1 It is believed that compliance with the requirements prescribed in these Regulations will provide a high degree of safety in the unloading of tank cars of chlorine. Effective implementation of these requirements is most likely to be realized if the persons involved in the unloading operations have a good knowledge and understanding of the properties and hazards of chlorine.
2 The principal properties and hazards of chlorine are as follows:
(a) chlorine is normally transported under pressure in liquid form in tank cars and cylinders. Under atmospheric conditions, such as would be obtained in the event of a leak, liquid chlorine is rapidly converted to a gas in the ratio of approximately one volume of liquid to 460 volumes of gas. For this reason a relatively small leak of liquid chlorine is capable of polluting a large volume of air;
(b) chlorine gas is about 2 1/2 times as heavy as air. It therefore tends to accumulate in low places and is not readily diluted or dispersed unless it is subjected to strong air currents;
(c) chlorine is not flammable, but at ordinary temperatures it will support the combustion of some combustible, organic substances such as finely divided cork. At elevated temperatures it will support the combustion of steel and for this reason may cause the rapid deterioration of steel piping or other steel equipment that is exposed to a fire;
(d) although insulated chlorine tank cars of the ICC 105A type provide good thermal protection for the lading, they should be removed from the scene of a fire as soon as possible;
(e) dry chlorine is compatible with a wide variety of metals including mild steel, but chlorine containing more than about 150 parts per million of water is highly corrosive to mild steel and other metals with poor resistance to dilute hydrochloric acid. It is, therefore, essential that all piping and equipment be thoroughly dried before it is placed in service and that water be prevented from entering the system by other means; chlorine leaks should not be sprayed with water;
(f) the maximum concentration of chlorine in air that most adult persons can breathe for one hour without serious effects is four parts per million; this is about the minimum concentration that is detectable by odour;
(g) chlorine in concentrations of about 35 parts per million is considered dangerous if breathed for periods longer than about 30 minutes, but because concentrations of chlorine above 15 parts per million are extremely irritating to the throat and respiratory tract it is unlikely that any one would intentionally expose himself for more than a few minutes to such concentrations;
(h) even a few breaths of air which contain more than 1,000 parts per million of chlorine are likely to be fatal;
(i) respirators of the absorbing canister type are not suitable for use in atmospheres containing more than about one per cent of chlorine by volume; self-contained breathing apparatus must be used in such atmospheres;
(j) in addition to the respirators referred to in paragraph (i), persons repairing leaks, or who otherwise may be exposed to liquid chlorine or high concentrations of gaseous chlorine, should wear gloves and other suitable protective clothing; the action of chlorine on the skin and other body tissues is similar to that of acids and other corrosive substances; and
(k) for additional information on this subject the reader is referred to The Chlorine Institute Inc., 342 Madison Avenue, New York City, New York 10017 or to the nearest chlorine producer.
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