Professional Engineeing Publication

1) Introduction

With the greatly increased use of chlorine and chlorine compounds, there appears to be at the same time less and less understanding and concern about safe handling, storage and use. Great respect, and oftentimes fear, is still the general attitude in regards to chlorine gas. Calcium hypochlorite and sodium hypochlorite are treated quite lightly in regards to care and safety when, in fact, they have moved far ahead of chlorine gas in the direct or indirect cause of death, injury and property damage.

A good example of the lack of understanding is the fact that so many health and engineering organizations insist upon chlorine gas cylinders and equipment being located in a separate, well-ventilated room-while hypochlorination supplies and equipment are allowed to be placed in any convenient location. For greatest safety, all chlorine and chlorine compounds should be placed in separate, well-ventilated rooms, as well as the feeding equipment, and in the case of hypochlorite, even extra precaution should be taken.

2) General

Chlorine is an element and, when supplied in its basic form, is a liquefied gas under pressure. Chlorine in pressurized containers is in the form of both liquid and gas. The element chlorine is oftentimes combined with other compounds to make it easier to package and handle, and to be able to use other types of feeding equipment than required with gas chlorine. The most common powder form (and tablet form) is calcium hypochlorite, while the liquid preparation is sodium hypochlorite which is available in various strengths and is known as bleach or laundry bleach.

Chlorine gas, itself, is primarily a respiratory irritant and depending upon the concentration in the atmosphere, as well as the duration of the exposure, it can be only mildly irritating or, in extreme cases, can even cause death. Chlorine gas is not just obtained from a gas cylinder, but is also given off from calcium hypochlorite and sodium hypochlorite. This means that regardless of the form in which chlorine is obtained, the fumes themselves are equally as dangerous.

The United States Bureau of Mines indicated that most people cannot detect chlorine in the atmosphere at a concentration of less than about 3.5 pounds of chlorine per million pounds of air (PPM). However, they further state that at only 5 PPM the mixture is noxious and impossible to breathe for more than several minutes. At slightly higher values that this, you run into irritation, coughing and truly hazardous conditions. You can readily see from these values that anytime you can smell chlorine, you are in a hazardous atmosphere and should not remain.

Chlorine gas, itself, is neither explosive nor flammable. It is, however, a very strong oxidizing agent and will react with almost all elements and with many inorganic or organic compounds. In doing so, the reaction usually gives off heat. With chlorine gas obtained from cylinders, there is very little fire hazard. On the other hand, calcium and sodium hypochlorite appear to be non-hazardous, but often react violently when in contact with many ordinary materials - and/or with heat, spark or flame present.

Moist chlorine is very highly corrosive as a result of the formation of hydrochloric and hypochlorous acids, and neither equipment nor supplies - in any form - should be located so that chlorine will come in contact with electrical equipment or other equipment that will be damaged by corrosion.

3) Liquid Chlorine (Chlorine Gas)

Pure chlorine is shipped in steel containers in which the chlorine is both in the liquid and gas phase. Since the chlorine has been thoroughly cleaned and dried before being placed in the containers, it is non-corrosive to the steel. The chlorine cylinder valves are of a very heavy construction and are additionally protected during handling by a heavy steel hood. Since chlorine in the cylinders is under pressure, and the pressure increases with temperature, the cylinders are further protected from bursting by a fusible plug which is designed to melt at between 158^oF and 165^oF. In the case of fire, this plug would melt allowing the chlorine gas to escape, rather than allowing pressure to build up, which might eventually rupture the cylinder and cause pieces of metal to be thrown out. Here, basically, are the more common safety rules for handling and storage:

1. When moving cylinders, the valve protection hood should be in place at all times.
2. Cylinders must not be dropped or struck with any force.
3. A safety chain or strap should be placed around the cylinder and affixed to a wall, pipe, etc. to prevent tipping over in the event the cylinder is accidentally hit or pushed.
4. Cylinders should be stored in an upright position.
5. Cylinders should not be stored near a ventilating system, passageways, or below ground in unventilated rooms.
6. Grease or oil should never be on, or around, chlorine fittings or connections.
7. If there is any indication of the presence of chlorine in the air, immediate action should be taken to correct the condition. Chlorine leaks that are left alone will always get worse.
8. If an extensive chlorine leak is found, all persons should be kept away from the area - preferably up - wind and at a higher level.

4) Calcium Hypochlorite

Calcium Hypochlorite is most usually supplied as a powder or in small granular form, although in some cases it is compressed into tablets. In these forms, it can more easily be packaged in small quantities, can more easily be transported, and is relatively simple to handle if very careful precautions are taken. Contrary to popular belief, this "safe" form of chlorine causes a great number of accidents of all types. The innocence of appearance and packaging can be very misleading. Although chlorine is purchased in this form 'supposedly' for ease of handling and safety, the opposite is often true and the cost of the compound itself is at least three or four times as much per pound of chlorine as compared to chlorine purchased in the pure form.

