Understanding Chlorine

This "Chemical of the Quarter" excerpt is from the U.S. Coast Guard “Proceedings of the Marine Safety & Security Council” magazine, by Ms. Suzanne Chang, Chemical Engineer, U.S. Coast Guard Hazardous Materials Standards Division.

Chlorine

What is it?
Chlorine (CLX) is highly reactive and most commonly found combined with other elements, i.e. sodium chloride (table salt), sodium hypochlorite (bleach), and calcium hypochlorite (swimming pool chlorinator).

It is also one of the most essential chemical building blocks in manufacturing many household goods, such as polyvinyl chloride plastics, insecticide, refrigerants, sandwich wrap, carpeting, paints, and house siding.

How is it shipped?
Bulk chlorine is typically shipped as a compressed liquefied gas in tank cars, tank motor vehicles, and barge tanks.

For transporting by barge, the design of the barge is dependent upon whether it is used for inland river routes or for oceangoing routes.

Why should I care?
Shipping concerns. Since chlorine is shipped under pressure, one concern is maintaining cargo pressure. Depending on the capacity of the tanks aboard a barge, at least two pressure relief devices are installed into each cargo tank to prevent any over-pressurization.

Normally, dry chlorine does not corrode steel. However, wet chlorine is highly corrosive because it forms hydrochloric acid, so precautions need to be taken to keep the chlorine and equipment dry and atmospheric moisture out.

Health concerns. Chlorine gas is primarily a respiratory irritant and is highly corrosive when in contact with moist tissues such as the eyes and skin. The extent of damage caused by chlorine depends on the amount a person is exposed to, how the exposure occurred, and the duration of the exposure.

Chlorine can be detected by its odor (it smells like household bleach) at levels of 0.002 parts chlorine per million parts air (ppm). At 1.0 ppm, chlorine is a perceptible irritant. A level of 10 ppm is considered immediately dangerous to life and health—a person exposed to that level should seek protection at once. Continued exposure at that level could result in permanent damage or even death within as little as 30 minutes.

Fire or explosion concerns. Chlorine is not flammable or explosive. However, it is capable of supporting the combustion of certain substances, similar to oxygen. Also, chlorine may react readily with organic chemicals, sometimes violently and with the generation of heat.

What's the Coast Guard doing about it?
The U.S. Coast Guard enforces chlorine barge regulations and inspection standards under the regulations in 46 U.S. Code of Federal Regulations part 151.3.

The Coast Guard is also working with other federal agencies and local authorities to develop measures to protect people, property, and the environment in areas where chlorine barges transit.

For more information:
Full article is available at http://www.uscg.mil/proceedings/winter2009.

Subscribe online at http://www.uscg.mil/proceedings/subscribe.asp.