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Hoods 101: What they do and how that's tested
This necessary, but overlooked, component of the protective ensemble is vital to firefighter safety
A firefighter's protection is incumbent on the entire ensemble working together to insulate the firefighter from the hazards on the fireground. This ensemble has the obvious elements of the protective coat and pants, helmet, gloves and footwear. Yet, a critical and often neglected part of the ensemble is the protective hood.
Hoods are actually an interface component of the ensemble. That is, they provide protection to the gaps that are created by other parts the ensemble coming together. As it turns out, the head and face region is such an area.
Hoods are supposed to provide base protection in the potential gaps on the sides of the face and on the neck, which are not complete covered by other elements of the ensemble. In reality, the hood should never be the only area that is protecting any portion of the face or neck.
The coat collar is intended to protect the majority of the wearer's neck. Ear covers deployed from the helmet are intended to protect the back of the head and the sides of the face to the SCBA facepiece. These items in conjunction with the hood actually provide two layers of protection.
Simple piece of clothing
The protective hood itself is a relatively simple piece of clothing. Constructed similar to a ski mask, the hood's face opening is intended to surround the SCBA facepiece; its extended front, back and sides is known as the bib.
NFPA 1971 sets extensive requirements for hood design and performance for structural and proximity firefighting. For design, these requirements include the minimum length of the bib and minimum dimensions for the face opening, including the circumference for which the hood opening can be stretched. The certification organization assesses the compliance of the hood design by making some of these measurements for hoods using a standardized head form while other measurements are made with the hood lying flat.
In general, hood openings are circular or oval and the dimensions are set to accommodate industry SCBA facepieces. Some manufacturers may shape their hoods in a pattern that is more representative of the general shape of the facepiece.
Hoods also can be sized specific to certain types of SCBA facepieces and when this approach is used, NFPA 1971 requires that the face opening overlap the facepiece by at least a half an inch.
For the most part, the face opening is constructed using an internal piece of elastic that is set at the right tension to close around the facepiece but not so tight that an individual cannot put their head through the opening as most firefighters do.
Bib lengths vary. The minimum dimensions are set by NFPA 1971, but most manufacturers also provide a variety of lengths and designs. It is important for hoods to be long enough to stay under the collar when worn and during head movement. Many bib styles extend longer in the front and back than at the sides, providing a contoured appearance. The bibs may be rounded or squared off.
Hood materials are almost exclusively knit fabrics. Common fabrics include 100 percent Nomex or similar Aramid and PBI, P-84, and Nomex blended with flame-resistant Lenzing (rayon) or Kevlar. One of the new fabrics in use is based on a carbon fiber that is typically blended with a different fiber.
All standard hoods are constructed of a two-ply or layer design, which is needed to meet fabric performance requirements. As knits, hoods possess a large degree of elasticity and come in one size. Some specialty hoods include non-knit materials similar to turnout clothing or use extra layers to create more insulation.
Protective hoods are subject to a number of performance requirements that are similar to those applied to protective garments such as coats and pants. For example, materials used in the construction of the hood must demonstrate flame resistance before and after washing.
The hood is tested on a head form in a special oven for heat resistance at 500 degrees Fahrenheit for 5 minutes and cannot show any evidence of melting, separation or ignition and cannot shrink more than 10 percent from the extended heat exposure. The thread used in sewing the seams must be of an intrinsically flame-resistant fiber that does not melt under a temperature of 500 degrees.
The only insulation requirement that is applied to hoods is thermal protective performance testing. This is the same test applied to garments and gloves. However, for hoods a lower TPP rating of 20 calories per square centimeter is the minimum requirement as compared to a rating of 35 for garments and gloves. This is because hoods are not intended to be the principal protective layer.
A unique requirement for hoods is an evaluation of the ability for the hood face opening to retain its size after repeated use. For this purpose, sample hoods are repeatedly put on and taken off a standardized head form. The original measurements of the face opening are compared to the same measurements there taken after 50 cycles of donning in doffing.
According to NFPA 1971, the hood face opening dimensions cannot increase more than 10 percent based on this test. However, in our opinion after viewing the test, the head form is too small and does not do a good job of making this assessment. It would be rare for any hood to fail this requirement.
In the standards development arena, hoods do not get too much attention during the review of NFPA 1971. In the recent revision, some changes were made to the hood requirements, mainly to clarify test requirements but with the one notable change of setting minimum hood face opening circumference.
Unfortunately, some careless changes to one particular requirement have necessitated a series of amendments, which will forestall the availability of many hoods being certified to the 2013 edition. In most cases, certifications of hoods to the 2007 edition of NFPA are valid through the end of August.
Even though protective hoods may seem like a commodity or an accessory, they are a vital piece of your overall protective ensemble. They provide a significant level of thermal insulation in hot environments but only when the full ensemble is properly donned — collar in a raised position and ear flaps deployed.