Safety and Design of Toxicology Laboratories

The proper design of a toxicology lab is more than process and people. There are significant strategies to consider in the design. Layout and planning for the safety of the occupants is essential but equally important is the design and implementation of supporting infrastructure. Understanding the requirements of toxicology laboratories and implementing new systems to monitor them can help meet the design demands that the toxicology process requires of the space while still saving facility costs and maintenance for the life of the facility.

Toxicology labs are exceptionally air intensive. The quantity of fume hoods and biosafety cabinets required in what can be a limited space has a significant impact on overall operational costs of a facility. Toxicology laboratories, as with most laboratory spaces sensitive to cross-contamination, should be designed with one-pass air. This means that all of the lab supply and ventilation air is exhausted out of the space through general lab exhaust or fume hoods, bench snorkels, and biosafety cabinets (if exhausted). Laboratory devices such as fume hoods require large amounts of air to be supplied in order to compensate for the vast amount of exhaust air required from the space. Inevitably the facility spends significant money and energy to condition this supply air and once this air enters the space, it is exhausted within a matter of minutes.

Before considering money saving solutions for energy efficiency, the laboratory must first be designed for the safety of its occupants. Fume hoods are the major line of defense in the utilization of chemical hazards in a toxicology laboratory. By definition, fume hoods are not energy efficient, but their inefficiency serves the purpose of safety.

Toxicology labs often require a large number of fume hoods and biosafety cabinets, and it is frequently difficult to find appropriate locations and layouts for these devices. From a safety and hood efficiency standpoint, it is important that hood locations meet certain criteria. Often fume hoods are ganged together side by- side at one end of a laboratory. While this is efficient with regards to exhaust ducting, it does not allow fume hoods to operate properly and may impart unsafe operating conditions of fume hood air flow. Another common laboratory layout places fume hoods face-to-face across an aisle way. Proper spacing for fume hoods placed side-by-side is a minimum 3’0” and optimally 4’0” from one another while placing hoods face-to-face requires an optimal distance of 9’0”.

The example illustrated in this article is the new toxicology laboratory for the Medical Examiner for the County of San Diego, designed by Crime Lab Design and currently under construction. The San Diego toxicology lab is designed for a future capacity of twelve scientists plus additional laboratory support personnel. In order to support this staffing, eight fume hoods and five biosafety cabinets have been designed for the space. As can be seen in the floor plan of the San Diego toxicology lab, the layout has a number of back-to-back hoods in island conditions in the middle of the lab with two fume hoods along the west wall. The back-to-back scenario lends itself to some efficiency in exhaust duct layout while not impeding proper hood operation.

From a safety standpoint, the mechanical approach to laboratory design has been to provide a prescribed number of air changes per hour to laboratory spaces including toxicology. This prescribed air change per hour approach eliminates the possible build-up of airborne contaminants in the laboratory. The flat rate of air changes is an attempt at a one-size-fits-all approach to mechanical design. In the toxicology lab for the San Diego Medical Examiner, current technology has been employed in the form of a Demand Control Ventilation (DCV) system. DCV uses a series ofCO2/HC(hydrocarbon) detection sensors to inform the building management system how many air changes are required, on a room-by-room basis, per hour based on real-time values of CO2/HC concentrations. This allows the air system to dial itself back providing less conditioned air into the space in times when it is not needed. Although a DCV system does have an associated up front cost, the system itself has been shown to pay back in facility savings within as short a time frame as one year.

Instrumentation rooms are critical to the function of toxicology labs. These rooms require additional infrastructure and design considerations. One design consideration is the need for periodic maintenance of analytic equipment requiring access to all sides of the instrument. One such method of access is service aisles; however, providing service aisles within the instrumentation room has a significant impact on available space and the overall size of the instrument room. Instrument carts docked into a fixed bench layout not only provide necessary access to the rear of the instrument, but also provide isolation of the instrument from surrounding bench top support equipment such as computers and printers allowing the instrument to be unaffected by surrounding vibration.

Heat dissipation is also critical to the design of an instrument room. The first line of defence is to capture heat directly at the output source before it has a chance to enter the room. It is important that this capture device be able to capture as close as possible to the output on the instrument without having a direct connection. Similar to a thimble or canopy connection, the capture device should also draw room air so that the laboratory exhaust system does not overwhelm the instrument fan unit. One common capture device is an exhaust arm (snorkel). Consisting of a movable and adjustable arm mechanism, a snorkel comes with hood types that are appropriate to instrument heat capture. Even with point source heat capture, instruments and supporting equipment will place additional heat loads on the laboratory. It is important for instrument longevity and functionality that the mechanical system for the room be sized adequately to maintain proper temperature in the laboratory with little or no fluctuation.

Last, vacuum pumps are often utilized in conjunction with toxicology instrumentation. While many laboratories locate pumps on the benchtop adjacent to the instrumentation, pumps should be housed in a pump cabinet. This allows the direct capture of heat and fumes as well as providing a quieter environment for the laboratory staff.

Toxicology laboratories generate significant safety and energy demands on a facility. The requirement by facility owners to reduce energy consumption while maintaining a safe environment for scientists remains strong. Building infrastructure cannot solve all the energy issues. Space programming, laboratory layout, and laboratory equipment all need to be reviewed with an eye to reducing energy in conjunction with a focus on safety. Bringing the entire design team of engineers, architects, and laboratory planners to the table at the planning stage of laboratory design will benefit the project and allow for toxicology laboratory facilities to be as energy efficient as possible.

Matthew Pettit, PE LEED AP is a senior mechanical engineer and Susan Halla is a Project Leader with Crime Lab Design, which provides full architectural and engineering services for forensic and medical examiner facilities worldwide.