in the Chemical laboratory Edited by N O R M A N V . STEERE, School of Public Health, University o f Minnesota, Minneapolis, Minn. 55455
XXI.
Compressed Gas Cylinders and Cylinder
Regulators Used in Laboratories* GEORGE PINNEY, Notion01 Cylinder Gos Division of Chemetron Corp.,
Usage of compressed gases in educational, medical, and industrial lahoratories presents many problems not encountered in industrial use. The prohlems include the wide variety of flammable, toxic, and radioactive materials and their mixtures with properties that are frequently unfamiliar to the researcher, and the propensity of laboratory personnel to modify, adapt, and repair cylinders, valves, and regulators themselves rather than to leave such work to their suppliers or specially trained personnel. Incorporating a cylinder into an experimentd apparatus so that foreign materials can enter the cylinder or the cylinder may he subjected to extreme pressures is an extremely hazardous practice that is unfortunately fairly common. What is a compressed gas? The regulations of the Interstate Commerce Commission state that a compressed gas is one having a pressure in the container of 40 psia or greater at 70'F ( 2 1 T ) or, regardless of the pressure st 7 0 T , having an absolute pressure exceeding 104 psi a t 130°F (54°C). I n addition, a?y liquid flammable material having a R e ~ d vapor pressure exceeding 40 psia at 100°F (38-C) is clasdied a compressed gas. The regulations define the minimum pressure in a cylinder, hut the maximum pressure can range from a low of a few pounds for poisonous or radioactive materials to 6000 psi or above for the non-condensihle gases. The maximum working pressure for the common 3A and 3AA seamless steel cylinders is stamped permanently into the metal of the cylinder near the valve. This pressure may he exceeded by 10% if certain additional requirements are met. Regardless of the pressure rating of the cylinder, the pressure of the gas in the cylinder will depend to a great extent on its physical Etate. So-called permanent gases have a, pressure more or less in direct proportion to the remaining contents. Gases which are liquefied in the cylinder, such as carbon dioxide, propane, am-
* Fmm the Proceedings of the Twelfth National Conference an Campus Safety, June, 1965, Central Michigan University; available at $1.80 from the Higher Education Section, National Safety Council, 425 North Michigan Avenue, Chicago, Illinois 60611
monia, etc., will exert their own vapor pressure as long as any liquid remains or their critical temperatures are not exceeded. The cylinder sises encountered are equally varied, ranging from the common lecture bottle 2 in. X 15 in. and weighing about 3 lh, through the large industrial type, 9 in. X 55 in. and weighinggp to 140 lb. Compressed gas cylinders a n be used in laboratories with complete safety if the following general rules are complied with completely during cylinder receiving operations, storage, transportation to the laboratory or other use point, usage, and empty cylinder disposal. Know Contents of Cylinder
No cylinder should he allowed to enter or remain on your premises unless its contents can he quickly and completely determined by the wording on the cylinder or on a tag securely attached to the cylinder. If the tag becomes detached or the label is defaced, the cylinder should not be used but should he marked "unidentified" and placed in the empty stock for return to the supplier. Do not remove this identilieation from empty cyliiders as this might present a hazard to your supplier. Do not rely m a wlor code as this will vary from supplier to supplier. An example of this is that one company paints hydrogen cylinders red while another supplier paints his oxygen cylinders red. Also, colon appear different under artificial light; and, finally, msny persons are color blind. Know Properties of Contents
Knowledge of the properties of cylinder contents is primary to a laboratory operation due to the unusual uses to which gases may be put, as well as the uncammon gases or gas mixtures used. Not only should the flammability, corrosiveness, or oxidation potential he known hut the physiological properties must he kept in m i n d s u c h as toxic, anesthetic, or irritating qualities. Two examples are that toxicity and flammability of carbon monoxide must both be kept in mind, while for hydrogen sulfide its toxicity and ability to desensitize the sense of smell should h~ recognized.
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G. G. Pimey is a Senior Engineer with the Nationill Cylinder Gas Division of Chemetron Corporation, where he has been employed since 1949, and has responsibilities for oxygen production, quality control and high pressure containers. G. G. Pinney graduated from the University of Wisconsin in 1948 with the degree of Bachelor of Science in Chemical Engineering and holds membership in the American Chemioal Society, American Institute of Chemical Engineers and the Instrument Society of America. Mr. Pinney represents his company on Compressed Gas Association technical committees on Cylinder Specification, Cylinder Testing, Safety Devices, and Valve Standards. He has been chairman of the Valve Standard~Committee and is currently sewing as vice-chairman of the Safety Device Committee and chairman of the General Technical Committee. L Hondle Cylinders Carefully
Cylinders are primarily shipping cantainers and as such are constructed to he as light as possible consistent with safety and durability. Rough handling or abuse, such as usine a cvlinder for a roller t,o
Store Cylinders Appropriofely
Store and use in ventilated areas away from heat or ignition sources. Store flammables zwrty from other gases. Limit the quantity stored in one location. Cylinders containing gases under high pressure could very quickly render an area. unsafe if the large volume of gas should he released. Most cylinders, except those containing toxic or radioactive gases, are equipped with safety devices of one form or another. The devices may function prematurely if cylinders are heated to a temperature in excess of 1 2 5 T (5Z°C). Also cylinders containing low vappor pressure liquids could become liquid-full s t elevated pressures and burst. If a cylinder must he heated, this should be done in a very well thermostated water bath heated to not more than 125°F. In oneindustriallaboratory a researcher, in an effort to increase the flow rate of propane from a. cylinder, turned an infrared heat lamp on it from a distance of about four inches. This lamp was aimed at a fusible metal plug which shortly released and jetted a stream of liquid propane on the heat lamp. For some reason the gas did not ignite even though the researcher had left the room. If the gas had ignited the resultant explosion and fire could have leveled the entire hhoratory.
