By securing with wooden saddles and a steel band, 12 cylinders can be lifted as a unit
H. F. REINHARD Union Carbide Corp., New York, N.
Y.
F. R. FETHERSTON Compressed Gas Association, New York, N.
Y.
Safe Practices for Handling Compressed Gases When compressed gases cause an accident someone has probably been careless or negligent
F o u m m s O F THE compressed gas industry and those responsible for its growth have set high standards for storage, handling, and use of compressed gases and design of associated equipment. This safety work will continue to receive utmost attention. For this discussion, the definition of a compressed gas given by the Interstate Commerce Commission (ICC) is used : "Any material or mixture having in the container either a n absolute pressure exceeding 40 pounds per square inch at 70" F., or a n absolute pressure exceeding 104 pounds per square inch a t 130' F., or both; or any liquid flammable material having a Reid vapor pressure exceeding 40 pounds per square inch absolute at 100" F." Containers and Shipping On this special pallet, the hinged toe-plate attached to the front secures the cylinders and can be used as a ramp for unloading
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The ICC promulgates regulations which govern shipment of compressed gases by rail or highway in interstate VOL. 49, NO. 10
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commerce. These regulatims require that such gases be shipped in containers manufactured according to ICC specifications and maintained according to prescribed requirements. Most containers must be periodically requalified for continued service. This may be done by hydrostatic testing or, for noncorrosive gases, visual inspection of the exterior. I t is the owner’s responsibility to ensure that these tests or inspections are made and that the date (month and year) of the test is stamped on the cylinder. Furthermore, it is illegal to remove or change these prescribed marks without authority from AAR’s Bureau of Explosives, New York. Cvlinders must not be filled except by or with the consent of the owner and then only in accordance with ICC regulations. These containers are safe for the purposes intended. They are rugged and can be used for many years provided they are not abused. Compressed gases may be stored in stationary containers or ICC cylinders which are manifolded together and charged at the storage site. Such cylinders must be periodically removed for testing and maintenance in accordance with ICC regulations. Stationarv containers should comply with the U n fired Pressure Vessel Code sponsored by either the American Society of Mechanical Engineers alone or jointly with the American Petroleum Institute. or the corresponding code of the governmental authority under which the containers are installed. Piping systems should generally comply with the American Standards Association’s requirements for pressure piping (ASA B31.1). However, piping systems for welding and cutting, therapy oxvgen, and liquefied petroleum gases should comply with the National Fire Protection Association’s standards. The compressed gas industry believes that name of gas legibly applied to the outside of the container is the onlv positive method of identifying its contents. Requirements for marking containers are detailed in American Standards’ 2 4 8 1. “Method of Marking Portable Compressed Gas Containers to Identify the Material Contained.” This is available from the Compressed Gas Association, 11 West 42 St , New York, N. Y . Failure to identify properly the contents of a cylinder can lead to serious injury or fatality. As each cylinder is unloaded from the supplier’s truck, legibility of its label should be checked by the receivinq department. Employees ivho use compressed gases should be trained to read labels and report to their supervisor or safety department any unlabeled cylinder which has inadvertently gotten into the plant. Such a cylinder should be tagged and returned to the supplier un-
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used. This is the recommendation of the Compressed Gas Association. Use of color for cllinder identification invariably becomes an issue in safety groups, governmental agencies, and others having a limited interest in the field. Their opinions reflect a limited point of vieiv \then all uses of compressed gases are considered-about 100 gases or mixtures of gases are shipped in the types of cylinders referred to in this report. There are onl) seven primary colors. Thus, using color for identification requires combinations of one to four colors. This introduces additional possibility of error for several reasons. Users have to learn what various color combinations mean. This involves training, the
effectiveness of which would vary nith individual ability. Also, shades of color Pary considerably under different kinds of light such as mercury vapor and fluorescent. Some painted cylinders used in impure industrial atmospheres, have actually changed color because of chemicals in the atmosphere. Furthcrmore, degree of color preception varies with the individual. In fact, Some people are totally color blind. Ilsing color on cylinders certainly has its place and is essential to good housekeeping, especially \tithin a company, But it should be used only for segregation and ownership identification. Therefore, the need always to identify the contents of a cylinder by the name of the
This special chute built into the side of the truck minimizes damage to cylinders wh iIe un lo o d i11g
INDUSTRIAL AND ENGINEERING CHEMISTRY
S A F E T Y IN C H E M I C A L I N D U S T R Y gas on the label should be impressed on all employees.
