Introduction

When oil enters the water from a source, such as a vessel, pipeline, or facility, it initially spreads out and forms a continuous or cohesive patch on the water surface. This layer or patch of oil absorbs energy and dampens out surface waves, making the area appear smoother or "slick" compared with the surrounding water. As the oil layer becomes thinner, it becomes more susceptible to being broken up by wave, wind, and current movement into smaller patches and narrow bands, or "windrows," oriented in the direction of the wind or current. Light oils, such as diesel and gasoline, may evaporate and disappear completely. Heavy oils, such as bunker fuels and crude oil, eventually spread out to form smaller, discrete patches or streaks, ultimately becoming tarballs.

The color, distribution, and consistency of the oil indicate the type of oil spilled, how long the oil has been on the water, and how readily it can be contained and/or recovered. You may be asked to observe these three properties and report them to the Incident Command. This aid is designed to help you characterize the oil and describe what you see in standard terms. The observations on which you should concentrate are the on-scene weather, the location of the spill, and the color and distribution of the oil. In addition, you might be requested to report other observations pertaining to the response that you notice while on-scene (e.g., the location of response equipment or the presence of wildlife).

Your choice of platform from which to make your observations--a helicopter, fixed-wing aircraft, or vessel--will be determined by a number of different factors. Each platform offers advantages and disadvantages:

• Aircraft, whether helicopters or fixed-wing, allow you a greater overview of the area affected by an oil spill. They allow you to reach the scene sooner and to investigate the outer edges of the area affected by a large spill.
  
• A helicopter can generally fly more slowly and at a lower altitude than can fixed-wing aircraft, allowing you a closer view of the spill.
  
• On the other hand, a vessel affords you an even closer look at the oil itself, giving you a better sense of its thickness and consistency. Taking a close look from a vessel also allows you to determine whether the reported spill is actually oil or a natural phenomenon that resembles an oil spill. Spawning herring, algae blooms, and jellyfish are often mistaken for oil. Finally, from a vessel you are likely to be able to spot tarballs that have formed during a spill. Tarballs are often not visible from aircraft.