Design for a mill building in the metals industry is a study in Performance Based Design. Most often, the facilities will be constructed entirely of non-combustible materials. Per the International Building Code, mill facilities are usually rated as F2 (low hazard factory/industrial) occupancies, which means that they qualify for unlimited area and height without sprinkler systems.
Given the costs involved for equipment, insurance carriers and Owners typically approach fire protection requirements by addressing specific hazards within the mills. This is accomplished with small sprinkler systems or other suppression systems that are not water based applied to equipment or rooms. Detection systems will be similarly installed based on anticipated hazards. Obviously, any systems that are prescribed by the Building Code, such as storage areas, will be provided with fire protection systems in accordance with those Codes.
One of the special hazard areas of mill buildings that seems to generate the most discussion when contemplating the fire protection scheme is electrical equipment rooms (EERs). These room typically have VFD's, transformers, and motor control centers. Given the equipment involved, these rooms can potentially have medium voltage electrical equipment. This discussion focuses on the approach that the fire protection engineers at Gulf States Engineering take for EERs.
In the United States, during the period from 2006-2010, statistics indicate that only 7% of industrial structure fires originated in electrical systems. Using electrical origination of fires as a case for the protection of the systems at a typical mill building, it must be noted how a typical electrical fire starts. The typical modes of ignition in electrical fires are:
Looking at the sources of ignition, arcing is generally caused by:
Excessive resistive heating is generally caused by gross overloads, stray current or ground faults, or poor connections. Except for the case of lightning, tests have shown that the majority of these fires led only to the scorching or smoldering of combustibles.
Given these typical types of electrical fires, we desire to detect any fire in its incipient stage, before flaming combustion commences. For this reason, we typically propose to provide air sampling smoke detection as our first line of defense against electrical fires. This smoke detection method allows an Owner to detect a fire prior to flaming combustion, so that methods may be employed to mitigate any damage from a fire. Some of these methods would include operator notification to commence shut downprocedures or manual fire extinguishing methods via a portable fire extinguisher.
In 2001, the United States Air Force issued Engineering Technical Letter (ETL) 01-18 based on the results of an assessment of the risk associated with equipment damage coupled with the installation of clean agent systems in server rooms. This study found that for all of the money being spent on installation and maintenance of clean agent systems, there was no benefit to the Government because the risk of equipment damage to electronics was not changed. Consequently, the US Government has revised their guide specifications for facilities (Unified Facility Criteria)to no longer install clean agent systems in rooms housing electronic gear, except for those deemed as â€œnecessary for national security.â€
Based on the expected types of electrical fires, it is of utmost importance that mill Owners detect any fires early, prior to any equipment damage. Given that, the primary means of fire protection should be an early warning fire detection system, such as the air sampling smoke detection system.
Secondarily, GSE would typically recommend the placement of water mist or CO2 portable fire extinguishers. An additional component of a fire protection system, when required by the insurance carrier, should be the installation of a water-based sprinkler system. Since the bulk of electrical fires will be smoldering type, a sprinkler system is not the primary means of protection from fire.