_a. Handling._ Handle all cylinders and flame throwers carefully; never drop them and never subject them to shocks or blows. Keep valve-protection caps secured when cylinders are being handled, except when such handling is incident to the use of the nitrogen or air. _b. Storage._ Keep all cylinders and charged flame throwers or tank groups (Par 77) in open or closed storage. They must, however, be protected from dampness and excessive rise in temperature caused by the direct rays of the sun or other source of heat. Avoid storing them near highly flammable substances, or in places where they may be struck by moving objects. Segregate empty cylinders to avoid confusion. _c. Personnel._ Do not attempt to use compressed gases unless trained in this work. Use gases only for the purposes for which they are intended. _d. Cylinder valves._ Do not tamper with safety devices in cylinder valves. If available, use the proper replacement parts for safety devices which are in need of repair. If such parts are not available, do not attempt to use makeshifts or nonstandard parts. _e. Opening of valves._ Open valves slowly and fully each time nitrogen or compressed air is transferred from a cylinder. When a wrench is used, be sure it is one that fits properly, and that it is kept ready for instant use while the compressed gas is being released. _f. Threads._ See that threads match before making connections. Some valves are provided with special threads which must be matched by the threads in the equipment being connected. _g. Correct equipment._ Use gages, regulators, hose, pipe, and tubing of the type manufactured or specified for the particular apparatus or compressed gas. _h. Repair._ Never attempt to alter or repair a cylinder. _i. Flames and sparks._ Do not permit flames, sparks, or ignition from the flame thrower or other source to touch hose. _j. Blowing out dust._ Immediately before coupling an attachment to the pressure tank or cylinder valve, open it for an instant to blow out any dust or dirt. Never stand where gas or dirt may be blown into the eyes or face. If the valve is difficult to open, apply more force gradually. _k. Special devices._ Do not attempt to use any special connections or equipment without the approval of a qualified expert. _l. Keeping valves closed._ Keep the valve of each cylinder closed when its contents are not actually being released from or admitted to the cylinder. This applies alike to all cylinders, whether they contain a compressed gas or are empty. 34. CHARACTERISTICS OF FUELS.