| A filter mask provides protection to the
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| | reaction may take place, it is not
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| wearer from harmful airborne substances
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| | necessary; the method may work by
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| and usually covers only the mouth and
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| | attractive charges (for example, if the
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| nose. It limits the course of air so that
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| | target particles are positively charged,
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| it must flow through a filter which
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| | use a negatively charged substrate).
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| removes harmful dusts or toxic gases.
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| | Examples of substrates include activated
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| Such masks range from cheaper,
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| | carbon, and zeolites. This effect can be
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| single-use, disposable types to reusable
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| | very simple and highly effective, for
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| models with replaceable cartridges.
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| | example using a damp cloth to cover the
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| Because of their simple, passive design
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| | mouth and nose whilst escaping a fire.
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| they are most commonly used for
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| | Gas masks used in World War One were made
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| filtration of tiny suspended solid or
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| | as a result of poison gas attacks that
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| liquid particles and often referred to as
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| | took the Allies in the trenches on the
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| particulate masks. For this purpose, they
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| | Western Front by surprise. Early gas
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| usually employ a dense, fine natural or
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| | masks were crude as would be expected as
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| synthetic fiber mesh. To aid particulate
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| | no-one had thought that poison gas would
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| filtration, the mesh is sometimes coated
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| | ever be used in warfare as the mere
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| with substances that enhance the tendency
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| | thought seemed too shocking.
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| of particulates to adhere to the fibers.
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| | Most of the harmful vapours and smoke
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| For gas filtration, mask cartridges are
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| | will be dissolved in the water on the
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| filled with activated carbon or certain
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| | cloth, giving you vital extra seconds to
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| resins that will absorb substances such
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| | escape.
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| as volatile organic compounds (VOCs),
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| | This principle relies upon the fact that
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| eliminating them from the air breathed.
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| | substances that can do harm to humans are
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| Though less effective for this purpose,
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| | usually more reactive than air. This
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| and only suitable to the least demanding
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| | method of separation will use some form
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| applications, single-use masks also
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| | of generally reactive substance (for
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| sometimes employ embedded carbon granules
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| | example an acid) coating or supported by
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| in the fiber mesh. There are different
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| | some solid material. An excellent example
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| cartridges for different compounds. When
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| | is resins. These can be created with
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| filter cartridges become saturated or
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| | different groups of atoms (usually called
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| particulate accumulation within them
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| | functional groups) that exhibit different
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| begins to restrict air flow, they must be
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| | properties. Thus a resin can be tailored
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| changed.
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| | to a particular toxic group. When the
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| A gas mask is a mask worn on the face to
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| | reactive substance comes in contact with
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| protect the body from airborne pollutants
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| | the resin, it will bond to it, removing
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| and toxic materials. The mask forms a
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| | it from the air stream. It may also
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| sealed cover over the nose and mouth, but
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| | exchange with a more harmless substance
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| may also cover the eyes and other
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| | at this site.
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| vulnerable soft tissues of the face. Some
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| | Though it was crude, the hypo helmet was
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| gas masks are also respirators, though
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| | a sign to British troops in the trenches
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| the word gas mask is often used to refer
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| | that something was being done to help
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| to military equipment (e.g. Field
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| | them during a gas attack and that they
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| Protective Mask, etc.)
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| | were not being left out for slaughter. As
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| Airborne toxic materials may be gaseous
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| | the months passed and the use of poison
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| (for example the chlorine gas used in
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| | gas occurred more frequently, more
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| World War I) or particulate (such as many
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| | sophisticated masks were developed and
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| biological agents developed for weapons
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| | introduced.
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| such as bacteria, viruses and toxins).
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| | There are two main difficulties with
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| Many gas masks include protection from
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| | gas-mask design:
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| both types. Unlike other breathing
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| | The user may be exposed to many different
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| devices, gas masks do not require the
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| | types of toxic material. Military
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| user to carry an air supply as in the use
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| | personnel are especially prone to being
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| of scuba gear. However, this means that
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| | exposed to a diverse range of toxic
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| the wearer depends on the air in the
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| | gases. However if the mask is for a
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| atmosphere, the same medium of the toxic
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| | particular use (such as the protection
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| materials. Thus, the mask must remove
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| | from a specific toxic material in a
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| them and relay clean air to the wearer.
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| | factory), then the design can be much
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| There are three main ways of achieving
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| | simpler and the cost lower.
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| this: filtration, absorption and
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| | The protection will wear off over time.
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| adsorption, and reaction and exchange.
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| | Filters will clog up, substrates for
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| Absorption is the process of being drawn
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| | absorption will fill up, and reactive
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| into a (usually larger) body, or
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| | filters will run out of reactive
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| substrate, and adsorption is the process
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| | substance. This means that the user only
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| of deposition upon a surface. This can be
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| | has protection for so long, and then they
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| used to remove both particulate and
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| | must either replace the filter device in
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| gaseous hazards. Although some form of
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| | the mask, or use a new mask.
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