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Chlorine Safety for Water Treatment Operators

Chlorine is an effective and economical antibacterial used to destroy and deactivate a wide range of bacteria and viruses in homes, hospitals, swimming pools, hotels, restaurants and other public places. Chlorine used in pool operations is supplied in three forms: 

  • Sodium hypochlorite—a liquid when in dilute form is commonly known as bleach 
  • Calcium hypochlorite—a powder or tablet 
  • Chlorine gas—supplied in 150-lb. cylinders 

Due to the inherent hazards of chlorine-containing materials, swimming pool operators should be trained in the safe use, handling and storage of these chemicals. Training should include a discussion of the hazards, emergency response procedures, first aid and pool chemical safety rules. 

Chlorine is an effective and economical germ killer that is used to destroy and deactivate a wide range of dangerous germs in homes, hospitals, swimming pools, hotels, restaurants and other public places. Chlorine is supplied in three basic forms: 

  • Sodium hypochlorite—a liquid when in dilute form is commonly known as bleach 
  • Calcium hypochlorite—a powder or tablet 
  • Chlorine gas—container sizes range from 100 lb. cylinders to rail cars 

Due to its inherent hazards of chlorine-containing materials water treatment operators should be trained in the safe use, handling and storage of these chemicals. Training should include a discussion of the hazards, emergency response procedures, first aid, personal protective equipment (PPE) and safeguards that prevent chlorine overexposure. 

Why is Drinking Water Treated with Chlorine?

Before cities began routinely treating drinking water with chlorine, thousands of United States residents died each year due to cholera, typhoid fever, hepatitis A and dysentery. Drinking water chlorination and filtration helped virtually eliminate these diseases in the United States and other countries. 

During the treatment process, chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite solution or dry calcium hypochlorite. Almost all systems in the United States that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. 

Potential Dangers to Bulk Chlorine Users 

Chlorine presents several hazards to users. Elemental chlorine (chlorine gas) is corrosive when it contacts moist tissues such as the eyes, skin, and upper respiratory tract. At low levels it is an irritant, while higher levels could lead to permanent injury or death. 

Contact with liquid chlorine can result in chemicals burns or frostbite. And while chlorine is not flammable or combustible, it is an oxidizer. This means it will support combustion and can react explosively if in contact with organic materials such as oil, grease, wood and rags. 

Bulk Chemical Handling for Chlorine

People can be seriously injured when chlorine is improperly mixed with other chemicals, especially acids or acidic materials. In a water treatment plant, this mixing usually occurs by accident. For example, when a tank truck of acidic chemicals is unloaded into the sodium hypochlorite solution (bleach) storage tank. 

Some common acidic chemicals found at water and wastewater plants include ferric chloride, ferric sulfate, ferrous sulfate, ferrous chloride (pickle liquor), aluminum sulfate (alum), aluminum chloride, hydrochloric acid, sulfuric acid and phosphoric acid. Under the right circumstances, these chemicals can react with sodium hypochlorite to release hazardous chlorine gas. 

How to Prevent Chlorine-related Accidents in Waste Water Treatment Plants

Several steps can be taken to prevent chlorine-related accidents.

Extensive training—Government regulations require that only specified operators highly trained in the unloading process should be assigned the duty of accepting tank truck or tank car deliveries. 

Secured tank loading lines—Prevent truckers from unloading without supervision by installing blind flanges or caps equipped with a padlock.

Visually define lines—Use color coding and labeling to differentiate different process lines and fittings. You can also change the fittings on the loading lines to different sizes or types for each line. 

Checklist—Create a checklist that your authorized operator must complete before accepting a chemical delivery: 

  • Confirm the name of the chemical and the concentration 
  • Review the shipping papers and the placards of the truck or tank car
  • Confirm proper PPE is used and emergency equipment is available 
  • Confirm the volume being delivered does not exceed storage capacity 

You can help truck drivers avoid mistakes by placing signs on sodium hypochlorite unloading lines. Keep signs brief and to the point. Signs should be large enough to be visible from at least 10 feet away. Storage sites should also consider placing stickers with the same wording on the actual sodium hypochlorite piping.

Safety Devices and Information for Packaged Chlorine Users 

Emergency valve closure systems—Equip systems with valves and/or actuators that close automatically, stopping the flow of chlorine. These units should only be used to close valves in an emergency, not as a routine part of your operation. 

Line pressure warning system—Chlorine release can occur when a container is disconnected while the line is still under pressure and/or the container valve did not close properly. Consider installing a pressure sensing device in the line to ensure the chlorine line is depressurized before disconnecting.

Direct mounted vacuum chlorinators—These devices attach directly to the cylinder or vapor (upper) valve on a container. They require a vacuum in the system to operate. If the vacuum is lost due to either a break in the system or the loss of water flow through the venturi injector, then the vacuum chlorinator will stop the flow of gas.

Atmospheric monitoring equipment for chlorine—This equipment can be used to detect leaks and monitor chlorine levels. Fixed area detectors are not intended to monitor personnel exposure or to quantify leaks in the absence of other input. Many states and local municipalities have established rules that require the use of these monitors for specific situations.

Acid detecting paint—This paint changes color from yellow to bright red when it is exposed to acidic gases like chlorine. The paint returns to its normal color after the leak is stopped and the leak site is neutralized.

Chlorine and Water System Security 

The Department of Homeland Security has issued Chemical Facility Anti-Terrorism Standards (CFATS) for any facility that manufactures, uses, stores or distributes certain chemicals at or above a specified quantity—this includes chlorine. 

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