lntraplant Transportation Users have the problem of safely transporting compressed gas containers from the receiving dock to the point of use. There are several safe practicese.g., valve protection caps where provided, should be hand-tight when the cylinders are moved; cylinders should not be lifted from one verticle positon to another by the cap, nor should they be dropped on hard surfaces. Release of gas a t a pressure of 2200 pounds per square inch through the approximately 1-inch neck opening will undoubtedly cause a cylinder to “rocket” or “jet.” However, this does not mean that high pressure cylinders are potential missiles ready to take off a t any moment. Actually, high pressure valves are designed and installed so that if struck a sufficiently hard blow, the valve will break off, leaving the inlet in the cylinder. The inlet usually contains a small-diameter hole which restricts flow of gas to a point where the cylinder will move but not rocket. Actual acceleration depends on many factors such as pressure, size, weight; small cylinders usually accelerate much faster than large cylinders. For maximum safety, cylinder valves should be protected. Many devices for intraplant transportation of cylinders have been developed and used successfully-p.g., the “unit system” developed by the general chemical division of the Allied Chemical and Dye Corp. where 12 horizontal nonflammable gas cylinders are piled three tiers high in special wood saddles cut to fit the contour of the cylinders. This pile is then secured tightly with steel bands so that it can be moved as a unit by a fork lift truck. The Dow Chemical Co. has attached a chute in the side or rear of some of their motor platform trucks used for the transportation of cylinders. The chute. about 13 inches in diameter, i s installed at a 45 degree angle with the truck platform and may extend 12 to 24 inches below the platform. A mat or similar device is placed on the ground to absorb the impact of the cylinder. A man on the truck rolls the cylinder into the chute while a second man on the ground retards its descent. Some companies use a round or V-shaped chute that extends from the truck platform ’to the ground at about a 45 degree angle. Another safe way of handling COFtainers by fork truck is by means of a special pallet which holds cylinders properly secured in a vertical position. The pallet has a pipe framework about 3 feet high around three sides and between each row of cylinders. A bar
Always identify the contents of a cylinder b y the name of gas on the label
or chain is placed acress the end of each row of cylinders to hold them in place. A hinged toe plate attached to the front of the pallet prevents the bottoms of the cylinders from slipping off, and when lowered, it provides a ramp for easy loading or unloading. The company that makes Dempster Dumpster containers also makes special devices for safely handling compressed gas cylinders.
Storage and Manifolding Most compressed gas cylinders are equipped with various kinds of safety devices but all are designed to relieve pressure should the cylinder be subjected to conditions such as fire which would dangerously increase pressure. Oxygen is charged into cylinders at pressures of approximately 2200 pounds
per square inch at 70” F. The safety device on a n oxygen cylinder consists of a small frangible disk in the valve which will rupture a t a pressure approximately 5070 higher. The cylinder itself will withstand a much greater pressure unless it is heated intensively a t some localized spot before the pressure in the cylinder can build u p to a point where the safety device functions. Oxygen itself does not burn. However, it does support combustion and when released from a cylinder it may make a more intense fire in the immediate area. As a rule, oxygen cylinders do not add any undue hazard when involved in a general fire. Acetylene cylinders differ from high pressure cylinders in that they are filled with a porous mass saturated with acetone. Acetylene is dissolved in VOL. 49,
NO. 10
OCTOBER 1957
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the acetone under pressure which in a fully charged cylinder is 250 pounds per square inch at 70' F. The cylinder is equiped with fusible metal safety devices which melt a t approximately 212" F. O n large cylinders they are readily distinguishable because they are usually threaded plugs in the tops and frequently in protected places on the bottom of the same cylinders. O n small cylinders, the fusible metal may fill a passage in the valve. When a fuse plug functions and the released gas is ignited, a jet of flame 10 to 15 feet long with accompanying roar, will result. However, the flame will quickly shorten to 3 or 4 feet as pressure in the cylinder is reduced. Most experts agree that burning of gas from a safety device does not signify danger; on the contrary, it shows the cylinder is being relieved of excess pressure which otherwise might cause it to rupture. These same general principles apply to liquefied petroleum gas cylinders. Liquefied petroleum gases are usually contained in larger cylinders containing approximately 100 pounds of gas. Their safety devices usually consist of both a spring-loaded safety relief valve set at 375 pounds per square inch and a small fusible plug. Some cylinders may be protected by either a springloaded valve or fusible plugs. When a spring-loaded relief valve functions, the resulting flame may be 30 to 40 feet long and will remain that length for some time, if the cylinder is subjected to a general fire. Thus, storage of compressed gas cylinders becomes a matter of applying generally accepted fire protection principles. Storage buildings should be of fireresistive construction, well ventilated and well protected from sources of ignition. Cylinders should not be subjected to temperatures above 125' F. and when stored indoors, should not be located adjacent to steam or hot water pipes. When stored out-of-doors in those localities where extremely high temperatures prevail, they should be protected from direct rays of the sun. Flammable compressed gases should be separated or protected from nonflammable compressed gas cylinders. Their flames impinging on the wall of a nonflammable compressed gas cylinder would heat a localized spot intensely before internal pressure could build up to the point where the safety device functions. Poisonous gas cylinders should be separated from other gases and their storage area posted with a suitable sign. Then, in the event of a fire among the nontoxic compressed gas cylinders, firemen would not be subjected to toxic gases or unnecessary hazard. Probably the simplest type of storage building is merely a concrete or paved floor with a roof and four open sides.
