Section 11 - Internal Components
Impact Foam Liner System
In addition to the outer shell, helmets utilize a liner system to provide energy-absorbing zones for the head. The standard material used in these systems is urethane foam. This foam material has demonstrated consistent qualities in absorbing impact and penetration protection based on NFPA, CE, and QAS performance standards.
The original process for manufacturing urethane foam was with the use of Chloro-fluro Carbons (CFC). This process has been changed due to O-Zone depletion via EPA restrictions. CFC’s have been used in many processes such as freon in air-conditioning units until the ban in the late 70’s. Manufacturers that produced urethane foam with CFC’s prior to the EPA regulations were "grand fathered" into the change. Any manufacturer that began production of urethane after the EPA change are prohibited from using CFC’s.
Urethane foam manufactured without the use of CFC’s is a duel edged sword. First, it is a more expensive process. The finished product is created by mixing two chemicals that create the expansion of the material, thus the term foaming. The second result of this new process is a real benefit when used in fire related products. Urethane foam manufactured with CFC as a catalyst, expands when heat is introduced. The CFC reacts to the heat by blowing bubbles expanding the urethane. The down side is that the CFC properties never stop working. That means that a finished foam liner that is exposed to heat at a later time will continue to expand. The new urethane foam process creates a foam liner just like CFC when the two chemicals are originally introduced. However, once the foam liner is formed, this process cannot regenerate expansion under any additional heat exposures. Therefore the liner remains constant and will not change from its original shape.
Inner Liners
Most foam liners are covered with a thermoplastic lining. Often this lining is vacuum formed to match the foam’s interior shape. This inner liner can and is often the platform for support of the headband and attachment points for Velcro that holds ear/neck covers to the helmet. Since the urethane foam can be compressed by hard objects, the inner liner material also serves as a barrier that prevents compression that could result in lessened impact protection.
Headband System
Another important element in helmets is a means of securing a helmet on the head. This is accomplished by using materials that can be adjusted around the head. Most headband systems are based on some nylon or thermoplastic materials. They will be anchored to the helmet with webbing, pins, key sockets or combinations of these components. Adjustment will be accomplished by a ratchet knob mechanism for quick sizing.
These band systems are enhanced for comfort by use of foam padding and FR woven materials. The ratchet component will also be offered with padding that can include a foam backed leather cover.
Beyond the comfort and security of the headband, the headband system should offer the ability to customize fit that must work in conjunction with use of a SCBA facepiece. The helmet fits completely different when in use with the facepiece. When choosing a helmet, sizing and fit should be evaluated with the facepiece prior to selection. What may appear to be a great fit without the facepiece may be disaster when worn with the facepiece.
Chinstraps
Modern day chinstraps are most often produced with webbing materials made of Nomex®. In isolated market locations around the world, some leather chinstraps still exist. Attachment of chinstraps to helmets is accomplished in a variety of ways. Most chinstraps are attached directly to the outer shell of the helmet with some type of screw. Flame resistance, ease of function, replacement and comfort should be the primary concerns in choice.
Chinstraps must have a means of adjustment and release to permit donning and ability to secure the helmet to the head. This is accomplished with snaps, Velcro®, buckles and slide adjustment mechanisms. Most standard chinstraps offer a buckle release mechanism that can also serve as a tension adjustment. These buckles are most often made of a very durable, flame resistant material called delrin. A secondary adjustment is often offered in a metal product commonly called a postman’s slide adjuster. Many chinstraps come standard with both buckle and postman’s slide.
Velcro, or hook and loop material is most often used to provide a means of securing the loose end of the chinstrap webbing to itself. This is simply to eliminate dangling webbing that could snag on equipment worn or contacted during use. However, there is a chinstrap that is offered for helmets that is secured only with hook and loop material. This is a potentially dangerous design. NFPA structural performance defines hook and loop material, and snaps, as a "secondary" means of closure for any system. This means that fire coats and pants must have a "primary" closure system in conjunction with any hook and loop material or snaps. Primary closures are defined as metal zippers, hook and d-ring or any positive locking device. Therefore, if your coat and pants require a "primary" closing system, shouldn’t you expect at least the same minimum for your head protection system?