Elemental chlorine is a highly reactive, greenish yellow gas. It has a suffocating, irritating, pungent bleach like odour that is detectable at low concentrations (above 0.3 – 0.5 ppm). Continuous or high-level exposure of the Cl2 can quickly deaden a person’s sense of smell, making the odour of Cl2 an unreliable indicator of its presence. Hence, other means such as chlorine monitoring is a viable solution to provide adequate warning of hazardous exposure. This article covers information on chlorine gas, its sources in the ambient air, permissible levels, health and environmental impact, possible corrective measures, need for chlorine monitors as well as different methods of H2S monitoring. What is Chlorine? Molecular structure of Chlorine [Source: https://pubchem.ncbi.nlm.nih.gov/compound/Chlorine] Chlorine is a highly reactive, greenish yellow gas. It has a suffocating, irritating, pungent bleach like odour that is detectable at low concentrations (above 0.3 – 0.5 ppm). Cl2 is heavier than air which causes it to remain in low-lying areas or areas near ground with little air movement. Chlorine gas is slightly soluble in water, Hence, it reacts to form hypochlorous acid (HClO) and hydrochloric acid (HCl). It is not flammable but has an ability to react explosively when combined with other substances such as hydrogen, ammonia, fuel gas, acetylene, ether, etc. Cl2 gas is oxidizing in nature and has bleaching properties. It is toxic to human and plant life and can corrode metals and other materials. Chlorine in the Atmosphere Elemental chlorine is rarely present itself in nature due to its high reactivity. It can be formed from atmospheric reactions of chlorine-containing compounds with NO2 and through oxidation of chlorides in presence of strong oxidants in the atmosphere such as ozone. Once released, it rapidly combines with other chemicals/compounds in the atmosphere to form secondary compounds instead of remaining in pure elemental state. Chlorine dissolves in the water and reacts to form chloride salts and chlorinated organic chemicals such as sodium chloride (NaCl, common salt), sodium hypochlorite (bleach), chloroform, etc. Sources of Chlorine Chlorine gas is commonly used as household cleaner and disinfectant oxidizing agents in water treatment to disinfect drinking water as a disinfectant in industrial applications such as food processing, pulp and paper mill and water cooling systems, etc. in the bleaching process in pulp and paper mills and ink removal from recycled paper in the manufacturing of many products such as paper, antiseptic, insecticides, paints, petroleum products, textiles, medicines, etc.

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Chlorine (Cl2)
All you need to know about...

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All you need to know about Chlorine (Cl2)WHAT IS Cl2?
It is not flammable but has an ability to react
explosively when combined with other substances
such as hydrogen, ammonia, fuel gas, acetylene, ether,
etc.
Chlorine is a highly reactive, greenish yellow gas with a suffocating, pungent
bleach like odour that is detectable at low concentrations (> 0.3-0.5 ppm).
Cl2 is heavier than air which causes it to remain in low-lying areas or areas near
ground with little air movement.
Cl2 gas is slightly soluble in water. It is highly oxidizing
in nature and has bleaching properties.

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All you need to know about Chlorine (Cl2)Cl2 IN ATMOSPHERE
● Elemental chlorine is rarely present itself in nature due to its high reactivity.
● It can be formed from atmospheric reactions of chlorine-containing
compounds with NO2 and through oxidation of chlorides in presence of
strong oxidants in the atmosphere such as ozone.
● Once released, it rapidly combines with other chemicals/compounds in the
atmosphere to form secondary compounds instead of remaining in pure
elemental state

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All you need to know about Chlorine (Cl2)SOURCES
Chlorine gas is commonly used:
● as household cleaner and disinfectant
● oxidizing agents in water treatment to disinfect drinking
water
● as disinfectant in industrial applications such as food
processing, pulp and paper mill and water cooling systems,
etc.
● in bleaching process in pulp and paper mills and ink removal
from recycled paper
● in manufacturing of many products such as paper,
antiseptic, insecticides, paints, petroleum products, textiles,
medicines, etc.