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It should have pipe frameworks to section the building, with each section being used for storing a different type of gas. Sections of the flammable and nonflammable gases may be separated by noncombustible partitions 5 feet high. -41~0there should be a fence around the building to preclude entry by unauthorized personnel.
Mechanical and Health Hazard Considerations Some gases are dangerous to life when small amounts are mixed with air. The ICC requires that containers charged with the following materials bear the ICC poison gas label when offered for transportation, and persons handling such gases are advised to contact their supplier for more complete information. Bromoacetone Cyanogen Cyanogen chloride containing less than 0.9y0water Diphosgene E thyldichloroarsine Hydrocyanic acid Lewisite iMethyldichloroarsine Mustard gas Nitrogen peroxide (nitrogen tetroxide) Phenylcarbylamine chloride Phosgene Gases such as carbon monoxide, sulfur dioxide, hydrogen cyanide, chlorine, bromine, and many others produce physiological or pathological responses when inhaled, long before they reduce oxygen concentration to the point of asphyxiation. Gas masks approved for protection against each type of toxic gas should be readily available. Specific first aid instructions for treating exposure to each toxic gas should be prominently posted. Some compressed gases react with certain metals to produce explosive compounds which must be considered when designing piping and equipment. Acetylene, vinyl chloride, vinyl methyl ether, and methylamines react with unalloyed copper to produce acetylides. Acetylene also forms explosive compounds rvith silver and mercury and can react with chlorine and fluorine when subjected to sunlight. Other gases, of course, may react with metals; therefore, either gas suppliers or reliable literature should be consulted for characteristics of gases used. Gases in Laboratories
The safety of laboratory personnel and buildings is important because growth of many companies depend to a large extent on new products and processes developed in the laboratories. But
INDUSTRIAL AND ENGINEERING CHEMISTRY
laboratory work with its temporary setups, high pressures and temperatures, and utilization of many different materials, introduces many potential hazards. Thus, it is doubly important to recognize these hazards and follow applicable safe practices. The fire hazard should be minimized by having in the laboratories only those cylinders being used. Others should be stored outdoors or in special rooms. Cylinders of poisonous gases should be kept and used in fume hoods. Flammable gases should not be used near laboratory burners or similar sources of ignition. Because many different gases and mixtures of gases are used in laboratories, it is extremely important that cylinders be legibly marked with the name of the contents. Cylinders occasionally contain special mixtures of gases; therefore, before connecting for use, contents should always be identified by reading the label. Color of the cylinder should not be relied on. When in storage or use, cylinders should not be subjected to temperatures above 125" F. and must always be secured to prevent falling over. Contents of a cylinder should always be withdraivn through a pressure reducing valve approved for the gas being used. A hose should never be connected directly to a cylinder even for purging. Flammable gases and sqme other gases are oil pumped and may deposit oil films or other organic materials in the reducing valve and hose. Because oxygen may react violently with oil if ignited, regulators, gages, and equipment used with other gases should never be used on oxygen cylinders. When withdrawing liquid from a cylinder, a trap should be provided to prevent baclcflow of liquid into the cylinder. I n addition to these, all other applicable safe practices for storage, handling, and use of compressed gases should be followed in laboratories.
Conclusion Handling compressed gases is not haiardous if logical practices are followed, contents are identified by the label, and cylinders are not abused. Before an accident can be prevented, it must be anticipated. To do this, a thorough knowledge is needed for all properties of the material handled. Therefore, data sheets, and literature available from industry, salety, and insurance organizations should be reviewed. RECEIVED for review .April 7, 19.57 ACCEPTED JUIY24, 1957 Division of Industrial and Engineering Chemistry, Symposium on Safety in the Chemical Industry, 13lst Meeting, ACS, Miami, Fla , April 1957.