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Fosten Cylinders Securely In Use O r Sforoge
If a cylinder should fall or roll off a bench it might break off the regulator, releasing a large quantit,y of gas and causing the cylinder to pin-wheel, which can break a person's legs; another danger is that the valve could shear off and the cylinder might "rocket" like a projectile doe to release of pressure. Tronsport Cylinders Sofely
Transport large cylinders only on a wheeled cart. Do not slide or roll them, since it is easy to lase control of a cylinder while rolling or dragging i t no matter how much practice a man might have. If one falls it could land on the foot, severely crushing the toe bones. When a cylinder is dragged, the valve protective cap may pull off and strike the man in the face. Mishandling of cylinders in transit is the cause of many pulled muscles and back injuries. Do Not Tomper with Cylinders
Never tamper with any part of a valve such as the safety nut or stem packing nut. A typical large cylinder valve is shown in Figure 1 with the safety nut shown on the left and the packing nut just below the handle. A leak at either place ia potent,ially hazardous; such cylinders should he marked as leakers and removed to an open area until picked up by the supplier. Do not put unmarked leaking cylinders in the empty pile, as it is eontra'y to Interstate Commerce Commission Regulations to ship leaking containers by common carrier. There have been fatalities in laboratories caused by unfamiliarity with valves. I n one instance, the safety nut was confused with an outlet cap, which is frequently installed on the outlet, and the safety nut was completely removed. Unfortunately, the gas was carbon monoxide. You will note that the safety nut eonneots directly to the valve inlet and onee removed, the flow of gas cannot he stopped. Do Not Strike Arcs on Cylinders
Do not strike snelectricarc on cylinders. This rule is applied ~rimarilyto industrial use, where inert Kases are used for shielded arc welding. It is very tempting to test the arc on the large metal surface. Arc burns, however, not only are stress raisers, but, due to metallurgical changes, codd cause the heat-affected portion of the cylinder to become brittle. Use Compressed Gores with Appropriote Equipment
Use cylinders only with equipment suitable for the contents and do not farce the connection or use homemade adaptors. The importance of this rule cannot be overemphasized. Accidents have occurred because of attaching flammable gas regulators to oxygen cylinders, improperly identifying the contents of a cylinder, and
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eome lower than the pressure in some other part of tho appnratus. Close Volves on Empty Cylinders and M a r k The Cylinder "Empty" If cylinders are returned to the supplier with the v s l w open, t,he interior will Reeome contnminated with atmospheric air and moistnl.e. Surh cylinders cannot be used for high pority gases without an extensive reronditionirtg. If the cylinder had contained such materials as anhydrous hydrogen chloride, chlorine, et,c., this resultant humid atmosphere would corrode the cylinder ver,v rapidly. Empty cylinders should be so marked and stored s e p smtely to avoid returning full cylinders to the supplier or sending empties to a laboratory or other use point. Never Attempt To Refill o Cylinder I t is very tempting to refill your own small rylinders from large ones by interconnecting them with high pressure t,ubing. There are n number of reasons why this practice is hazardous. The cylinder being filled may, unknown to you, have a lower working presswe than the large cylinder. Too rapid a filling can result in extremely high cylinder temperatures ~ v l ~ i r rould h damage the valve. The cylinder being filled may contain a residue of some reartive materid. For cylinders rontaining liquids, the ICC prescribes filling weight,^ which result in n vappor space in the cylinder a t temperatures and presalres up to that s t which the safety device fnnct,ions. If these weights are exceeded, t,he cylinders may become liquid-fdl s t room lemperstures and fail. At e x h refilling ,your srtpplier gives all rylindprs a cnrefnl visual inspertian for defects, some of which are no1 obvious, and gives those cylinders which require it n hydrostatic pressure test every five years. Allother cylindea must he given extremely t,horo~~glr internal and external v i s d inspertim at stated intervals. This inspectiun nud testing can be best performed by one having a thorough knowledge of cylinders. Finally, at least one supplier of laboratory gases uses a very lightweight minimum-design cylinder which is classified as non-refillable by the ICC. I n ot,her words, f u r safety reasons such a cylinder must be discarded after use the same a? the common sernsol spray cans. Further Informotion Much valuable information on the nthjeet of cylinders and safety is contained in t,he various pamphlets of the Compressed Gas Aasoriat,ion, the Chlorine Inst,itute, the hlnnufacturing Chemists Association, the Iiational Safety Council, ete. Pamphlets available from the Compressed Gas Association inelnde those on Acetylene, Ammonia, Sulphur Dioxide, Oxygen, Hydrogen, and Carbon Dioxide. The pamphl~tsare separated into groups on