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All you need to know about Chlorine (Cl2)PERMISSIBLE LIMITS
Recommended limits for Cl2 in a workplace
OSHA (PEL) OSHA (PEL) NIOSH
(REL)
NIOSH
(IDHL)
AIHA ERPG-
1
AIHA ERPG-
2
AIHA ERPG-
3
Cl2
levels
0.5 ppm TWA 1 ppm STEL 1 ppm STEL 10 ppm 1 ppm 3 ppm 20 ppm
Permissible Exposure Limit (PEL) given by OSHA (Occupational Safety and Health Administration) defines the
maximum concentration of Cl2 to which an unprotected worker may be exposed to.
PEL may reference an eight-hour time-weighted average (TWA) or a 15-minute short term exposure limit (STEL)
concentration that cannot be exceeded for any period.
Recommended Exposure Limit (REL) and Immediately Dangerous to Life of Health (IDLH) are the occupational
exposure limit recommended by NIOSH (National Institute for Occupational Safety and Health)
Emergency Response Planning Guidelines (ERPGs) are exposure guidelines given by AIHA (American Industrial
Hygiene Association).
[Source: https://www.chlorineinstitute.org/stewardship/chlorine/health-hazards/]

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All you need to know about Chlorine (Cl2)ADVERSE IMPACTS
HEALTH IMPACTS OF Cl2
● Chlorine is majorly toxic due to its oxidizing
and corrosive properties. Cl2 gas reacts with
moisture in the tissues and forms toxic
products such as hydrogen chloride (HCl) and
hypochlorous acid (HOCl) that causes damage
to tissues and cell structure of the body.
Cl2 + H2O ↔ HCl + HOCl
● Symptoms of Cl2 exposure are given here.
[Source: Agency for Toxic Substances and Disease Registry, National Library of
Medicine.]
● Continuous or high-level exposure of the chlorine can quickly deaden a person’s sense of
smell, making odour of Cl2 an unreliable indicator of its presence. Hence, other means such as
the use of Cl2 monitors is a viable solution to provide adequate warnings of hazardous
exposure.

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All you need to know about Chlorine (Cl2)ADVERSE IMPACTS
● Chlorine gas does not have a direct impact
on the environment. However, it contributes
to environmental problems such as ozone
layer depletion, global warming and acid
rain. Cl2 in the atmosphere destroys the
ozone molecules.
● Additionally, chlorine gas rapidly combines
with other compounds to form chemicals
such as dioxins. These dioxins pollue water,
contaminating fish which is then consumed
by larger animals and humans.
ENVIRONMENTAL IMPACTS OF
Cl2

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All you need to know about Chlorine (Cl2)CORRECTIVE
MEASURES
The primary action is Cl2 monitoring i.e. to measure how much of chlorine concentrations
you are exposed to. In addition to this following corrective measures can be taken:
● Avoid going to or staying in low lying areas near the source of Cl2.
● If the presence of Cl2 is detected, immediately vacate the area and provide proper
ventilation to remove the gas.
● Use appropriate respiratory protection or any other personal protective equipment
(PPE) when the exposure is detected.
● Also, avoid spending time in the areas downwind of industries emitting chlorine.

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All you need to know about Chlorine (Cl2)MONITORING METHODS
Non-Dispersive UV Absorption Spectroscopy
(NDUV)
When the gas sample in the chlorine monitor is
exposed to ultraviolet light, the UV radiation at a
particular wavelength is absorbed by the Cl2 molecules
present in the gas sample is measured by the detector
and converted to chlorine concentration.
Semiconductor
When sensor is exposed to air sample, the Cl2
molecules react on the metal oxide surface of the
sensor and dissociate into charged ions which alter the
resistance of the film which is measured and converted
to the Cl2 concentration.

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All you need to know about Chlorine (Cl2)MONITORING METHODS
Electrochemical
Cl2 monitors working on the electrochemical
principle are operated based on diffusion of
chlorine gas into the sensor which results in
the production of an electrical signal
proportional to the Cl2concentration.
It allows accurate measurement of even low
concentrations, which is essential in chlorine
monitoring in the ambient conditions.

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All you need to know about Chlorine (Cl2)OIZOM’S PRINCIPLE
Oizom’s ODOSENSE is the real-time odour
emission tracking solution. It continuously detects,
measures and monitors the odourful gaseous
contaminants including H2S, NH3, SO2, CH3SH,
TVOC, Cl2, CH2OH, and weather parameters like
temperature, humidity, wind speed, and wind
direction.
The sensor that measures Cl2 work on the principle
of electrochemical sensing.
Real-time monitoring of Cl2 helps in
determining the source of odour as well as
formulating an action plan to control emission of
chlorine.