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Chlorine at Treatment Plants

Chlorine at Treatment Plants

Posted by Dr. David J. Silver, B.S., M.S. Ph.D., CIH on Apr 12th 2019

Chlorine gas exposure can occur at water treatment plants, paper plants, and large public pools. Chlorine has a very pungent odor and if released into the air, people may be exposed through skin contact or eye contact. They also may be exposed by breathing air that contains chlorine. Where there is a possibility of overexposure, a monitoring system can be used effectively for leaks and possible overexposures. Fixed stationary monitors are typically placed in high risk areas, whereas, workers may continuously wear a personal chlorine monitor. Alarms for OSHA permissible exposure limits or action levels can be preset according to the desired airborne concentration.

Chlorine Toxicity

Chlorine gas is greenish yellow in color and is heavier than air. It’s an excellent disinfectant; however, it is an occupational hazard to workers at treatment plants and other industries. Chlorine gas is highly irritating to mucous membranes including the lungs, eyes, ears, nose, and throat. Chlorine odor is detectable at 0.1 to 0.3 ppm in air and can be tolerated for an hour. At 5 to15 ppm, there is moderate irritation. Above 30 ppm, there is immediate sub sternal chest pain, shortness of breath, and coughing. At approximately 40–60 ppm, a toxic pneumonitis and/or acute pulmonary edema can develop. Concentrations of about 400 ppm and beyond are generally fatal over 30 minutes, and at 1,000 ppm and above, fatality ensues within a few minutes. The OSHA permissible exposure limit is 0.5 ppm (8hrTWA) with a 15 minute short term exposure limit of 1 ppm.

Chlorine Uses

Industrial uses of chlorine gas are water treatment plants and paper production. Chlorination is by far the most common method of wastewater disinfection and is used worldwide for the disinfection of pathogens before discharge into receiving streams, rivers or oceans.(11-14) [J1]. Chlorine is known to be effective in destroying a variety of bacteria, viruses and protozoa, including Salmonella, Shigella and Vibrio cholera.

At Risk Personnel

Exposure may occur through breathing, skin and eye contact if an accident involving chlorine takes place nearby, such as a liquid chlorine spill, a leak from a chlorine tank, or a leak from a facility that produces or uses chlorine. Exposure may occur if household chemicals are mixed like toilet cleaner and bleach. Mixing household cleaners containing ammonia with bleach may also release dangerous chemicals into the air. The improper use of swimming pool chemicals can cause chlorine exposures. Wastewater treatment and paper manufacturing processes may expose workers to higher releases of chlorine than others. People who work in places where chlorine is made or used may be exposed to low levels over a period of time. Exposure to chlorine gas also may occur in the vicinity of an accidental spill or industrial mishap such as a chlorine tank spill or rupture. Workers at facilities that produce, transport, or use chlorine may be exposed to low concentrations of the gas. Workers may also be exposed to high chlorine concentrations if an accidental release occurs at a facility.


Chlorine gas can present a significant threat to health and safety in work environments. Thus, identification and quantification through air monitoring is an essential component of a health and safety program. The steps for this include:

a) selecting personal protective equipment,

b) delineating areas where protection is needed

c) assessing the potential health effects of exposure, and

d) determining the need for specific medical monitoring.

Direct reading chlorine gas monitors with alarms are able to provide warnings and instant levels, and the data logging models can also provide 8 hour time weighted averages. Measurement values can alarm and be compared to peak exposures and time weighted exposures.

The MPower Single Gas Chlorine Detector

The MPower UNI MP100 offers a simple portable solution for the widest array of toxic gas and oxygen (O2) applications on the market. In addition to typical sensors such as carbon monoxide (CO), hydrogen sulfide (H2S), nitrogen (NOx), ammonia (NH3) and sulfur dioxide (SO2), we also offer less-common sensors including hydrogen fluoride, phosphine, ozone, ethylene oxide, methyl mercaptan, and acetaldehyde. Chlorine gas is offered at 10.0 ppm with 0.1 ppm resolution. The monitors have a large LCD providing maximum readability in the field and are made with six bright red LEDs allowing for a quick alarm notification. Constructed of strong and durable material, the UNI is designed to be comfortable yet drop-resistant. The UNI series can easily be bump tested and calibrated with the mPower CaliCase System.

EGas Depot Chlorine Calibration Gas

To maintain your chlorine gas monitor and to assure that it is reading correctly, your gas monitor should be calibrated daily or when you want to be assured its reading correctly. Chlorine gas for calibrating your mPower gas detector is available at EGas Depot. Order online at or call toll free at 833-264-0730.