When did you last read a material safety data sheet in detail?
A critical part of ensuring safe lab procedures, the writing in these documents typically manages to be both dry, yet extremely frightening, at the same time. Whether from chemical or pathological agents, the range of hazards discussed in material safety data sheets often involve airborne dangers to lab workers.
Regardless of the type of lab you work in – testing, university research, healthcare or manufacturing – ensuring safe air is crucial to avoid health impacts ranging from mild irritation to severe long-term damage and even death. Airflow controls have advanced rapidly in recent years, with specialty venturi valves and digital controls that may eliminate the spread of toxic fumes and pathogens, while reducing maintenance costs and conserving energy – in both positive, negative and switchable pressure environments.
The number of workers who are potentially exposed to airborne hazards is substantial. Just one subset of Canadian laboratories – testing labs – employs about 20,000 people in an estimated 2,700 facilities throughout the country, according to the Canadian Council of Independent Laboratories.
Airborne hazards in brief
Health & Safety Ontario’s “Laboratory Safety” sheet summarizes the various health and safety hazards from chemical and biological agents. The airborne dangers they list include both short and long-term health effects, such as:
- Respiratory system damage from inhaling toxic chemicals
- Irritation from acids and bases
- Asphyxia from cryogenic chemicals
- Infection and disease from viruses, bacteria and fungi
The University of Texas at Austin’s Environmental Health & Safety Department goes a step farther in specifying potential airborne hazards in labs. These include various compressed gases:
- Poisonous (chlorine, carbon monoxide)
- Reactive (ammonia, boron trichloride)
- Flammable (acetylene, ethylene)
- Inert (nitrogen, argon)
While the university describes the first three types of gases as being of “particular concern,” it explains that inert compressed gases also pose danger since they can cause asphyxia by displacing oxygen from confined spaces.
Specific hazards often present in hospital and biomedical research laboratories include toxic fumes from pharmaceuticals (such as cancer chemotherapy drugs – “antineoplastics”) and solvents for staining and processing tissues in pathology labs to help determine proper diagnoses for patients.
Clearing the air
One of the most essential components of laboratory safety is the facility’s engineering controls. “These types of controls are preferred over all others because they make permanent changes that reduce exposure to hazards and do not rely on worker behavior,” notes the U.S. Occupational Safety and Health Administration (OSHA).
To clear airborne hazards in laboratories, the engineering controls must fulfill multiple functions, including ensuring adequate ventilation and air exchange rates; filtering airborne contaminants; and maintaining appropriate pressure relationships between the laboratory and adjacent interior and exterior spaces. Notably, the airflow controls must provide negative pressure to contain pathogens in labs where such biohazards are present, while positive pressure is crucial in settings where the sterility of the lab is paramount.
Many laboratory workers are familiar with fume hoods, which exhaust airborne hazards from their immediate work area. Less visible are the room-level air handling systems that transport exhaust fumes outside the building and also ensure appropriate ventilation of the entire lab.
If you work in an older building, it is a safe bet that hidden in the ceiling are many units known as variable air volume (VAV) terminal units/boxes. Used in commercial and institutional buildings around the world, VAVs boxes are calibrated air dampers to control temperature and humidity into a designated space, and are still common in new labs being constructed today.
The basic operation of a VAV box involves temperature, pressure and sometimes occupancy sensors within a space sending signals to the VAV box controller. Within the VAV box an electric actuator positions a butterfly damper to control the volume of air passing into a space from the building’s heating, ventilation and air conditioning (HVAC) system. But, a number of manufacturers offer a higher performance alternative known as a venturi valve, which provides labs with quicker, more flexible, repeatable and accurate airflow control. Venturi valves do not require any scheduled maintenance and offer higher airflow turndowns, resulting in more room state pressurization flexibility, lower energy use and reduced maintenance – for operational cost savings.
Venturi valves operate based on the Venturi effect, a fluid mechanical principal named after the famed Italian physicist. The body of the valve is a tube with a constricted neck, for an overall hourglass-like shape. A cone assembly inside the valve responds immediately to changes in air pressure in the HVAC ducting, automatically adjusting to pressure changes.
Leaving aside a lengthy discussion of the physics of fluid dynamics and valve operation, this configuration provides a number of benefits in labs, as described below. (To see a demonstration of the inner workings of a venturi valve, many videos are available on YouTube, such as this one posted by HVAC consultant Belnor Engineering: https://www.youtube.com/watch?v=_7uhkeRNO-c).
Compared to traditional VAV boxes, venturi valves provide high accuracy airflow control due to:
- High speed of response, to both duct pressure and flow setpoint changes which cannot be matched by valves requiring flow measurement (g., VAV boxes and other alternatives) due to inherent signal latency between the flow sensor, controller and actuator.
- Mechanical pressure independence instantly maintains flow, even with constant changes in static pressure, so that a stable, reliable amount of directional airflow is not compromised. No movement of the actuator is needed, thereby extending the life of the entire assembly.
- Factory characterized flow metering technology that provides higher turn-downs to achieve a number of stable, accurate room pressure states. The cone assembly quickly moves into position to achieve the flow set point vs having to measure and find its position.
- Volumetric offset guarantees directional airflow. Zone balance controls for some venturi valves track each other, maintaining a design offset between supply and total exhaust to ensure directional pressure in the space.
Higher turndown ratios mean the device has a wider range over which it can accurately provide the correct airflow. With this improved accuracy, labs can better manage ventilation and maintain air pressure relationships for worker safety and research/testing/production integrity, regardless of room state (occupied, unoccupied or purge condition).
While worker safety is paramount when choosing laboratory airflow controls, many lab operators also select venturi valves for the operational cost savings they provide. Energy savings are based on cost reductions due to better management of conditioned exhaust. Operational savings result from no scheduled maintenance, as venturi valves do not use pressure transducers to measure flow.
To reduce energy consumption in a ventilation system, it is important to consider air flow. For example, to flow 1,000 cubic feet per minute (CFM) of air into a space, the facility designers could specify a 10-inch VAV terminal box or a 10-inch venturi valve. Based on the physics underlying the two valve types, a venturi valve can accurately exhaust as little as 50 CFM, compared to a minimum 250 CFM required from a VAV terminal box. Because a lab typically requires dozens of air control devices or more (depending on its size), and it costs a handful of dollars to vent each CFM, the energy cost difference between venturi valves and VAVs is substantial.
In addition to higher-than-necessary energy consumption costs, a traditional airflow control system using VAVs incurs high maintenance costs. If not properly maintained, the valve will not function as designed and can result in poor airflow control that reduces lab worker safety.
In its discussion of maintenance of lab systems, Health & Safety Ontario’s “Laboratory Safety” sheet notes the importance of “regular inspection and testing for airflow (proper velocities and volumes), duct work (free of corrosion, leaks and dents), and fans (working properly).” Regular maintenance of VAVs is crucial, as the valves’ butterfly dampers are susceptible to gathering lint and dust. In a facility with 500 traditional VAV terminal boxes, annual cleaning costs are on the order of $50,000 – $100,000. The design of venturi valves obviates this problem and the cost and hassle of regular cleaning.
You do not need to be an airflow control expert to play a role in ensuring that plans for lab construction – whether for a new building or a refurbished building – adequately address air safety. With the basic knowledge of airborne hazards and airflow controls discussed above, you have a starting point to ask the facility designers some intelligent questions to help ensure safe air for you and your lab colleagues.
Dave Rausch is the market manager for Phoenix Controls. He has more than 20 years of experience in the building industry, including engineering and product management roles in airflow controls and fire suppression systems. firstname.lastname@example.org