In instances where work is performed in a contaminated environment by workers wearing respirators, the workers typically exit the contaminated area by passing through one or more cleanup areas or decontamination zones. Often the workers continue to wear their respirators in the cleanup areas. This practice, however, presents the risk that contaminated matter, drawn into the filter of the respirator during use, may fall out of the filter and into the cleanup area, or even into the clean environment beyond the cleanup area. Heretofore, to avoid this problem, wearers of such respirators would sometimes plug up or tape up the filter to prevent contaminants from falling out. In doing this, however, the worker blocked the air flow through the filter whereby the worker could no longer use the respirator. As a result, the worker would have to remove the respirator at an earlier point in the decontamination process than would otherwise be desirable. Alternatively, the worker would, after plugging up the filter, have to hold his breath until he was sufficiently decontaminated to safely remove the respirator.
U.S. Pat. Nos. 4,548,626 and 4,543,112 each describe a respirator assembly including a respirator filter having a one-way valve permanently attached to the intake of the filter, the valve being operable to permit ingress of inhaled air and prevent discharge of exhaled air therethrough. Both of these cover assemblies effectively perform their intended functions, i.e., permitting respiration while preventing contaminated material from falling from the respirator filter during decontamination of the worker. With such a construction, however, resistance to air flow through the respirator filter is increased by virtue of the energy required to open the one-way valve upon each inhalation.
It is also known, as described in U.S. Pat. No. 4,850,346, to provide at least one valve fitting in a respirator face mask wherein the valve fitting includes a one-way valve and is specifically constructed and arranged to detachably receive the outlet of a respirator filter. Hence, if the mask is to be used, a respirator filter must be secured to the mask via the valve fitting. As a result, at all times during use the wearer must overcome not only the inherent air resistance of the filter material but also that of the one-way valve supported in the face mask.
U.S. Pat. Nos. 5,036,844 and 5,033,507 show removable cover assemblies for respirator filters, the former having a one-way valve permanently mounted in the cover while the latter has no such valve. While both of these filter assemblies enable the filter to easily be replaced by removing the cover, the '507 patent always has the one-way valve in the air flow path during use.
An advantage exists, therefore, for a respirator apparatus which simultaneously is lightweight, provides no additional air flow resistance in excess of that of the respirator filter material during normal usage conditions, and, during worker decontamination situations, permits respiration to continue while effectively preventing contaminated material from falling from the filter.