A biohazard bag is a specially designed plastic or paper bag that is used to collect and transport evidence from a crime or accident scene to another site, such as the laboratory, where subsequent analyses can be done.
Samples such as blood , fabric, bullets, and other pieces of evidence cannot be analyzed at the scene. But if the transport to the laboratory alters the sample composition (i.e., contamination, decomposition ) then the value of the sample as a legally admissible piece of evidence is destroyed.
The use of a biohazard bag prevents such contamination of a sample. As well, in the case of a potentially contaminated or poisonous sample, the handler is kept safe.
Biohazard bags vary in their dimensions and capacity. Typical dimensions are 6 x 9, 8 x 10, and 12 x 15 inches. However, several features are often preserved. They are similar to the kitchen-variety sandwich bag, in having a "zip-lock" type of closure. This eliminates the need for an external enclosure and allows a bag to be closed when a handler is wearing gloves.
Similar to some household plastic sealable bags, biohazard bags can have plastic strips positioned above the zip-lock. They provide material that the user can grasp when opening the bag, without having to handle the actual storage area. This allows a bag to be easily and repeatedly opened, especially when the user is wearing gloves, and lessens ripping of the bag.
A common feature of biohazard bags is their rugged construction. In contrast to the single layered sandwich bags, biohazard bags can have three layers of polypropylene or other plastic polymer. This reduces the chance of leakage and puncture.
Most biohazard bags will have a roughened portion on the surface that allows for writing on the surface. Written identification of all retrieved evidence is essential. Bags can also have an external pouch to house related paperwork.
Sharp objects that could puncture plastic will typically be stored first in a paper bag or other receptacle instead of a plastic bag. Biohazard bags made of Kraft paper are commercially available.
The choice of paper instead of plastic can be advantageous in other ways. Paper allows a sample to remain dry during transport. In contrast, condensation that can form in a plastic bag transported at a warm temperature can be deleterious to, for example, blood-stained fabric.
see also Crime scene investigation; Evidence.