Who's who in the oil spill response team (Crude oil spill off Changi East)

Based on the reports (check out my previous post for links) on this latest oil spill in Singapore waters, the response is run-of-the-mill. Floating booms, dispersants and skimmers are traditional methods to combat spills of all sorts but they have their limitations. And sometimes, they are plain inappropriate to use.

For example, in 2000 & 2001, 2 phenol spills occurred near Changi/ Pulau Ubin. (With such a high shipping traffic in our waters, spillage of chemicals and oil is inevitably common.) Floating booms were used then in an attempt to block off the spill. Being moderately soluble (read: much more soluble compared to oil) in water and slightly denser than water, DO NOT expect it to float on the water surface to be corralled by mere floating booms. Phenol will simply dissolve and disperse into the water column, possibly killing many marine organisms along the way. The good news is phenol is reasonably easy to decompose (yes, something toxic to us need not be so to bacteria) so it should be all gone in a few days.

All right, back to our current crude oil spill.

1. Floating boom

Extremely versatile devices. The inflatable types are especially easy to deploy. Other types can be linked together into various lengths to corral or block off an oil spill.

One limitation is of course certain chemicals do not float on the surface for floating boom to work their magic. Another is they do not work so well in rough sea and foul weather. Oil (or other chemicals) can simply be splashed over or pushed under the boom.

Figure: 1 possible type of floating boom

2. Dispersants

Dispersants basically contain detergent, solvent and other stuff. They are supposed to emulsify the oil into tiny oil droplets. Theoretically, this should allow better decomposition.

In the old days, we would be concerned about the toxicity of dispersants on marine life and their persistence in the environment. However, nowadays non-toxic and biodegradable dispersants are in widespread use. Nevertheless, they still have limitations. One: they are not so effective against heavy oils and weathered oils which are too tough to break up. Another common problem is the lack of adequate vehicles (boats, planes, helicopters) to discharge the dispersants, especially for large spills that cover a wide area.

One other concern: the way they work is a double edged sword. Small oil droplets do indeed facilitate decomposition but they also can be taken up by larger organisms more easily. Instead of just floating on the surface, the oil is now "dispersed" downwards where the marine life has nowhere to hide.

3. Skimmers

These are essentially boats fitted with devices to soak up the oil.

Figure: A skimming device dipped into oil. The moving belt is coating with a sorbent material. Upon reaching the rollers, the oil is squeezed out so that the sorbent can container to soak up a new batch of oil.

Figure: Skimming device fitted underneath a boat

Figure: Combination of floating boom and skimmer. The boom is towed between a barge (yellow) and a skimmer (red) which soaks up the oil trapped within the boom.

Figure: A common configuration. 2 barges (yellow) tow a floating boom. The oil collected within the encirclement is removed by a skimmer.

As you probably can guess by now, if the oil spill is huge, you are going to need lots of skimmers (and supporting logistics) to remove it. Similarly, the operation can be hindered by rough sea and foul weather.

However, despite the limitations mentioned, it is still BETTER to clear the oil while it is at sea. Once the oil comes ashore, the problems outlined above will seem like child's play. Labour, time and cost will balloon astronomically if beach cleaning is required.

* All figures are hand drawn by me. Please contact me if you want to use them :-)

What will happen to all this oil? (Oil spill off Changi East)

Work has been terribly hectic the past few weeks so please excuse me for my lack of posts.

But hearing about the oil spill (2500 tonnes of crude oil) off Changi East made me sit up to find out more. As usual, I depended on Ria's blog posts to bring me up to speed on this accident which is the latest in a string of similar accidents (see list compiled by Siva).

1. Any crude on our shores? (26 May)
2. Will the oil spill reach Singapore shores? (26 May)
3. Any crude on our shores? (25 May)
4. What is being done about the oil spill? (25 May)
5. 2,000-tonne crude oil spill off Singapore

The oil spill has apparently hit our shores despite earlier comments that it might vaporise before reaching land. The argument was being a light crude, the spill could vaporise easily.

So far, I have not seen any mention of exactly what kind of crude we are dealing with. Different crudes will have different compositions, affecting how a spill will behave and the remediation steps required.

Nevertheless, a crude oil should have the following fractions. Only the percentage of each fraction differs for different crudes.

1. Light fraction
   This refers to the low molecular weight compounds e.g. benzene which have a tendency to vaporise. Naturally, their vapours led to the petrochemical odour experienced in the eastern part of Singapore. In terms of marine pollution, these guys are of little consequence.
2. Water soluble fractionYes, some oily compounds are relatively soluble in water e.g. benzene. These are especially worrisome as they do not float on the sea surface but instead disperse both horizontally and vertically. (You are right if you deduce that living in the depths of the sea does not protect against these dangerous components.)
   
   Being water soluble, they are very bioavailable to marine organisms, easily entering their bodies through inhalation and ingestion. Oil booms have limited effect against them. On the other hand, being bioavailable makes them rather susceptible to decomposition.
3. Immiscible fraction
   These stuff do not mix with water. However, they can form emulsions (suspension of liquid particles in another liquid). Depending on the sea conditions, an oil-in-water emulsion or a water-in-oil emulsion may form.
   
   Oil-in-water emulsion means the oil is distributed into tiny droplets in the sea. This allows them to be more readily decomposed. BUT at the same time, these emulsified oil droplets are quite bioavailable and can disperse vertically, hence they are more likely to affect marine life.
   
   Water-in-oil emulsion commonly appears as yucky patches similar to chocolate mousse. These are tough for microbes to gobble up so they tend to remain in the sea for a long time.
4. Heavy fraction
   High molecular weight stuff like waxes make up this fraction. No surprise here - they are formidable for microbes to handle. They also tend to form "tar balls" - ugly pieces of black, viscous oil. These balls remain unchanged for a long time in the sea.
   
   Moreover, certain heavy compounds are literally that - HEAVY. They sink. Bottom feeders take note as the oil spill is no longer just restricted to the sea surface.

All the above considerations do not make oil spill response any easier. A good response will have to identify the kind of oil it is dealing with, accurately model the transport and fate of the oil and effectively manage adequate resources to combat the spill.