"Gas Masks: Have charcoal filters and in a nerve, or blood agent chemical contaminated environment; filters must be changed every 45 mins. You will also need several suits lined with charcoal and those too must be changed commonly known as a MOPP exchange.
This must be done in a safe controlled location. Also you must consume large amounts of water while wearing the suits due the elevated body heat. You will also need to seal all openings to the suit around the wrists, waist and ankles. You must have a chemicals hood attached to the Mask you fully cover and seal your head and neck and tape sealed the opening of the hood to the suit to prevent liquid and gas contamination.
Their are designated filters for the mask that work with tear gas and nerve/blood agents. Unless you meet the above standard all you have is a false sense of security." ~Daniel W. Shrigley