Fire suppression systems can protect machining centers—and your shop

Machine tools are highly productive marvels of modern technology. They are also fire hazards.

Because they produce chips at high operating temperatures, often with oil-based coolants present, machine tools can easily catch fire. However, if shops plan ahead for this possibility by installing fire suppression systems, they can avoid catastrophic damage to the machine and the shop itself.

A pull-cable, Halon-based, bottle-type fire suppression system, such as this Safecraft AT5AGH, can be installed outside a machine tool’s work compartment. All images courtesy of Safecraft.

For example, one machine shop suffered 12 fires in 18 months. The causes varied, but included incorrectly applied coolant, chip clogging and operator error. The first fire, fortunately, did not cause much damage because it started when an operator was standing at the machine tool and a fire extinguisher was nearby. Had the fire occurred during lights-out production, the results could have been catastrophic.

The 11 subsequent fires, however, were nonevents because after the first fire the shop installed automatic, Halon-based, unitized-cylinder fire suppression systems on all 26 of its machining centers.

A Halon-based, bottle-type system, such as this Safecraft AT5AGH, can be equipped with a heat-sensitive injection nozzle and a pressure switch that can send an “emergency stop” signal to the machine tool.

What to Ask

When choosing an automatic fire suppression system, a machine shop should ask four main questions:

• How well does the system work?

• Does it cause any secondary damage?

• How much downtime occurs when a machine tool’s fire suppression system has to be reset after a fire?

• How much downtime is needed to install a system on a machine tool?

The questions are in this order for a reason. First, if the system isn’t effective, don’t bother. Second, if the consequences of its use cause more damage than would a small fire, the system may not be cost-effective. Third, if a shop experiences repeated fires, it will need to consider the costs of downtime needed to reset the system. Fourth, while installation occurs only once, it still represents downtime.

Different Forms

Halon’s two most common forms are H1301 and H1211. The numbering system gives the Halon’s “recipe.” For example, H1301 consists of one carbon atom, three fluorine atoms, zero chlorine atoms and one bromine atom. H1301 is suitable for fixed-position systems, such as for a machine tool’s working area, and H1211 is for hand-held units.

H1301 exits its container as a colorless, odorless gas and is 50 percent discharged in less than 3 seconds. A typical discharge of H1301 is 3 to 5 lbs. H1211 exits as a low-velocity liquid, allowing a person to see where it’s going and giving him about 15 seconds to direct it appropriately before it turns into a gas. H1301 and H1211 are equally effective on a pound-for-pound basis for extinguishing fuel fires.

Halon does not remove the oxygen from a fire; it stops the chemistry of combustion. It goes right to the nature of a fire—high-speed chemistry—instead of attacking the results of that chemistry. When Halon molecules hit the flame front, they dissociate into active ions that inhibit fuel from combining with oxygen. The reaction time can be in the low milliseconds.

Meeting the Criteria

A Halon-based, bottle-type system is effective because it can quickly suppress a fire in a machine tool’s work enclosure. (A machine tool does not have to be enclosed for a fire suppression system to be effective, but an enclosure helps ensure a Halon concentration level that prevents reignition.) For example, when ignited, gasoline has a rate of flame spread from 700 to 800 ft./min. A Halon-based bottle system can put out a gasoline fire in less than 1 second.