How much space does an evidence unit need, based on number of officers, items taken in, etc? This is a common question and a similar version was asked in a recent letter to JAPE from Kerstin Hammarberg, Property and Evidence Supervisor for Minneapolis (MN) Police Department. The answer has to be, "That depends!" Kersten was alert enough to add the caveat, "taking into account an established purging system." Indeed, with a highly efficient purging system, you can answer the question by saying "You don't need any more space than you have now!" 

Before panic takes over, an explanation is in order. Purging should allow a Property Room to purge as much evidence as it takes in. Assuming there is some old evidence that has survived since before the effective purging began, then there is some extra room that can be cleared for a future increase in items. 

Another restriction to that recommendation is that it must look at your "In" and "Out" statistics for as many years as you have them. If there is a significant increasing trend, then it is reasonable to compensate for that and assume a need for additional space in the future. It is also reasonable to assume that the increases in technology that allows DNA and other trace evidence analysis from items that in the past have never been considered evidence will increase the amount of items seized. 

A federal research report looking specifically at Crime Labs also has some input regarding Property Rooms. If you are interested in looking into an analysis of space needs, you should read this report. It touches on such items as ventilation that are very critical in Property Rooms. The entire report can be downloaded from http://www.ncjrs.org/pdffiles/168106.pdf.   The title is "Forensic Laboratories: Handbook for Facility Planning. Design". Construction. and Moving. It was prepared by the Office of Law Enforcement Standards, National Institute of Justice, and published in April 1998. The remainder of this article is a portion of the report dealing directly with the space issue. 

QUESTION: How can I get just a rough idea of how big my crime lab should be? 

ANSWER: Over the past 5 to 10 years the numerous forensic laboratories that have been designed and constructed seem to point to a space ratio based on area per staff member. This ratio for most new facilities tends to fall within the range of 700 to 1000 ft² per staff member. In "Forensic Sciences Progress 5" (Springer-Verlag, 1991), the ratio of 1000 ft² per staff member is offered as a recommended standard. This ratio refers to gross square feet, not net square feet, and therefore, accounts for a prorated portion of circulation corridors, mechanical rooms, toilet rooms, lobbies, etc., for each staff member. It must be understood, however, that this ratio represents only a very loose rule of thumb that can be drastically affected by a number of variables. For example, laboratories with large amounts of low occupant space, such as evidence storage or vehicle examination bays, will unrealistically skew the ratio. The only way to fully and accurately assess space needs is through the Needs Assessment and Design Program process.