As we continue the exploration of design issues for forensic facilities, we will address room pressurization and air flow direction, improving facility operation and maintenance, and saving energy and resources. It is important to understand how and why architecture and HVAC system design must work together to develop a successful project.

As we continue the exploration of design issues for forensic facilities, we will address room pressurization and air flow direction, improving facility operation and maintenance, and saving energy and resources. It is important to understand how and why architecture and HVAC system design must work together to develop a successful project. In this article, Ken Mohr and Lou Hartman explore ideas and solutions for your engineering and architectural questions.

Maintaining a good indoor environment: The direction of airflow can be more important than the rate of airflow.

Let’s understand the basics. The total airflow rate for a laboratory is determined by how much air leaves (exhausted) vs. how much air comes into the lab (supplied). Airflow rate is usually measured by cubic feet per minute (cfm). If the total cfm is greater coming into a room, then the room is positively pressurized, or more air is being supplied than exhausted. If you opened the door to this room you would feel the air leave the room. If the opposite existed—more air is exhausted than supplied—then the room would be negatively pressurized. Again, if you opened the door to this room you would feel the air come into the room. Exhausted air could be through a fume hood device or an exhaust grill in the ceiling. Supplied air could be through a supply grill in the ceiling or through the door into the room. The amount of cfm needed for a room is determined by the number of exhaust devices (fume hoods, snorkels...), the amount of cooling (supplied air) required to help offset internal heat gains from people and equipment, or industry space standards of minimum ventilation rate requirements due to the activities in the room.

Any laboratory that uses chemicals or compressed gases requires a non-recirculating air supply system. The system is also known as a 100% outside air supplied system. This means all of the air that comes into the room is used and then exhausted; all of it. The opposite of this system would be a recirculating air supplied system—not all of the room air supplied would be exhausted, but reused in the same room or maybe by an adjacent room. Each room would be evaluated separately to understand the hazards present. As you can imagine, providing a recirculating air supply system would be less expensive to install and to operate. A space commonly overlooked for a recirculating system in a forensic lab is the Computer Forensics Unit.

Industry space standards tell us that minimum airflow rates are generally in the range of six to ten air changes per hour when the space is occupied. However, some spaces may have minimum airflow rates established by specific activities in the room or by internal facility management policies. A guideline often followed is one established by the National Institutes of Health recommending a minimum ventilation rate of six air changes per hour for an occupied laboratory. For laboratories where the amount of ventilation is determined by either equipment cooling requirements or exhaust device rates, it is common to recognize that all exhaust devices or equipment are seldom used at the same time. This creates a “usage factor” which is helpful in determining the entire size of the building’s HVAC system. Applying a “usage factor” in the design process of a forensic facility must be carefully analyzed to avoid under-sizing the ventilation system in the hopes of saving a few dollars.

The exhaust system must be controlled and coordinated with the supply air system to maintain the proper pressurization in each room as it relates to the surrounding rooms. The laboratory HVAC systems can either be constant volume or variable volume. A constant volume system is just that; the air is always moving at the same speed while a variable volume system has air moving at different speeds. This is best explained by the night set back. During normal facility hours of operation, the HVAC system is in one mode and at night the system is throttled back, still safe, but the demand is clearly reduced. Fume hoods may have their own exhaust fan, or may be manifolded and connected together to one or more common central exhaust fans. In general, a variable volume HVAC system with manifold exhaust is more flexible (ability to add exhaust devices), requires less ductwork, involves fewer pieces of control equipment, reduces the number of roof penetrations, and creates an opportunity for energy recoveryand savings.

Care needs to be taken when choosing the right external building exhaust and air intake locations to avoid drawing exhaust effluent into the fresh air supply and contaminating the building. The height of the exhaust stack must extend ten feet past the highest point on the roof, and the discharge velocity must fall between 3,500 cfm to 4,500 cfm to properly dissipate the exhaust plume.

Keeping it working: The right design solution can make facility maintenance easier.

