Fume containment and forensics

by John Haugh, Managing Director, Air Science Technologies , info@airscienceuk.com

The development of specialist containment products for the forensics industry owes much to technological advances made in the design and manufacture of conventional filtration fume cupboards and downflow benches. Forensic professionals have a wide array of materials at their disposal when examining evidence from a crime scene — fine metal powders, chemical dyes and even a form of vaporous superglue. These all aid the cause of criminal detection, but they come with their own particular hazards and make safe containment a priority. Cross contamination is also a threat to the integrity of legal evidence, and this gives rise to a need for storage facilities that are clean, secure and tamper-evident.

This article examines the key issues to be faced within a forensic laboratory and illustrates some of the technical solutions that have been devised to help combine ease of use with safety and accountability. These solutions are now being applied to various items of forensic equipment including fingerprint workbenches, dye staining benches and evidence drying cabinets, as well as more recent introductions such as the portable field cabinet — effectively, a fume cupboard in a suitcase.

However, despite the relatively unusual nature of the applications, basic principles still apply. In a forensic laboratory, like any other, the designer and specifier assess the nature of the anticipated risks, the function of the equipment, environmental factors and the physical requirements of the technician, and they apply safeguards accordingly. In a branch of science in which the analytical process can, itself, become the object of intense scrutiny, a successful result is a product that facilitates safe and efficient handling of materials while preserving the integrity of evidence at all times.

Fingerprinting benches
Dusting items of evidence with fine powder is often the simplest and best known way of obtaining a discernable print, and in such cases, special workbenches are used to entrap any errant particles that would otherwise enter the working atmosphere. Usually a bench mounted unit, these downflow work stations (DWS) draw in air at a constant velocity (typically greater than 24.5 metres per minute), creating an airflow over a working platform that sucks particulates into the unit itself. Here, one or more filters see to it that the dust — which may be aluminium powder or some other material — remains safely contained and that only clean air is vented back out into the laboratory. As a result, technicians’ lungs and expensive laboratory equipment all remain safe from the effects of contact with airborne particulates.

Before going on to examine the other investigative forensic processes, it may be useful to consider how these containment units have evolved and why filter based systems appear to be the norm. Firstly, the use of self contained apparatus means that equipment can be installed quickly, without the need for constructing ducts or vents, and that it can be relocated or replaced without undue disruption. Secondly, forensic laboratories often share the same buildings as other law enforcement offices, and this tends to limit a laboratory manager’s freedom to commission major structural work. Finally, internal filters mean that air is circulated over a very small distance, so large, energyhungry air handling systems are rendered unnecessary.

These aspects of filtration based technology are beneficial not only to forensic departments, but also to schools, colleges and specialist medical units within hospitals, so it is perhaps unsurprising that their containment systems share many common traits. The DWS, for example, provides an easily accessible platform while preventing airborne matter from entering the laboratory. In addition to fingerprinting, these features also make it ideally suited for use in medical histology and pathology laboratories, where, in a larger table-top form, the DWS will contain formaldehyde vapours and other potentially harmful materials without hampering access to the body or other subject material.

Superglue cabinets
There are other parallels between conventional containment systems and modern forensics equipment. For example, in cases where dusting is unlikely to yield identifiable prints, an alternative technique using ethyl cyanoacrylate and special dyes can be employed.

Better known as ‘superglue’, ethyl cyanoacrylate can play an important role in enhancing fingerprints. Heating it on a hotplate produces fumes which, under special conditions, will bond with even very indistinct fingerprints on non-porous substrates. Subsequent staining with special dyes can then produce a clear and robust print. However, while the superglue vapour is an excellent material for identifying evidence, it is also very hazardous to health, so a high level of operator protection is required.
For this reason, the unit must take the form of a complete enclosure, similar in most respects to the kind of filtration fume cupboard seen in many medical and pharmaceutical laboratories. However, rather than allowing constant access via a sliding sash window, the glue cabinet has an automated facility which carries out the key tasks without direct user intervention. Once the evidence and a quantity of glue has been shut safely inside, the unit will automatically begin heating the glue while controlling the humidity, internal air circulation and purge cycle. Activated carbon filters contain any excess fumes and the cabinet will unlock when the process is complete.

Dye staining benches
Once the cyanoacrylate has bonded with the print, the item is then dipped in an ethanol based dye on a purpose built workbench. Dye staining benches, such as the one pictured here at the Fingerprint Laboratory at Merseyside Police headquarters in Liverpool, are designed to prevent the release of ethanol vapours without unduly restricting access. In many respects, the bench is similar to those used in hospital pathology departments. Air containment is achieved by the same means but instead of plumbing with standard spray hoses and nozzles, the forensics unit incorporates a polypropylene sink, a dye storage tank and a water tap for rinsing treated materials.

Protection of evidence
The technology used in forensic laboratories must also take account of the fact that evidence will often become the subject of legal scrutiny, so the transparency and accountability of all investigative operations must remain beyond doubt. This is a principle that underlies the development of the forensic drying cabinet — an enclosure that is designed to store evidence and protect against any threat of cross contamination.

Without very effective venting, the atmosphere of any laboratory will normally contain traces of many different chemical, organic and biological compounds, so items left exposed could easily become contaminated. This is critical in the case of legal evidence because, for an item to have forensic value, it must be possible to prove that materials found upon it came into contact with it before it was taken into the laboratory. If this cannot be proven, then it is unlikely that it would be admitted by a court.

As a result, law enforcement agencies now make extensive use of forensic drying cabinets. Items that are to be subject to chemical tests — such as for blood — need to be dried in a controlled environment, where they cannot be contaminated by airborne cellular materials and where they are secure against accidental or deliberate tampering. Consequently, they invariably incorporate door locks with tamper evident seals to guard against unauthorised handling. Like fume cupboards, they draw in air but in this case, a HEPA filter is fitted to the air inlet to prevent the ingress of particulates, biohazards and other potential contaminants.

This cleans the incoming air, which then passes over the item of evidence at ambient temperature, allowing it to dry slowly and without accelerating the decomposition of potentially significant residues. The air is then drawn into the exhaust system — first through a prefilter, which traps particulates down to a size of approximately 0.2 microns. The function of this pre-filter is to protect the main HEPA filter, which then traps approximately 99.997% of all pathogens and any remaining particles of 0.3 microns or larger. The air then passes through a carbon filter, which removes odours, and a secondary HEPA filter as a final treatment for the vented air.

Conclusion
The forensic laboratory imposes several constraints upon the equipment designer. Like any containment system, the apparatus must offer effective user protection, must be easy to use and must allow as much access as possible without compromising safety. Moreover, and unlike many conventional fume cupboards, storage units must also preserve the integrity of evidence by affording protection against tampering and against the materials present in the normal working environment.

These factors have required the development of purpose built forensic products, but the fundamental principles behind them remain essentially unchanged. Filtration-based systems are always likely to be quick and easy to install, but to ensure that they afford effective protection, all such equipment must be supplied with an accurate and reliable ‘low airflow’ alarm that provides an early warning of possible filter blockages or other failures.

Recent developments suggest a move towards more specialist forensic products, such as the portable field cabinet, which is the size of a suitcase and can quickly be installed at a crime scene. Greater flexibility and portability help to speed the analysis of materials that may degrade rapidly and also help to obviate the problems of cross contamination within the laboratory environment.