During my seminars on arson and legal sampling over the years, one fundamental question is asked a lot regarding the collection of samples for ignitable liquid residue (ILR) analysis for a potential arson investigation. That question is, "Do my samples really need ice for storage and transport to the laboratory?"

The people who ask this usually go on to describe how hot the fire was, that maybe the sample was collected when the sampling matrix was still warm; so why is ice needed?

The answer is simply yes.  Ice is needed.  It is needed for a number of reasons.

Why use Ice for Storing Samples?

Protect the sample from degradation.

By storing the sample in a cool environment, you are reducing the chances that the sample is degrading. For example, there are soil microbes that can consume some of the compounds used for ILR identification. By reducing the temperature, the microbial activity is reduced.

Prevent evaporative loss of the ILRs.

A stainless steel can in the hot sun gets warm. By putting a sample on ice, you reduce the temperature of the sample. ILRs are volatile, meaning they are trying to get into the air. In a previous blog, I discussed how stainless steel cans are not perfect for storage of fire debris. Reducing the temperature of the samples reduces cross talk of the samples.

Follow standardized protocols.

Most sampling guidance for ILRs suggests that samples be put on ice. Therefore, you are not following established procedures by not using ice.  

It demonstrates that you are following procedures and taking charge of your samples. No one will criticize you for putting your samples on ice. But they sure might criticize you if you don't. It may be portrayed as careless, or you may be accused of not following protocols if you don't.

It's only a couple of dollars to put your samples on ice, and it could break your case if you don't.