DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The helmet that is worn by aircrews has several functions that must be maintained even during nuclear, biological and chemical (NBC) manoeuvres where NBC protective clothing must be worn. These functions include protection of the head in the event of a crash, protection of ears against excessive noise and the provision of means for electronic communication. An NBC chemical protective hood when worn under the headgear along with a respirator should not cause discomfort to the wearer, or at least should minimize any discomfort, and it must allow the functions of the helmet to be maintained at an acceptable level.

[0019] An incompatibility problem involving the present in-service aircrew chemical protective hoods and aircrew flight helmets exists. This problem is forcing the aircrew to either forego wearing an existing chemical protective hood under the helmet or to remove structural components inside of the helmet in order to achieve a comfortable fit. Either scenario represents a serious risk to flight safety in any NBC training or operational environments. The present SPH5-CF helmet shell illustrated in FIG. 1 and identified by the number 10 is a nylon, graphite and fibreglass cloth composition with black rubber edge beading. Components located inside of the helmet shell 10 include an energy absorbing liner 12 (see FIG. 2) to absorb and reduce impact forces and a pre-formed thermoplastic liner (TPL) 14 that sits inside the energy absorbing liner 12. The energy absorbing liner 12 is formed from rigid foamed white polystyrene plastic and is moulded to conform to the contour of the shell's inner surface. Hook fastener tabs on the outside surface of the liner mate with pile fastener on the inside of the shell 10 to secure the liner in place. Hook fastener tabs on the inside surface of the liner secure the TPL 14 to the energy absorbing liner 12. The pre-formed TPL 14 provides a comfortable inner helmet which can be custom fit to an individual head size. It consists of a plastic layer assembly and a removable, washable cloth cover. The TPL cloth cover is an air permeable black fabric featuring sides made of pile material to allow attachment to the hook fastener tabs on the energy absorbing liner 12. The TPL is pre-formed in three sizes and can be custom fitted by removing any of the eight separate layers of plastic from the TPL.

[0020] It was found in one study that while one size of helmet should provide an acceptable fit, this was not the case when worn with or without a chemical protective (CP) hood for use in a NBC threat environment and all operational scenarios. The existing multi-layered hoods 18 shown in FIG. 4 when worn over the head harness 16′ of the AC4 respirator 16 shown in FIG. 3 led to an unacceptable fit due to the excess bulk. The multi-layered hood 18 shown in FIG. 4 is a dual-layer air-permeable hood composed of a thick inner charcoal-impregnated fabric layer for vapour protection and an outer liquid-repellent and flame-retardant Kermel (trade-mark) fabric layer. The hood has a front opening with edges that surround and fit against the facepiece of the respirator. The assembly of the respirator 16, hood 18 and helmet 10 is illustrated in FIG. 5. In one study, out of 15 aircrew, 80% would need a larger size helmet to operate with chemical defence headgear while 20% would require modification to the TPL 14 of the SPH5 helmet. In another study, 75% of the subjects using a SPH5 helmet could not don their helmets over the respirator and hood. Modifying the TPL or issuing two sizes of helmets is possible but an expensive alternative and would not be feasible for those requiring larger size helmets. An alternative would be to use a polymer hood 19 as illustrated in FIG. 6 rather than a multi-layered hood. The polymer hoods are thin but, however, impose an undue thermal burden and offers a poor seal with respirators such as the AC4.

