Oil Spill Basics

Yearly spillage

Every year 100 million US gallons of oil spill. This is equal to 100 school gymnasiums: Typical school gymnasium = 45' X 45' X 66' = 133,650 cubic feet 1 cubic foot = 7.481 gallons Gym holds 999,387 gallons (almost 1 million gallons). The biggest spill ever occurred during the 1991 Persian Gulf war when about 240 million gallons spilled from oil terminals and tankers off the coast of Saudi Arabia. The second biggest spill occurred over a ten-month period (June 1979 - February 1980) when 140 million gallons spilled at the Ixtoc I well blowout in the Gulf of Mexico near Ciudad del Carmen, Mexico. But even all the oil spilled during the Persian Gulf spill is only about 1/3 of what the US uses in one day!

The Exxon Valdez spill in Alaska was approximately 11 million gallons. That spill was only about the 35th largest in the world, though it was the largest in the US. It came from a huge supertanker that was about the size of 15 gyms in length X 4 gyms wide X 2 gyms deep (which held 66 million gallons).

Why does all that oil spill?

We use a lot of oil and it needs to be transported. The US uses 710 million gallons per day. In fact, every 22 minutes, the US uses up what spilled in the Exxon Valdez spill. The world uses 2.73 billion gallons (2,730 gyms full) per day.

Every day 31.5 billion gallons of oil are at sea being transported. But not all spills come from tankers. Some comes from storage tanks, pipelines, oil wells, tankers and vessels cleaning out tanks.

What is all that oil used for?

  • Fuel (for transportation and factories)
  • Electricity generation
  • Machinery
  • Asphalt
  • Heating
  • Wax (crayons, candles)
  • Medicines
  • Ink
  • Plastics
  • Fertilizers
  • Pesticides
  • Paints/varnishes

How does it spill?

  • Accidents: often through carelessness
  • Sometimes unavoidable events: weather, earthquakes
  • Intentional spills: terrorists, war, vandals, dumping

What happens to oil when it spills?

Oil generally floats because it is lighter than water.

A good experiment to do here is to add vegetable oil, which acts like crude oil, to food-colored water in a large, clear plastic soda bottle with a cap. Shake it and watch how the oil always settles on top.

30-40% evaporates in the first 24-48 hours; these are the most poisonous (toxic) portions, as well as the portions that are the most soluble, and flammable.

Oil tends to float and spread out into a very thin film on the water surface...usually only about 0.1 mm thick...then spreads even thinner to a sheen, which is one tenth or one one-hundredth of this. Sheens are often seen as rainbow-like or silvery in puddles in parking lots.

It is very rare for oil to sink. It needs to adhere to heavier particles such as sand, algae, or silt to sink. An exception is a kind of oil used for burning in electric utility plants. This oil can actually sink in water since it is heavier than water.

What are the environmental impacts?

These impacts are very often grossly exaggerated in the public media. Environmentalist groups have been notorious in spreading misinformation about environmental effects. Nevertheless, oil can have a significant impact on marine larvae, birds and mammals in particular, and to a lesser extent on fish.

Some components of oil are toxic if exposure occurs within the first two days of a spill (1 part per million [ppm], i.e. one gallon in one million gallons, can be toxic to invertebrate larvae; 1000 ppm for fish). Oil on feathers hinders the water-repellancy of the bird. Oil on fur takes away its insulating capacities.

What happens after a spill occurs?

Response teams often protect sensitive areas with booms (floating barriers) and help oiled wildlife by cleaning birds and fur-bearing mammals with detergent. The most common cleanup techniques are outlined below:
  • Containment and recovery: Surround the oil with booms and recover the oil (for cleaning and reuse) with skimmers. Skimmers separate oil from the water by:
    • centripetal force -- water is heavier than oil and spins out further so the oil can be pumped out
    • lifting oil on a conveyor belt off the water surface; or
    • wringing out the oil that clings to oleophilic (oil-attracting) rope mops.
    This technique is the most widely used as it is least destructive, but it is only 10-15% efficient under even the best circumstances.
  • Sorbents: Remove oil with absorbent sponges made from diaper-like substances. Some sorbents are made from natural materials -- straw, grasses, coconut husks, or wood chips.
  • Dispersants: These are chemicals that act like detergents to break oil up into tiny droplets to dilute the oil's effect and to provide bite-sized bits for oil-eating bacteria that occur naturally, particularly in areas that have had a history of oil spillage.
  • Burning: Burning is usually 95-98% efficient, but does cause black smoke. The smoke is not more toxic than if the oil were burned as intended in fuels. One gallon of oil burned this way creates the same pollutants as three logs in a fireplace or woodstove.
  • Bioremediation: Enhancing natural biodegradation by natural oil-eating bacteria by providing them with needed fertilizers or oxygen.
  • Shoreline cleanup: High-pressure hosing to rinse oil back into water to be skimmed up. This usually does more harm than good by driving the oil deeper into the beach and by killing every living thing on the beach. This was used extensively after the Exxon Valdez spill due to public and state pressure to make the beaches "look clean again," despite the known risks. Areas left alone to be weathered by winter storms were shown to be cleaner and harboring more life than those cleaned by high-pressure washing. (Short term aesthetic considerations should not override the more basic longer term ecological considerations in rehabilitating a beach.)
  • Do nothing: Particularly in open ocean spills, cleanup is difficult and not efficient. Wave action and photo-oxidation (from sun) helps to break oil down.

Who else might be affected by an oil spill?

Fishing industry, resorts and recreation areas, water supplies for drinking and industry.

What about prevention?

Since cleanup after an oil spill is so ineffective and so difficult, and does not always fully rehabilitate affected areas, prevention is most important. Effective prevention plans might include:
  • improved piloting; training of ship and tanker crews
  • training of storage and pipeline facility crews
  • enforcing pollution rules at sea
  • building more spill-resistant vessels
  • maintaining vessels and pipelines
  • preparing for spill response through effective training, planning (contingency planning), and practice drills.

Information provided by: 
Oil Spill Intelligence Report, Arlington, MA, U.S.A.

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