Paul M. Fitzgerald
President and chief executive officer
Factory Mutual Research Corp.
To the Editor:
The article “Cleanroom fire-safety debate heats up” by John Haystead, which appeared in the April 1998 issue (CleanRooms, page 1), was informative and balanced. However, I would like to clarify Factory Mutual`s position and approach to cleanroom fire safety, and comment on some of the issues raised:
The Fire Propagation Index or FPI (mistakenly referred to in the article as the Fire Protection Index) represents the rate at which material becomes involved in a fire. A material with an FPI of 6 or less will not propagate a fire beyond the ignition zone.
The recent severe loss experience in Asia was cited as being the driver of Factory Mutual`s approach. In fact, the fundamental research initiative that led to the development of performance measures such as the FPI began in 1985. Concern over the cleanroom environment was one of the major reasons for undertaking this initiative even back then. More recently in 1994, because of U.S. loss history and loss potentials, we became even more concerned about cleanrooms. The more recent Asian experience just confirms that these concerns were justified.
We share the industry`s concerns about the process compatibility of materials meeting the 4910 FM criteria. To address this, Factory Mutual Research Corp. (FMRC) and SEMATECH have initiated a combined project to develop comparable indices for leaching, outgassing and chemical resistance. It is expected that the results of this joint project will provide further guidance of their acceptability and use.
The article commented that these new materials cost up to five times more than ordinary materials. A recent cost analysis by a manufacturer, however, concluded that these new materials would comprise a maximum increase of about 4 percent of the cost of a fully automated wet bench. Thus, the use of these high-performance materials would have a very minor impact on the overall cost of a tool.
Questions were raised on the repeatability of results from the test apparatus we use. During its early stages, we experienced some setbacks in replicating our original instrument. These setbacks were overcome and today, we have two instruments that provide consistent, repeatable results.
The portrayal of Factory Mutual`s recommendations on the use of fire suppression systems was not clear. First we have always recommended that wet benches and other processing tools be constructed of non-combustible materials. The use of fire suppression systems is a less desirable alternative because of the potential for a large fire with greater resultant damage occurring. Second, our objective in developing materials that meet our 4910 test criteria was aimed at providing the industry with an alternate to providing suppression systems. These materials provide nearly all of the advantages of non-combustible materials, while retaining the process and cost advantages of the combustible materials currently used in this sensitive, dynamic occupancy.
Finally, we welcome other testing laboratories to adopt the 4910 Standard for testing these materials. We have submitted the standard and apparatus for public recognition. We are finalizing negotiations with a manufacturer to produce the apparatus. Copies of the 4910 Standard are available to the public by contacting the FMRC Technical Information Center.