Although the DuPont Company’s Nomex aramid fiber was the first material used for the construction of protective hoods for firefighting applications, manufacturers are now using several different fibers, and combinations of fibers, in the construction of this key piece of firefighter protective clothing.
As with all elements of the firefighter protective clothing ensemble, minimum performance specifications for hoods are spelled out in NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting (2007 Edition).
NFPA 1971 specifies that protective hoods may have a lower thermal insulation requirement than garments — a thermal protective performance (TPP) rating of 20, compared with the minimum 35 TPP required for garments — but still must meet all of the flame- and heat-resistance requirements associated with garment materials used in the ensemble.
Blending fibers
Manufacturers have responded to this requirement using a variety of construction designs — heavy, single ply or double ply — using Nomex, Kevlar, polybenzimidazole (PBI), P84, Basofil (a melamine fiber that blends with commodity fibers and synergistic high-temperature fibers), and fire-resistant rayon fibers like Lenzing FR.
Nomex and its chemical cousin, Kevlar, are aramid fabrics that are similar in their basic structure. The term aramid is a combination of aromatic polyamide.
Aramids are fibers in which the chain molecules are highly oriented along the fiber axis to exploit the strength of the chemical bond. Nomex and Kevlar are frequently used together in composite fabrics for their fire-resistive properties (both fibers) and for the strength of Kevlar.
New players
As newer fire-resistant fibers have been developed — such as PBI, P84, Basofil and Lenzing FR — protective hood manufacturers have been ardently at work designing hoods that make use of composite fabrics for their synergistic affect, where the whole is greater than the sum of the parts. They are using these newer composite fabrics to create hoods that are more durable, better fitting, more comfortable, and yes, more colorful. Browse the Internet and you’ll find firefighting protective hoods in all colors and many original designs.
Being fashionable is a good thing, but let’s not forget the hood’s mission: to serve as the critical interface that links the protection offered by the firefighting helmet, the SCBA face piece and the protective coat.
The hood also serves as the backup thermal protection provided by the helmet. In the event that helmet becomes dislodged, the firefighter properly wearing the hood would still have a measure of thermal protection in place.
Some of the more recent improvements in hood materials and construction have focused on increasing the comfort while decreasing the risk of heat stress. Newer hood designs incorporate fabrics that blend high performance, non-flammable, carbon-based fibers (fire resistance) with durable para-aramid strengthening fibers, like Kevlar, that provide protection from mechanical hazards.
Rayon and breathability
Manufacturers are also using Kevlar and PBI in combination with FR rayon fibers, such as Lenzing FR, to create hoods with greater breathability. The fiber properties of rayon — rayon is produced from wood — offers good protection against heat and flame, while keeping the body drier and cooler than synthetic fabric blends, thereby reducing the risk of heat stress and heat stroke.
These newer composite fabrics are enabling the hood manufacturers to produce protective hoods with TPP ratings greater than the 20 minimum required by NFPA 1971 — some with TPP ratings as high as 28 — while still achieving greater breathability and comfort.
The basic design of fire-fighting hoods has only changed minimally since the first models became available. Yet newer hoods have construction features such as longer bibs and side notches, designed to help keep the hood in place under the protective coat.
However, the greatest improvements have been, and will continue to be, in the development of the fire-resistant fabrics that continually improve the hood’s performance as an integral component of the structural firefighting ensemble.
