9 GAS SENSORS FOR MEASURING GAS CONCENTRATION; GAS DETECTORS FOR DETECTING THE PRESENCE OF GAS; SELF-RESCUE APPARATUS AND INSTRUMENTS, NAMELY, RESPIRATORY GAS CONTAINERS, OXYGEN BREATHING UNITS, RESPIRATORY BREATHING UNITS AND SELF-CONTAINED BREATHING UNITS; ONBOARD AIRCRAFT OXYGEN SOURCES FOR BREATHING SUPPORT; RESPIRATORY MASKS; FILTERS FOR RESPIRATORY MASKS; BREATHING APPARATUS FOR DIVERS, NAMELY, REBREATHERS AND ACCESSORIES THEREFOR, NAMELY, COMPRESSED AIR BAILOUT UNITS, SODA LIME CARTRIDGES AND BUOYANCY BLADDERS