There are two primary reasons for wearing gloves while processing a crime scene. One is to protect us from the evidence and the other is to protect the evidence from us. In my previous post I discussed the first reason—protection from the evidence. In this post I will discuss the second reason—to protect the evidence from us.
To protect the evidence we wear gloves to avoid placing our fingerprints on evidence and to avoid cross contaminating the evidence.
Cross contamination is a real issue at crime scenes when evidence may include DNA. We don't want to place our DNA on evidence we collect and we don't want to transfer DNA from one item of evidence to another. For that reason we need to change our gloves often. When collecting DNA (such as swabbing a surface) we should change our gloves for each sample. When collecting evidence that may have DNA on it, we should change our gloves for each item of evidence.
Many investigators think that they can just wear one pair of gloves for the entire scene. The problem is an investigator is usually touching all sorts of things during the course of the investigation, such as tools, clipboards, notepads and pens. If the investigator uses a pen to fill out the property report or evidence tag, then collects the evidence, there is a possibility of cross contamination. First of all there was probably DNA on the pen the investigator brought to the scene. Using the pen and then collecting the evidence without changing gloves may result in the transfer of DNA from the pen to the evidence. Also, investigators will often scratch their face and end up with their own DNA on the glove before handling evidence.
Further, wearing one pair of gloves throughout the scene leads us back to the first reason we wear gloves-to protect us from the evidence. If we touch something potentially hazardous, such as body fluids, and then our pen, our pen is now contaminated. We take off our gloves and pick up the pen and now we are contaminated.
So remember to protect yourself and the evidence by not only wearing gloves in the crime scene, but by changing gloves before collecting each item of evidence.
One more thing: be sure the gloves you use are powder free. The powder in gloves can bind with the DNA you collect and interfere with the extraction and analysis of the DNA. And choose nitrile gloves if you are allergic to latex gloves.