Focus On Respirators:Two Hood Type NBC Respirators

by Christopher T. Carey

In today's individual NBC respiratory technology, there are two design approaches. The most common is the "face-fit" mask, e.g., the conventional military style respirator; the second is the hood style respirator that covers the wearer's entire head. Face-fit respirators are necessarily expensive due to the extensive ergonometrics required for their successful design and effective development. Face-fit respirators must consider facial physiognomy and variations peculiar to applicable populations. Face-seal problems include challenges posed by facial hair growth, variations in oronasal shape, conformation and dimension considerations (seal contact area), and vision requirements.

Interestingly, the "whole-head hood" style respirator is one of the oldest concepts employed in the "modern" era of CB warfare; an early example was the British PH Helmet WWI. Until relatively recently, most respirator R&D has been dedicated to the face-fit style mask. Only after the 1991 Southwest Asian"Gulf War" renewed awareness of the importance of providing adequate, quick donning and easy to use civilian protection equipment was more thoughtful reflection given to the need for development of well-designed, durable and cost-effective individual respiratory protection that could fit a wide range of head sizes. While a small number of the fully head-enveloping NBC respirators have been available over the past several decades, the advantages offered by the whole-head respirator today assume increased importance as the world faces an energing NBC threat posed by extremists and terrorists. This threat assumes even greater importance because biological agents are perceived as today's preferred terrorist weapon, fostering concerns of potentially providing effective civilian respiratory protection for large numbers of individuals.

Two hood type protective designs, eminently suited for use by a diverse range of civilians and age groups, exemplify current design concepts, the American ILC Dover, Inc. D.E.R.P (Disposable Eye Respiratory Protection) and the Finnish KEMIRA SAFETY Civic Chemi-Hood. Although both share marked similarities in providing civilians with easy to use protection against CB attack, the ILC Dover product was developed as a disposable, single use item that meets all of the immediate requirements for protecting the wearer against all concventional CBW agents. The Kemira Chemi-Hood, which may also be considered "theoretically disposable", was designed to give somewhat more prolonged protection capability--an observation underscored by its acceptance of a standard screw-thread type NBC filter. The disposable ILC DERP, by contrast, has twin, fixed bilateral filters, making it a bit less capable of providing potential multiple exposure usage. Despite these differences, both designs provide excellent emergency protection, based upon an examination of their performance specifications, and both offer considerable versatility across a broad demographic spectrum. Further, both the DERP and the Chemi-Hood respirators are extremely well conceived, researched, engineered, and economically produced solutions to providing mass individual protection of the highest level at a relatively low cost outlay.

Originally designed in cooperation with the US Army, as emergency supplemental NBC protection for civilian workers, the ILC Dover DERP shares many similarities with other pioneering ILC hood style designs. It provides up to two hours of protection against nerve and blister agents, may be used effectively by individuals with long hair and beards, and is capable of being donned in less than 15 seconds. The DERP comes in a sealed impermeable plastic bag and may be used up to 30 days after the bag is opened. Shelf life of the sealed DERP is given at 10 years. The mask and its construction materials were specifically designed to provide complete protection while resisting high temperatures; the DERP may be stored at temperatures exceeding 165F, without impairing functional service capability, and is capable of providing full protection in temperatures as low as -20F. The field of vision is excellent due to the transparent broad face section and the oronasal nosecup portion of the mask provides very low internal deadspace with consequent low CO2 accumulation. Additionally, the total weight of the DERP respirator is only 1.4 pounds, which makes it extremely lightweight and easy to carry.

The Chemi-Hood by Kemira Safety Oy of Finland is visually very similar to the DERP, although the Kemira respirator uses a conventional screw-thread NBC filter (Kemira Combined NBC Filter ABEK P 15, but the unit accepts any NATO spec filter). Both whole head hoods use a neck-sealing dam and are "un blown". Like the DERP, the Chemi-Hood provides excellent, unimpaired vision, and accommodates a wide range of potential users--from 12 year old adolescents through adults. The Kemira Chemi-hood has a specified shelf-storage life of 10 years and the material used for the hood has high temperature resisting characteristics. The plastic hood material also resists mustard agent for more than 24 h. The Chemi-Hood comes packed in a plastic hardshell container fitted with a carrying strap, which provides storage protection, as well as ease of portability. As with the DERP, the Chemi-Hood is quick and easy to don. Both the DERP and the Chemi-Hood feature secondary protection to the shoulders through draping of the hood skirt material.

These two excellent examples of the "not-actively blown" hood type NBC respirator are noteworthy in that they provide the highest protection possible at an extremely low cost per unit for the broadest range of individuals. Furthermore, they can be considered expendable emergency protection in either normal, unusually warm, or severely cold climates.

Inquiries about the American made DERP may be directed to Mr. John McMullen, Marketing Manager of ILC Dover, Inc., (Tel: 302.335.3911 / fax: 302.335.0762);

Information concerning the Chemi-Hood may be obtained from Mr. Markku Latvala, Marketing Manager of Kemira Safety Oy, Finland (Tel:+358.6.3258.511 / fax: +358.6.3212.671).


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