Some health agencies, engineers, and many users often feel that this form of chlorine supply is safe and simple to handle, but in truth it is far more hazardous than chlorine gas due to lack of understanding and suitable precautions. Examine closely the care and handling rules which are summarized from the basic information put out by the manufacturers:

1. Never mix calcium hypochlorite with anything but water.
2. Store in a cool, clean dry area in the original container and always keep covered. (most safe containers have a plastic bag liner which should not be removed and which should also be carefully closed and sealed.)
3. The storage area should be clean and removed from any combustible material and should not be located where chlorine fumes will cause corrosion to equipment.
4. Metal drums should be kept upright and should not be dropped, rolled or skidded.
5. When measuring calcium hypochlorite, you should use only a plastic, glass or enameled measuring device that is completely clean, dry and free of all foreign matter.
6. Calcium hypochlorite, as a strong oxidizing agent, must not be brought into contact with heat, acids or any combustible materials. These materials include paper, rags, beverages, tobacco, oil base products, etc. Matches, fire, lighted, cigarettes and any form of heat must be kept away.
7. Whenever handling calcium hypochlorite, the hands must be clean and dry and gloves should never be worn. Hands should be washed after handling.
8. Never permit calcium hypochlorite to contact the eyes. Any spilled calcium hypochlorite should immediately be flushed thoroughly with water.
9. Always rinse empty containers thoroughly with water.

Small oversight in adhering strictly to the rules of safe handling of calcium chlorite can prove disastrous. There have been several occurrences where a new, sealed container dropped while unloading has caused explosion and fire which destroyed property and put many people, severely burned, in the hospital. Almost instantaneous explosion has occurred due to oily rags, banana peels, etc. being thrown into, a partially filled container can be quite violent. An oily rag, wad of paper or other combustible can be equally as serious. Motels have burned down, storehouses completely destroyed, and many people seriously injured from careless handling and storage of this material. Unfortunately, many accidents have occurred for unexplained reasons while operators were simply dipping a supply from the container or carrying a supply in the same manner that they had hundreds of times before - but suddenly there was a violent explosion.

5) Sodium Hypochlorite

Sodium hypochlorite is a liquid supplied in various strengths of available chlorine. Again, we are interested only in the amount of chlorine required and in ease of handling. Common household laundry bleach is 5.25% available chlorine by weight. Solutions of approximately two and three times this concentration are available. In this form, the chlorine solution is generally supplied in glass or plastic containers and is relatively easy to handle, although the cost as compared to pure chlorine is three to ten times as much depending upon the source and the concentration.

Since sodium hypochlorite is a liquid, the hazards of fire and chlorine fumes are often underestimated and the same basic rules of safety as given above for calcium hypochlorite should be followed. Many accidents and deaths have occurred with even the relatively weak household bleach, but individual instances are not highly publicized and the hazard often over-looked. Here are some of the basic rules in addition to those listed above:

1. Store in a cool, dark area away from possible falling objects or physical damage.
2. Avoid contact of sodium hypochlorite with the eyes or with the skin.
3. Keep container tightly closed and keep away from combustible materials.
4. If spilled, wash down thoroughly and do not allow to remain in contact with cloth, paper, oil products or other combustible matter.
5. Keep containers away from heat and fire.
6. Never use in conjunction with acids, vinegar, toilet bowl cleaners or any other cleaning agents.

The use of sodium hypochlorite as a bleaching and cleaning agent - such as in the home - has caused several deaths when used along with other agents which released chlorine fumes. Fires have occurred where rags and other combustible materials soaked with sodium hypochlorite have been allowed to stand and/or where a heat source may have been present.

6) Conclusion

Chlorine as a gas has been feared and/or treated with respect primarily due to its use during World War I as a poison gas. No one doubts its toxicity or its potential hazard and, therefore it is usually treated with respect. Most people do not know the true facts about chlorine and its compounds and therefore grossly overestimate the hazards of liquid chlorine (chlorine gas) and oversimplify the hazards connected with its compounds such as calcium and sodium hypochlorite.

Government reports on the many tens of thousands of gas cases during World War I are remembered, but it is overlooked that only about two thousand cases were from chlorine gas and that only seven deaths occurred. Since chlorine remains as an everyday word, it is forgotten that mustard gas, phosgene and other gases were actually the problem. In addition, newspaper, magazine and other reporting media tend toward sensationalism which makes accidents involving a large number of people nationally important. Individual accidents have only local importance. In several years there have been chlorine gas leaks in public locations where dozens or more than a hundred people have been involved, and this received national publicity. Follow-up of these incidents was not as publicized and where chlorine gas was involved you find very little news - since recoveries were complete, quick and injuries comparatively negligible.

Large fires, serious burning and extensive damage caused by calcium or sodium hypochlorite are usually reported locally and do not receive much more publicity than a local car accident... they do not involve a large number of people. Unfortunately, the reporting still refers to chlorine or chemicals rather than specifically to the form of compound that was involved.

Local reports told the following: "A large fire completely destroyed a motel in southern California- "three men were very seriously burned when unloading powdered chlorine in Toledo" - "a swimming pool distributor's warehouse was destroyed by fire in Texas" - "a bath house and filter room in St. Louis were destroyed by fire with injury to several when powdered chlorine ignited" - "two deaths in Illinois of housewives attributed to household bleach used in conjunction with other cleaning fluids". These are only a few of the many accident cases that occur every year when using calcium or sodium hypochlorite with disregard for their hazard.

Statistically and actually, chlorine gas is the least hazardous and safest form of chlorine available today, while at the same time being the most economical. Antiquated regulations and general dissatisfaction with chlorine gas were based primarily upon very high-priced equipment, extremely expensive maintenance and complication of operation. Modern technology and improved materials have eliminated these drawbacks, but lack of education in regards to safety and modern equipment has condoned practices that are well behind the times.