Before committing the extensive resources needed to develop a new intumescent technology for doors, ZERO conducted an exhaustive search for suitable intumescent material from other sources. In that search, we applied very specialized criteria based on the unique requirements of door assemblies:

• Relatively low intumescing temperature

   At approximately 250-300^oF (121-149^oC), even better-quality neoprene rubber in smoke control seals begins to disintegrate and lose its sealing properties. Any lapse in protection until intumescent action begins at higher temperatures would allow passage of smoke and toxic gases in potentially life-threatening volume.

• Slow, continuous expansion

   Gradual expansion is important to ensure that the material infiltrates even the smallest spaces--and that the opening can be resealed after escape doors are opened. If the material expands all at once, there will be no reservoir for this purpose.

• Moderate expansion force

   A fire-rated door must remain latched when exposed to fire. Intumescent materials that expand with too much force increase the probability of latch failure allowing the door to be forced open or to fail in a test.

• Firm insulating char

   The flame-resistant, carbon and graphite barrier formed by intumescent action must be structurally solid. A "weak" or loose char can cause fire-door assemblies to fail the hose stream test portion of U.S. fire tests.

• Long shelf life for both outside and indoor applications

   Inactive during day-to-day door operation, intumescent material must perform in the emergency. There are no second chances. Proper product application and installation help to protect intumescent material from potentially degrading forces, but manufacturers do not usually have control over how their products are installed. Long shelf life is essential for reliable, consistent performance.

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   Other criteria identified by ZERO included expansion volume and, especially, cost. Material flexibility was particularly important because OEMs would want to retain existing designs and production equipment. Low flame spread and smoke-developed index were additional requirements, and the material had to be halogen-free in keeping with environmental regulatory trends.

   Following an exhaustive search, Zero found no existing domestically produced product that satisfied all of the essential criteria for door applications. This finding was not unexpected in view of the origins of most available intumescents, which were designed and manufactured specifically for the firestopping and fireproofing industries. Requirements for applications in those industries are different from, and sometimes diametrically opposed to, the needs of door openings.

   Typically, these materials activate at a high temperature, beginning around 500^oF (260^oC), and are designed to expand with sufficient force to crush burning PVC pipe and other melting penetrants. Most of those products expand all at once to fill the gap instantly, emptying the reservoir, and form a relatively weak char. Reports of poor shell life and unreliable performance have been a chronic problem that continues to plague this sector of the industry.

   Because of their common characteristics, ZERO uses the term "HARD PUFF" to refer to this class of conventional intumescent materials. Our research team reached the conclusion that those materials are not the best solution for dynamic door openings. Because of the critical life-safety risks of inferior performance and improper application, Zero chose not to compromise. The two-year development effort that followed lead to a new SOFT PUFF^TM technology, which is uniquely suited to the special needs of door assemblies. INTUMET intumescent material is the product of that technology.