do. It also pays to make sure your workers know the signs of a faulty sprinkler system.

WET SPRINKLER SYSTEMS

The two most common sprinkler systems are wet sprinklers and dry sprinklers. While they are both effective, they operate in different ways and have different weaknesses.

The wet sprinkler consists of a continuous water supply (usually in a tower), thermally activated sprinkler heads, and assorted valves. The sprinkler heads are located in such a way that they should give 100% coverage of the floor space.

Wet sprinklers are normally pressurized to about 125 PSI via an elevated water tank. The tank, in turn, is connected to the local water supply.

A wet sprinkler system is activated when a bulb in a sprinkler head is broken. The bulbs usually are made of thin glass and contain a colored alcohol mixture that indicates the temperature at which it will burst (some bulbs are made of low temperature metals). Usually a red bulb is designed to burst at 165 degrees Fahrenheit, while a green one will activate at 200. However, these settings aren’t standard and one has to check the manufacturer’s data sheets.

When the temperature in a room rises due to a fire, the low temperature metal will melt or the alcohol filled bulb will burst, allowing the water to escape from the sprinkler. The high pressure water hits a disk below the opening, which breaks the stream up into a fine mist that covers more space.

When the system detects a loss of pressure an alarm goes off. As long as only one sprinker head is open, the system can readily maintain its pressure. However, in a larger fire, where several sprinkler heads activate, the system pressure will drop enough that an electric pump will kick on to keep water pressure up. If pressure continues to drop, because of a large fire or a power outage, a diesel powered pump will kick in.

The advantage of this system is that it can provide more water pressure and isn’t as susceptible to water pressure problems from the local supply. Otherwise, a large fire could drastically affect water pressure in a small community water system.

The weakness of a wet system is that the lines are always charged with water, which means a leak in the pipes will cause water damage.

DRY SPRINKLER SYSTEM

The dry sprinkler system has the same arrangement of sprinklers as the wet system. The difference is that the sprinkler pipes are dry and pressurized with air. When a sprinkler head is activated, the air is released from the system, which causes a large pressure drop. This, in turn, activates a spring loaded check valve connected to the main water system. The pressure of the of the water main forces the check valve open and sends water though the sprinkler system to the activated sprinkler head.

When the fire is over, the water supply has to be physically turned off, the activated heads replaced, the system is repressurized, and the main valve reset. This entails opening the inspection cover of the valve, manually resetting the valve, and activating the locking pin for the check valve. Then the inspection lid is closed and sealed.

By keeping water out of the system, there are fewer problems with leaks and corrosion associated with standing water in pipes. However, the problem is that the system’s water pressure is no better than that in the water main. If water demand cuts the water flow, this system can suffer.

No matter what system you have at your operation, it is important to let your workers know how it works and what its strength and weaknesses are. They should know where the system lines are in their working spaces, in addition to any valves or pumps that are critical to operation. They should also know some of the signs of trouble like leaks or damaged sprinkler heads. And, finally, they need to know what sprinklers can and can’t do.

Although it’s important to teach workers about fire extinguishers, it’s critical they know what the second line of defense, the sprinkler system, can do. Knowing about fire extinguishers and fire sprinkler systems can mean the difference between a small fire, with little damage and a major fire that can cost your mine millions of dollars in damage and lost production.