Issue



Where there's smoke...there's cleanroom disruption


02/01/2004







BY LAURENCE GRODSKY

Click here to enlarge image

With the introduction of higher insurance premiums and deductibles, high-tech manufacturers are on the prowl for the latest in fire suppression systems


By their very nature, cleanrooms are very difficult environments in which to combat fire. The latest technologies, however, can help prevent a fire from even starting, let alone spreading.


From the outset, it must be understood that fire protection is a multistage process in which fire protection equipment must be deployed; but remember, a strong prevention plan must be established. Protecting lives, property and your business from fire requires planning, guidance and the full cooperation of all the building's inhabitants.


When it comes down to it, education is actually the most important task in fire prevention and protection, as all the fire prevention techniques and planning simply can't insulate an organization from a fire incident. Even though fires are rare incidents, they do occur and can be extremely devastating to the operations and profitability of an organization-especially in today's global manufacturing environment.

On top of globalization, businesses have also been experiencing increases in insurance premium costs and higher deductibles. With both of these issues creating new challenges and risk, there's never been a more important time to increase prevention and suppression techniques.

Equipment damages or losses that were routinely replaced through fire insurance coverage in previous years may now be the responsibility of the victim company. With this in mind, high-tech manufacturers are attempting to search for new products and methods that will limit or mitigate their exposure to this new insurance risk more than ever before.

How a fire develops

The combustion process begins before you see smoke or fire or feel intense heat. The initial development of a potential fire will emit the colorless, odorless by-products of initial combustion.

Once these particles are present, the fire is said to be in its "incipient" stage of development. This stage will eventually transform into the smoke, followed by the flame stage and finally the intense heat stage. The "incipient" stage causes no damage to any equipment and is not a danger to any inhabitants and the environment.

In fact, the impending damage that will occur in the subsequent development stages of a fire can be prevented by removing the source of the combustion either through the removal of power or heat from the overheating source of ignition. Actually, you can turn a potentially developing fire into a maintenance issue—no loss of equipment, no danger to the inhabitants, no business interruption, no insurance losses, and no lost revenues. This technology will be addressed later.

"Must haves" for protecting your investment

Fire protection systems encompass two functions: the detection/notification of a fire, and the subsequent suppression of that fire. Detection systems rely on various types of detectors to sense problematic conditions, either being smoke, flame, heat or the presence of products of combustion.

Each type of detection device is used for specified conditions. Semiconductor manufacturing facilities present a unique environment for fire protection. The airflow tends to inhibit the function of standard spot smoke and thermal detection devices due to the resulting smoke movement.

In semiconductor fabs, smoke will follow the laminar airflow rather than the traditional movement towards the ceiling, whether with little or no airflow conditions. Combined with the passive function and sensitivity of a standard spot detector, all types of ceiling detection will provide limited protection for the cleanroom facility.

Proper protection of cleanrooms typically found in semiconductor fabs calls for locating a detection device within the airflow where the entire room can be monitored properly. An appropriate location is typically within the airflow immediately before the air-handling unit where the dilution of the air occurs, as well as at the exit of both the air-handling and re-circulation handling units.

The detectors can provide passive or active detection but are required to provide a minimum sensitivity level of .03 per foot obscuration. The National Fire Protection Association (NFPA) has published Standard 318, "Protection of Semiconductor Manufacturing Facilities," which specifically indicates the location of approved detection devices as well as sensitivity and other characteristic requirements.

Potential detection devices in addition to smoke detection may include optical flame detection and gas detection as indicated by NFPA Standard 318. For highly-advanced manufacturing sites, water sprinklers have proven to be an effective life safety suppression agent, and are required in accordance with NFPA Standard 318. For minimum protection, sprinkler head locations should include the room as well as exhaust ductwork, plenum, and interstitial spaces above the room only if they are constructed of materials that are combustible.

Still, assets that reside within that facility are at risk. Water, by nature, can damage sensitive electronic circuitry, and sprinkler systems have potentially high clean-up costs.

To mitigate potential damage and losses, a clean gaseous agent can be considered as a supplemental (but not replacement) protection system to a sprinkler system.

By discharging a clean agent system before a sprinkler system engages, the agent, in most cases, will suppress a fire without injuring the inhabitants and will spare sensitive electronic equipment.

The clean agent systems, in most cases, will require deactivation of air-handling units. If this doesn't occur, the clean agent system may not successfully suppress the fire, in which case the standard sprinkler system can be employed to protect the facility and any workers who are still in the room. Remember, if the sprinkler system is employed, the assets within the protected structure will be either damaged or lost.

How HFC227ea works

Clean gaseous agents are safe for humans and will not damage sensitive electronic equipment; however, selection of preferred gaseous agents vary from country to country.

Fire-suppressing gaseous agents are typically an alternative to water for the protection of electronic equipment. Historically, Halon 1301 was the gaseous agent of choice for the applications discussed in this article; however, the Montreal Protocol, ratified globally more than ten years ago, placed a moratorium upon the production of Halon 1301 in the majority of nations due to its ozone depleting characteristics. Since then, the U.S. and Europe have taken a different approach to suppression.

In the U.S., the Environmental Protection Agency (EPA) accepts the use of the next-generation halocarbon (HFCs) HFC227ea, a product that has no ozone depletion effects and makes a limited contribution to the greenhouse effect. Commonly employed across the U.S., the gas is safe to inhale at design concentration levels and extinguishes fires without damaging sensitive electronic equipment and other materials.

In Europe, inert gases, including carbon dioxide, nitrogen and argon, are widely used as suppressants. Since they are derived from the atmosphere, they have arguably no overall effect on the environment; however, they are required in much larger quantities and must be stored under much higher pressure than HFCs such as HFC227ea.

Typically, an inert gas suppression system will need five to 10 times more cylinders of gaseous agent at 2,000 psi than HFC-227ea at 360 psi. Also, inert gas delivery systems have to be built to high-pressure specifications, and higher levels of concentration are required for suppression.

Typically, a seven-percent concentration for HFC227ea will suppress a fire while inert gases will need 35 to 50 percent concentrations. HFC227ea is also stored as a liquid and releases into the air as a gas. Inert gases are always stored in the gaseous phase, which is why much larger volumes, logistical effort and greater storage capability are required.

A high-tech approach

As discussed earlier, the interruption of the combustion process during the incipient stage of a fire will prevent any equipment damage and will not effect inhabitants or the environment. Recent technology advancements are available to provide such detection.

For example, Siemens employs the use of Very Early Smoke Detection (VESDA) with its core fire alarm panel products. VESDA is an aspiration detection system that draws in air and examines it with laser particle detectors.

Units can indicate a possible fire before smoke can be smelled or flames seen. By identifying a fire at the incipient stage, notification allows damage, if any, to be limited and personal injury to be prevented.

With incipient fire detectors, a system can detect overheating wire in an electrical installation before it reaches flash point. In this case, there is no need to deploy the suppression system, because the circuit can be identified and simply switched off. The fire has not yet occurred.

Such intelligent systems are the future of fire detection and can save lives and investments. And with increasing insurance premiums and higher deductibles, the use of VESDA systems and FM-200, along with required sprinkler systems and a state-of-the-art fire alarm system, can be your best insurance policy for your critical assets.

LAURENCE GRODSKY is business manager for Siemens Fire Safety. Grodsky can be reached at: fiswebmaster@sbt.siemens.com