[0021] An integrated hood according to the present invention provides a solution to the above-mentioned problems in that it is thin enough above the respirator not to compromise the fit underneath the helmet and, it also provides chemical protection to the pilots without compromising the protection and functions of the helmets. The low burden integrated chemical protective hood 20 according to the present invention is illustrated in FIG. 7 where 7(A) is a front view of hood 20 assembled over a respirator 16, 7(B) being a side view and 7(C) a back view of the assembly. The hood 20 is composed of two portions, a multi-layer lower skirt portion 22 similar to the bottom of hood 18 in FIG. 4 and a thin layer top portion 24 which is configured to match the curved surface area of the thermoplastic liner (TPL) inside the aircrew helmet. In the integrated hood 20, the main body skirt portion 22 of the hood 20 is constructed of a single or multi-layered filter barrier material while the area underneath the helmet, i.e. under the TPL in a SPH5 helmet, is formed of a thin single layer 24. In one embodiment of the invention, the portion of the hood that fits under the TPL is formed as a mesh, e.g. a polyester mesh 24, as shown in FIGS. 7A, B and C to minimize the bulk wherever there is contact with helmet and to minimize any heat stress. In this embodiment, the area that is married to the helmet needs to be suitably sized in order to prevent toxic vapours from reaching the skin of the users. In a second embodiment of the invention, the thin single layer 24 is formed of thin single layer of activated carbon impregnated filter material such as carbon impregnated lycra which would maintain some vapour protection in that area of the hood. When a mesh layer 24 is used, the mesh portion should be perfectly matched with the outer edges of the TPL so that the filter material provides optimum protection in areas where the helmet may not be fitted tightly to the head. The thin single layer may be made of woven, knit or non-woven material. The integrated hood 20 provides a proper and comfortable fit for the user, does not compromise the impact protection of the helmet or impose an undue heat load in the head area.

[0022] Three modifications of the low burden integrated chemical protective hood was trialled for user acceptability in a study conducted in November 2000. All three were satisfactory for comfort and fit when worn over the CF AC4 and under the SPH5-CF helmet. The new hoods designed according to the present invention were found to provide an improved fit over the current in-service aircrew chemical protective hoods.

[0023] The Protective Factors (PF) of a CP lightweight hood and CP polymer hood, measured on a head form at various regions in a controlled environmental chamber using a chemical agent stimulant vapour are shown in FIG. 8. The PFs for a new light-weight chemical protective hood with a polyester mesh portion under the TPL typically ranged between 1000 and 10000+ over the majority of the regions of the head. A PF of 50000 was obtained at the top scalp which essentially reflects a complete absence of chemical vapour in this region and is the result of the extremely tight fit achieved between the thermoplastic liner and the thin mesh layer of the hood at this location. Therefore, this hood provides very good protection without the use of carbon absorbent at locations where equipment interfaces tightly with the body. The thin mesh layer, at the same time, permits the helmet to be used without removing any structural components from the liner to achieve a safe comfortable fit.

[0024] The measured PFs determined for a chemical protective polymer hood were, in sharp contrast to the integrated hood, generally less than 100 over all regions of the head with the exception of the top scalp, right ear and under the respirator. The measured PFs for the polymer hood are shown in FIG. 8 where they can be compared with the PFs obtained for the integrated hood. The polymer hood, based on the results of the measured PFs, offers between 10 and 100 times less chemical vapour protection than the new light-weight chemical protective hood over most regions of the head. It should be noted that the dosage used in the vapour test on the polymer hood was one half that of the dosage used for the tests on the other hood. It is strongly suspected that the protection afforded by hoods that contain no carbon absorbent may be concentration-time dependent, i.e. the longer that it is worn or the higher the vapour concentration during an exposure, the lower the protection to the user.

[0025] The measured PFs shown in FIG. 8 clearly show that the chemical protective hood according to one embodiment of the present invention provides superior vapour protection compared to a typical polymer hood. In addition, this new light-weight chemical protective hood concept offers improved fit and comfort with the potential for a significant reduced thermal burden when compared to a 100% polymer hood.

[0026] Various modifications may be made to the preferred embodiments without departing from the spirit and scope of the invention as defined in the appended claims. The top portion and a layer of the skirt portion, for instance, may be formed of a single layer, permeable, highly absorbent chemical protective carbon barrier material. An ultra-thin insert at the top of hood that is configured to match the curved surface area of the thermoplastic liner inside the aircrew helmet may be used in other versions.