Colorimetric gas dosimeter

Claim 1

A gas dosimeter comprising: a housing having a flat back wall with an inner surface, a flat front wall parallel to and spaced from said back wall, said front wall having an inner surface, and a side wall connected between said back and front walls, said side wall having an inner surface, said front, back and side walls together defining an enclosed measuring chamber for receiving a gas to be measured, said chamber having a thickness between said inner surfaces of said back and front walls which is small compared to a dimension of said chamber which is parallel to said front and back walls so that said chamber has a flat configuration; a color indicator disc capable of reacting with a gas and as a result thereof changing state which can be perceived, said disc being connected to said back wall engaged against said inner surface of said back wall; and an inlet pipe section connected to said front wall and extending out of said front wall, said pipe section having an inside and outside diameter, said front wall having an opening communicating with the exterior of said pipe section and having a diameter substantially equal to the outside diameter of said pipe section, the inside diameter of said pipe section being selected to be less than five times the dimension of said chamber extending parallel to said front and back walls, the length of said pipe section taken in a direction perpendicular to said front wall being selected to be less than the thickness of said chamber, said length of said pipe section being at least long enough to form a diffusion area so that a mass transport of gas entering into said chamber through said pipe section takes place so that said mass transport of gas is largely independent of air currents outside of said chamber, said pipe section being centrally located in said front wall, one portion of said inlet pipe sections extending out of said chamber and a second portion of said inlet pipe section extending into said chamber thereby directing the gas entering said chamber initially towards the center of said indicator disc, whereby the reaction takes place at a center of said indicator disc and propagates radially outwardly from the center of the indicator disc along the indicator.