FIELD OF THE INVENTION
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The present invention relates to a protective hood to
be worn over a respirator when used in hazardous environments
such as those where nuclear, chemical and biological agents may
exist and, in particular, to a hood that is positionable over
respirators when used with aircrew flight helmets.
BACKGROUND OF THE INVENTION
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In hazardous environments where toxic chemicals might
exist or where nuclear, biological and chemical (NBC) agents
may be present (or expected) personnel must wear protective
clothing and respirators, in addition to their regular
equipment, to protect themselves from those type of agents.
For personnel who require helmets or headgear, such as aircrew,
the protective clothing must not impair the intended function
of the headgear. The helmet that is worn by aircrew has
several functions that must be maintained, even during NBC
operations. These functions include, for instance, protection
of the head in the event of a crash, protection of ears against
excessive noise and the provision of means for electronic
communications. If a protective hood is to be worn under the
headgear, then it must not cause discomfort to the wearer, or
at least minimize any discomfort, and it must maintain the
functions of the headgear to an acceptable level.
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An incompatibility problem involving the present in-service
aircrew chemical protective hood and aircrew flight
helmets exists. This problem is forcing the aircrew to either
forgo wearing the existing chemical protective hood or remove
structural components inside the helmet to achieve a
comfortable fit. Either scenario represents a serious risk to
flight safety in any training or operational environment.
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Chemical protective (CP) hoods that are presently
available are made from multiple layers of materials or from
polymers. Multiple layer CP hoods are described in Canadian
Patent Application 2,027,850 that was filed on
October 17, 1990. These multi-layered hoods are thick and
cannot be worn underneath aircrew helmets, such as a SPH5-CF
helmet, without requiring some modification to the helmet.
Layers in the Thermal Plastic Liner (TPL) in the SPH5-CF helmet
or in some cases the entire impact protective layers need to be
removed to enable the donning of this helmet over a multi-layered
chemical protective hood. One alternative would be to
don a thinner rubber hood. The rubber hoods would, however,
impose an undue thermal stress on users in hot climates or in
heated aircrafts.
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Thin air impermeable polymer hoods and multi-layered
filter barrier hoods are two types which are currently
available. The polymer hoods are thin but impose an undue
thermal burden on users. The seams of these polymer hoods are
rigid and may cause hot spots or stress points underneath the
hood and, furthermore, they offer a poor seal with respirators
such as the Canadian Forces (CF) AC4. The multi-layered filter
barrier hoods such as the CF in-service hoods are made from a
thick barrier layer and separate outer layer sewn separately.
This causes extra bulk in seam areas and can only be worn if
TPL layers are removed from the SPH5 helmet which would
compromise the impact safety and the head protection provided
by this helmet.
SUMMARY OF THE INVENTION
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It is an object of the present invention to provide a
chemical protective hood that can be worn under an aircrew
flight helmet without imposing an undue thermal burden on users
or requiring modification to be made to that helmet.
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A chemical protective hood to be worn over a
respirator in a manner such that it is located between a helmet
and the respirator, according to the
invention, comprises a skirt portion of filter barrier material
containing an opening with edges configured to surround and fit
against a respirator's facepiece,a top portion of the hood
being formed of a thin single layer that fits under a
helmet, the thin single layer being configured to match the
curved inner surface of the helmet.
DESCRIPTION OF THE DRAWINGS
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Embodiments of the present invention will now be
described in more detail with reference to the accompanying
drawings, in which:
- Fig. 1 is a drawing of a known helmet, the SPH5-CF
helmet,
- Fig. 2 are drawings that illustrate the thermoplastic
liner and the energy absorbing liner for the SPH5-CF helmet,
- Fig. 3 is a drawing that illustrates the head harness
of an AC4 respirator,
- Fig. 4 is a drawing that illustrates a known multi-layer
hood located over an AC4 respirator,
- Fig. 5 shows the SPH5-CF helmet with a multi-layer
hood and AC4 respirator assembled,
- Fig. 6 shows a known polymer hood assembled over an
AC4 respirator,
- Fig. 7(A), (B) and (C) show, respectively, a front
view, a side view and a back view of a hood according to the
present invention assembled over an AC4 respirator, and
- Fig. 8 contains a graph illustrating the Protection
Factors (PF's) measured on a head form for the low burden
integrated protective hood according to the present invention
and a graph that shows the measured PF's for a M45 polymer hood
when used with AC4 respirators and the SPH5-CF helmet.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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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.
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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
forgo 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.
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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 offer a poor seal with respirators
such as the AC4.
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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 Fig. 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.
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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.
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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.
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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.
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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.
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Various modifications may be made to the preferred
embodiments without departing from the 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.