A air gas detection pack is provided. The air gas detection pack has a card receiving pocket which slidably receives a gas detection card, the gas detection card having a plurality of chemically reactive materials retained therein and exposed to outside air through a plurality of aligned air permeable apertures formed in the front and rear wall of the substance detection pack. The combined gas detection card and gas detection pack indicates the concentrations of gases in the air. The air permeable apertures in conjunction with the reactive materials of the substance detection card are covered with a filtering media to protect the reactive material from dirt and dust contamination.