Xcaper Filter Abstract

The Xcaper Smoke Mask works by trapping gaseous and particulate contaminants (often referred to as aerosols by smoke researchers) within a filtering medium similar to the "packed bed" filters commonly used in the chemical processing industry. Many such so-called mechanical filters, which do not rely on chemically reactive or catalytic components, are in widespread use in hazardous chemical and industrial environments; their efficiencies can approach 100%.

They are often used to purify air by filtering out not only dusts and mists but also organic and acid gases such as carbon monoxide, carbon dioxide, hydrogen chloride, and many others.

Many varieties of mechanical filter type purifying masks are available through industrial and laboratory safety supply houses. Several have been tested and investigated by NIOSH and other organizations for both filtering efficiency and tightness of fit. Vendors who market such personal respiratory devices through established industrial safety supply outlets publish performance data that suggests that these masks can be very effective filtering devices, indeed, when used within their prescribed limits.

Claims have been made that higher filtering efficiencies can often be achieved with "chemical" filters, those that rely on transformation of harmful contaminants by involving them in a chemical reaction as they pass through the filter medium. The reaction changes the chemical nature of the contaminant to something harmless (usually a relatively inert solid which remains trapped within the filter). This type of filter, however, must be chosen for a specific toxic species or a very limited range of species, as the reaction mechanism is tailored to a particular type of substance.

Since smoke from fires is a complex mix of particles, liquid droplets, gases, and sticky agglomerated mixtures of all three, chemically reactive filtering media, regardless of sophistication, cannot be expected to provide sufficient protection for all of the products of combustion which may be a threat to life-safety. As reactive media fill up with trapped particulates and the residues of reacted products, they become markedly less efficient. Breathing through them also becomes more difficult as the partially blocked air passageways produce a large pressure drop, which the wearer must overcome by breathing through the filter with more force. Chemically reactive filters also generate considerable heat through the chemical reaction mechanism, causing the breathable air to become in many cases too hot. The purported advantages of high capture and retention efficiencies of such filters, therefore, would not be borne out in most real fire situations.

Unlike chemical filters, the Xcaper filter can act effectively on a wide range of substances and actually become more efficient with use, as the trapped contaminants act to further obstruct the path of newly entering contaminants. The air passageways remain relatively free of obstruction since the filter acts primarily by adsorbing contaminants onto electrochemically active surfaces of otherwise inert filter material. No additional reaction products are created, and the adsorbed material is effectively removed from further interference with the passing stream. Adsorption continues even with particulate build-up because the micro scale electrochemical activity continues unabated. The growing quantity of adsorbed material acts only to further slow the passage of the coagulation aerosols, providing more "residence" time for the capture to take place. The filter, thus, becomes more efficient over time. Saturation will be approached but only very slowly and, as field tests have shown, the time to saturation is much greater than the time of anticipated use.