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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
SPONTANEOUS IGNITION OF HYDROGEN
Late one evening in a chemical engineering facility, a student employee was working near a six-cylinder hydrogen gas manifold when she heard a cracking sound above her, followed by a whistling sound. She stepped away from the cylinder area to where she could see above the roof and noticed a flame on the roof above the cylinders. She immediately reported this to her supervisor, who went up on the roof and found that a rupture disk on the hydrogen manifold had ruptured. Had the disk ruptured in the daylight, the flame might not have been visible. The most likely cause of the flame was the spontaneous ignition of the hydrogen as it entered the air at high pressure. The hydrogen manifold was shut down, the rupture disk was replaced, and research was resumed.
the indicated action can be taken without exposing personnel to highly toxic substances. The leaking cylinder can be moved through populated portions of the building, if necessary, by placing a plastic bag, rubber shroud, or similar device over the top and taping it (preferably with duct tape) to the cylinder to confine the leaking gas. If there is any risk of exposure, the environmental health and safety office should be called and the area evacuated before the tank is moved.
If a leak at the cylinder valve handle cannot be remedied by tightening a valve gland or a packing nut, emergency action should be taken and the supplier should be notified. Laboratory workers should never attempt to repair a leak at the junction of the cylinder valve and the cylinder or at the safety device; rather, they should consult with the supplier for instructions.
When the nature of the leaking gas or the size of the leak constitutes a more serious hazard, a self-contained breathing apparatus and protective apparel may be required, and personnel may need to be evacuated (see Chapter 5, section 5.C.2). Cylinders leaking toxic gases always require protective equipment and evacuation of personnel. Cylinder coffins are also available to encapsulate leaking cylinders. (See Chapter 5, section 5.G, for more information.)
Pressure regulators are strongly recommended to reduce a high-pressure supplied gas to a desirable lower pressure and to maintain a satisfactory delivery pressure and flow level for the required operating conditions. They can be obtained to fit many operating conditions over a range of supply and delivery pressures, flow capacities, and construction materials. All regulators are of a diaphragm type and are spring-loaded or gas-loaded, depending on pressure requirements. They can be single-stage or two-stage. Under no circumstances should oil or grease be used on regulator valves or cylinder valves because these substances may be reactive with some gases (e.g., oxygen).
Each regulator is supplied with a specific CGA standard inlet connection to fit the outlet connection on the cylinder valve for the particular gas. Regulators should be checked before use to be sure they are free of foreign objects and correct for the particular gas.
Regulators for use with noncorrosive gases are usually made of brass. Special regulators made of corrosion-resistant materials can be obtained for use with such gases as ammonia, boron trifluoride, chlorine, hydrogen chloride, hydrogen sulfide, and sulfur dioxide. Because of freeze-up and corrosion problems, regulators used with carbon dioxide gas must have special internal design features and be made of special materials. Regulators used with oxidizing agents must be cleaned specially to avoid the possibility of an explosion on contact of the gas with any reducing agent or oil left from the cleaning process.
All pressure regulators should be equipped with spring-loaded pressure-relief valves (see section 6.D.2.2.1 for further information on pressure-relief devices) to protect the low-pressure side. When used on cylinders of flammable, toxic, or otherwise hazardous gases, the relief valve should be vented to a hood or other safe location. The use of internal-bleed-type regulators should be avoided. Regulators should be removed from corrosive gases immediately after use and flushed with dry air or nitrogen. Mercury bubblers should not be used.
It is important to keep all sources of ignition away from cylinders of flammable gases and to ensure that these cylinders will not leak. A solution of soapy water should be used to detect leaks except during freezing weather, when a 50% glycerin-water solution or its equivalent should be used. Connections to piping, regulators, and other appliances should always be kept tight to prevent leakage, and the tubing or hoses used should be kept in good condition. Regulators, hoses, and other appliances used with cylinders of flammable gases should not be interchanged with similar equipment intended for use with other gases. Cylinders should be grounded properly to prevent static electricity buildup, especially in very cold or dry environ-