Description: Two men are filmed on a suburban street (possibly in Willesden) wearing protective rubber uniforms. One man is taping up the others gloves and sleeves to seal the suit. The taped up man dressed in his protective gear and gas mask walks to a damp patch on the road and swabs the liquid with cotton wool, which he places in a glass jar, seals and takes back to the other man. The bottle is placed in a metal canister. An on-screen title reads 'a sample of liquid gas is collected for transmission to the senior Gas Adviser, if required'. Elsewhere, at a table, the metal canister is opened and a glass jar marked with the number 2 is removed and examined. A man in a gas mask and uniform is shown filling out a form. Title: 'The G.I.O. writes his report and informs the Incident Officer of his findings. The Assistant telephones control.' There is a close-up of the form but it is not legible. Some men in protective gear are filmed leaving a roped off site in a suburban area. Another title reads 'By Permission of the Senior Gas Advisers, method of decontamination is shown under conditions in which real mustard gas could be used.' Title: 'The Decontamination Squad arrive.' The decontamination squad unload a truck and place a boot decontamination tray containing bleach powder on the road. They open large metal canisters of decontamination chemicals. Title: 'The limits of contamination are marked by a trail of bleach powder.' Title: 'Decontamination in progress.' The men in protective outfits, spade bleach powder from a wheel barrow and brush it out on to a road. Title: 'Note how the liquid mustard gas inflames on contact with bleach powder.' Title: 'Each man passes through the bleach tray to avoid spreading contamination.' The Warden is filmed walking down a suburban street. Title: 'The following scenes show the use of the POCKET VAPOUR DETECTOR. This is used by Wardens only on instructions from Control, if no G.I.O. is available.' The Warden places his gas mask on, and shakes a rattle in alarm. Elsewhere, some men are filmed marching in a yard. Title: 'This yard is used for loading and unloading lorries engaged in important work and the building is also used by the Home Guard.' Title: 'The problem here is whether loading and unloading can take place in safety and if it is safe for the Home Guard to carry on without anti-gas precautions.' The wardens have sealed off a suburban area with barricades and a sign reading 'danger gas'. Title: 'Message from Control: - No G.I.O. available. Blister gas confirmed in your Division. Determine vapour concentration in yard.' Title: 'The Detector must be prepared by the Warden BEFORE going to the incident.' There is a close-up of the preparation of a pocket vapour detector. A title reads: 'Note different method of spotting.' A female warden is filmed walking out. Title: 'The Warden approaches from up-wind.' She reaches the bar barrier, places her gas mask on and walks on. Title: 'Preliminary test without GUARD TUBE.' The Warden tests the air with a pocket detector. Title: 'The Congo Red Paper has blued all over, suggesting GAS PRESENT.' Title: 'The test is repeated with Guard Tube, which only allows MUSTARD GAS to pass. This is repeated in several positions and an average reading computed.' The female warden performs another test. The filmed ends with a shot of a chart showing the safe time of exposure to varying amounts of mustard gas vapour (it appears to be dated 8/43).