Forensic laboratories by their very nature are complex buildings, incorporating systems and equipment not found in other types of buildings. Early in the planning process, the design team works closely with operations and maintenance personnel to gain their input and agreement on the design of building systems. The degree of sophistication of building systems needs to match the capabilities of staff responsible for maintaining the building. This logic can also be applied to the physical design of the facility, materials, and finishes, from the floors to the walls and the ceilings. Features that make forensic laboratories more easily maintained include:

• Centralized monitoring of critical freezers, face velocity of fume hoods, supply flows, and exhaust flows is useful for predictive maintenance of equipment and for ensuring safe operating conditions.

• Dedicated janitor’s closet in the Post Amplification DNA Lab prevents contamination of other cleaning supplies for the rest of the facility.

• Place high-maintenance items outside the actual laboratory to reduce disruption of laboratory operations and exposure of the maintenance staff to laboratory hazards.

• Plan for storage space. Did you know that most new construction project contracts include statements requiring the contractor to supply the project with extra materials (flooring, paint, lights, ceiling tiles...) for future repair or replacement?

• Scheduled preventive maintenance of equipment and periodic checks of air balance/directorial air flow.

• Proper selection of durable, attractive, low-maintenance materials. A brushed satin finish will not show finger prints like a polished finished.

Saving energy: Not only reduces your operating budget but has a positive impact on the environment

Historically, forensic laboratories consume large amounts of energy most commonly through the building HVAC system, due to the fact that most facilities require 100% exhaust systems. However, efforts to reduce energy use must not compromise the safety of the laboratory. Today, energy reduction concerns are not only within the building, but the energy used to make the material, delivery of the material, installation of the material, and disposal of the material after its useful life. This stream of material directly relates to “sustainability”—a method of harvesting or using a resource so that the resource is not depleted or permanently damaged. Any energy reduction strategy must be both appropriate and economically justifiable. Potentially viable energy reduction or sustainable measures that should be considered during the planning process include:

• Energy efficient lighting (reduces both electric used for lighting and air conditioning). Used in conjunction with natural light, a sensor can be attached to the light fixture that only allows it to come on when there is insufficient natural light.

• Reduce exhaust air requirements by using variable volume control of exhaust air through the fume hoods. Add a fume hood sash sensor to cause the sash to automatically close when not in use. A closed sash on a fume hood can cut the energy use by half.

• Use night setback controls to reduce the exhaust volume when the lab is unoccupied. Any of these options can have an override switch allowing for special operation.

• Rotary air-to-air energy exchangers or heat wheel technology captures the energy of exhaust air being discharged out of the building.

• Rain water could be captured and used to assist in flushing the toilets or assist in irrigation of the property.

• Energy recovery is also possible for hydronic systems associated with HVAC. Rejected heat from centrifugal chillers can be used to produce low-temperature reheat water.

Making sure it’s right: Testing the design solution is just another part of the building process

Commissioning is the process of validating not only the building systems, but also the facility design solution, and provides training to the occupants. The commissioning process starts at the very beginning with the understanding of the intended use of the laboratory and should include development of a commissioning plan, validation of individual components, and evaluation of the entire system. This requires verifying that the design meets applicable codes and standards and the building has been constructed in accordance with the design intent. Laboratory utility systems are the most obvious to be commissioned, not only to validate system comfort for building occupants, but in providing a safe and healthy work environment. It’s important that before the facility is turned over for use by the scientific staff, that proper system operation is verified and technicians, scientists, and maintenance personnel are trained and understand the systems’ operation. Commissioning the design means checking to see that goals and objectives of the laboratory were achieved, testing the true flexibility of the casework system, and educating the users on proper care and use of the furniture.


Hopefully you can see that good facility planning and the proper HVAC solutions result in good design leading to a successful forensic project. Modern forensic laboratories must meet many challenges: a secure facility, healthy environment, and a wide variety of sciences. If you are faced with the opportunity of planning a new or renovated forensic facility, please remember it is just as important to always ask questions and convey your expectations to the design team. Without your full participation the project will suffer; without the full coordination of architectural and mechanical challenges the project will also suffer. Only those working hand-in-hand can truly be successful.

Lou Hartman is a Principal and Sr. Mechanical Engineer with HarleyEllis, and Ken Mohr is a Principal and Sr. Forensic Laboratory Planner with HERA, Inc. HarleyEllis and HERA together form a strategic alliance called Crime Lab Design,which provides full A/E services for forensic and medical examiner facilities.