Tuesday, February 15, 2011

Understanding Ethyl Alcohol

This “Chemical of the Quarter” excerpt is from the U.S. Coast Guard Proceedings of the Marine Safety & Security Council magazine.

Ethyl Alcohol

What is it?
Ethyl alcohol, also known as ethanol or ethyl hydroxide, is the proper name for grain alcohol “spirits.”

Retail gasoline typically contains 10 percent ethanol.

How is it shipped?
In the U.S., ethanol is shipped almost exclusively in rail tank cars and in tank barges from the chemical plant where it was produced to the refinery or plant where it’s blended with gasoline. Additionally, large quantities of ethanol are shipped from one region to another on tank ships.

Ethanol is shipped and stored at ambient temperature and atmospheric pressure and, like gasoline and diesel fuel, is never heated prior to being pumped through a hose or pipeline.

Why should I care?
Shipping concerns.
Ethanol is a grade “C” flammable liquid, with a closed-cup (sealed lid) flashpoint of 55°F, meaning it can be expected to be above its flashpoint in warm weather (see endnote 1). Gasoline is always above its closed-cup flashpoint of -38°F, but automotive diesel fuel is almost always transported and stored below its 125°F closed-cup flashpoint. Therefore, the level of concern among transportation workers handling ethanol is midway between gasoline and diesel fuel.

Ethanol, like other alcohols, is somewhat corrosive. However, there is little concern for the structure of an ethanol-carrying barge or its pumps and piping because the tanks are inspected (for certification) by the Coast Guard and because ethanol is only mildly corrosive.

As far as the stability and seaworthiness of the vessel is concerned, it’s a physical impossibility to overload a barge because the specific gravity of ethanol is considerably lower than fresh water: 0.79 (at 68°F) vs. 1.00. The principal concern is for the flammable vapors.

Fire or explosion concerns. One characteristic of ethanol vapor that causes concern is the width of its flammable range (see endnote 2). Ethanol’s range, from 3.3 to 19.0 percent (by volume in air) is considered somewhat wide in comparison to gasoline’s narrow range of 1.4 to 7.4 percent. The wider the range, the greater the chance of a flammable mixture should a leak or spill occur. Since ethanol is heavier than air, its vapor spreads out downwind and downhill, hugging the ground or deck.

Health concerns. The short-term exposure limit is 1,000 parts per million (ppm). Exposure to a concentration of ethanol vapor of more than 1,000 ppm may cause headache and eye irritation. Exposure to ethanol vapor also causes dizziness, double vision, and other classic alcohol intoxication symptoms. A victim of vapor exposure should always be removed to fresh air.

What's the Coast Guard doing about it?
Domestic tank vessels are inspected and certificated under Title 46 of the Code of Federal Regulations, Subchapter “D” (rather than subchapter “O”) because alcohol has a relatively low danger threat. If an alcohol-carrying tank ship is of foreign registry, it must be issued the appropriate certificate of compliance by the Coast Guard.

Additionally, the Coast Guard monitors ethanol spill statistics. Over the past six years, there have been only two ethanol spills from tank vessels in the U.S. while loading or discharging, and they were both under five gallons. Waterfront facilities have averaged one spill a year, and only one of these spills has been more than 100 gallons.

1. Flashpoint: The lowest temperature at which the vapor can be ignited momentarily. A “closed-cup” (sealed lid) flashpoint tester with a low-mass thermocouple is used. In general, the closed-cup value is 10 to 15°F lower than the “open cup” value.
2. Flammable range: The range of vapor concentration (percent by volume in air) that will burn or explode if an ignition source is present. Limiting concentrations are called the “lower explosive limit” (LEL) and the “upper explosive limit” (UEL). Below the LEL the mixture is too lean to burn. Above the UEL it is too rich to burn.

For more information:
Full article is available at http://www.uscg.mil/proceedings/spring2010.

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