(a) Removal of respirators.--Anti-gas fans should be used to assist in clearing the trenches of gas, so as to admit of respirators being removed. Respirators and helmets must not be removed until permission has been given by the Company Commander. A sharp look out must be kept for a repetition of the gas attack, as long as the wind continues in a dangerous quarter. 2. MOVEMENT: Owing to the enemy gas sometimes causing bad after effects, which are intensified by subsequent exertion, the following points should be attended to: (a) No man suffering from the effects of gas, however slightly, should be allowed to walk to the dressing station. (b) The clearing of the trenches and dugouts should not be carried out by men who have been affected by the gas. (c) After a gas attack, troops in the front trenches should be relieved of all fatigue and carrying work for 24 hours by sending up working parties from companies in rear. (d) Horses which have been exposed to the gas should not be worked for 24 hours if it can be avoided. 3. CLEARING DUGOUTS AND OTHER SHELTERS: It is essential that no dugout be entered after a gas attack event with box respirators or helmets adjusted, until it has been ascertained that it is free from gas. The only efficient method of clearing dugouts from gas is by thorough ventilation. The older method of spraying is not efficient. An appreciable quantity of gas may be retained in the clothing of men exposed to gas attacks and also in bedding, coats, etc., left in shelters. Precaution should, therefore, be taken to air all clothing. 4. VENTILATION: _Natural Ventilation_.--Unless a shelter has been thoroughly ventilated by artificial means, as described below, it must not be slept in or occupied without wearing respirators, until at least 12 hours after a gas attack. It must not be entered at all without respirators on for at least 3 hours. The above refers to cloud gas attacks. In the case of gas shell bombardments the times cannot be definitely stated, as they depend on the nature of the gas used and the severity of the bombardment. With lachrymatory gases the times after which shelters can be used without discomfort may be considerably longer than those mentioned above. _Ventilation by Fire_.--All kinds of shelters can be efficiently and rapidly cleared of gas by the use of fires. Shelters with two openings are the easiest to ventilate and where possible, dugouts with only one entrance should have a second opening made, even a very small one, to assist in ventilation. In dugouts provided with a single exit at the end of a short passage, the best results are obtained if the fire is placed in the center of the floor of the dugout and at a height of about 9 inches.