The Xcaper filter is a new type of smoke filtering device claiming a very high level of efficiency in filtering out the toxins and particulate products of combustion from common fires. A professional fire protection device called WHIFFS®, Wilfire Hazardous Inhalation Firefighters' Filtration System, holds an Xcaper filter in a protective Nomex® shroud that is worn over the nose and mouth and allows the wearer to breathe normally, maintain a clear line of vision, and keep both hands free.

The functional aspects of the filtering process are complex. They are dependent on details of the filter's construction as well as on the physical and environmental conditions of use. Among the most readily identifiable mechanisms are the following:

As a rather densely packed collection of small plastic beads in a contained natural gel bath, the filter behaves most fundamentally as a simple physical absorption device, utilizing a large enclosed volume for 'storage' of breath-entrained combustion particulate matter.
The active thickness of the filter offers substantial interference with the path of smoke particulates drawn in through the normal breathing process. Given the internal packing structure of fine beads and relatively small void fraction it is clear, even without quantification of the effect, that the mean travel distance (mean path length) of a smoke particle from outer to inner surface of the filter would be several times the direct linear thickness of the filter. As interstitial spaces (between the beads) fill with trapped particulates, mean path lengths would increase far more, delaying arrival of particulates at the inner surface.

Over the course of active travel of combustion particulates, well known "aging" effects alter both their character and behavior. This widely observed phenomenon, generally termed coagulation, describes the agglomeration and coalescing behavior of gaseous, liquid, small solid and aerosol products into much larger masses whose number and size vary in a complex manner with both time and ambient temperature. Coagulation traps large numbers of toxic gas molecules within the clotted mass, the effect being enhanced by longer residence times and cooler temperatures.
The physical structure of a smoke particulate may be thought of as characterized by a large surface area and a variable surface electric charge resulting from the polar structures of its constituent molecules. Polar charges of the far smaller molecules of the remaining free gaseous combustion products will eventually cause electrochemical adsorption of the gases onto the surfaces of the particulates. Due to the very large-scale difference between a gas molecule and even the smallest of particulates, it is likely that thousands of gas molecules can adhere to the surface of a single particulate given sufficient residence time for adsorption to occur.
Most common gases, especially those typically found as combustion by-products, are soluble in water and other solvents and natural gels. Free gases not yet trapped by aerosol formation or by adsorption/coagulation processes are subject to secondary entrapment through dissociation in a solvent gel.
Still other mechanisms may be of importance, particularly as they affect the movement of ionic or surface charged species through the filter. Among these are electrolytic solution tension effects (i.e., Helmholtz double layer effects), electrophoretic effects, and potential equilibrium altering gas-solvent reactions. Such "secondary" mechanisms could be considered insignificant, but the exceedingly long reaction residence times characteristic of this type of filter may lead to enhanced effects which would not normally be expected.

SUMMARY

In view of the major roles played by such processes as adsorption, aerosol formation and coagulation in typical fire and smoke aging processes, it is likely that these mechanisms, along with the added effects of absorption, interference and solvent-induced dissociation, are also important in accounting for the observed performance of the Xcaper filter. It is also possible that other mechanisms related to microscale details of the electrochemical environment within the filter can be identified as possible contributors.