| http://www.w3.org/ns/prov#value | - A device for testing the tightness of fit of a gas mask which has a tubular respiratory air inlet and a tubular exhaling air outlet, which is applied over the face of a wearer, comprises a bag-like headpiece which is engageable over the wearer's head and is preferably made of a transparent material, such as plastic, and which is provided with an opening for the wearer's neck and an opening for the
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