Understanding Primary Engineering Controls in the Lab

April 2019 - Vol. 8 No. 4 - Page #4

Primary engineering controls (PECs) are imperative tools in the clinical laboratory, but they are only as effective as the personnel who utilize them. Clinicians must understand how to properly work in a unidirectional flow environment to maximize the true function of these devices, and while PECs such as biological safety cabinets (BSCs) are certainly familiar to microbiologists, it serves the entire laboratory and clinical environment to understand the ramifications of incorrect use. Herein we will discuss some of the more important questions regarding PECs, how they work in a clinical setting, and what the clinical laboratory should consider when deciding to implement the use of a PEC in the execution of daily tasks.

What are the primary types and functions of BSCs?

BSCs, and PECs in general, are utilized for environmental protection, personnel protection, product/material protection, or for any combination of these safeguard factors. A Class I BSC is an example of a PEC designed for environmental and personnel protection, but not product protection, as the incoming air is not filtered before it hits the product; only the exhaust is filtered.

Class II BSCs that are not externally vented are an example of PECs designed to protect product and personnel. There are multiple types of Class II BSCs that differ in the amount of air that is recirculated within the cabinet and the manner in which this process is accomplished. Because the air from Class II BSCs can be exhausted back into the room, hazardous materials should not be used in these cabinets unless the exhaust is externally vented. When partially or fully externally vented, Class II BSCs provide product, personnel, and environmental protection.

Class III BSCs offer the highest level of environmental and personnel protection. This type of cabinet fully contains hazardous materials and is gas tight. They offer a high level of product protection as well, but all processes must be performed through arm-length attached gloves, which requires training and practice for full competency.

What departments in the clinical laboratory are most likely to utilize BSCs and other similar PECs?

In general, any clinician or laboratorian working with any level of biosafety or hazardous material(s) or performing any aseptic processes should be working in one or more of the various types of PECs. Certainly, any clinical microbiology laboratory will utilize PECs; BSCs are also commonplace in many clinical chemistry labs.

What is important for technicians to know about airflow types and their impact on the product?

Understanding the impact of airflow direction and the reasons behind the airflow design in any laminar flow device is critical. Horizontal flow hoods or work benches have filtered, supplied air being pushed across the work surface from the rear of the device toward the opening of the unit (and the technician using it). These devices are designed primarily for product protection and cannot be used for hazardous operations.

When working in a horizontal flow device, it is important to realize that the first air is directly behind the products on the work surface and technicians should take care to work directly in front of or above the products to ensure the first air is not blocked or contaminated. Dirtier items should be kept toward the front of the device off to a designated area and cleaner items toward the rear. All items on the work surface can cause turbulent air flow and create dead space directly in front of the supplies and between the supplies and the technician. To ensure no critical operations are performed in this space, study the visual airflow pattern via smoke testing, conducted by the device certifier.

Vertical laminar flow devices are more common in clinical labs and comprise a wider variety of PECs including workbenches, fume hoods, BSCs, isolators, et al. Vertical laminar flow can be used for hazardous testing if the exhaust is properly externally vented and/or filtered as required. Vertical air flow is typically less turbulent than horizontal and causes less cross contamination. The flow of air mimics gravity as filtered supply air is pushed from top to bottom, and then front to back over the work surface. Thus, first air is between the filter face and directly above the products and supplies on the work surface. Technicians working in these devices must minimize actions directly above the products and should never work above open containers.

What are the most important points to consider for effective use of a device?

Regardless of flow type, there are a few key factors to keep in mind at all times:

  • Always purge the PEC before use. Unless the fan is kept on at all times, a minimum 15-minute purge time is necessary to rid the work area of possibly contaminated air and refill the device with clean air.
  • All necessary supplies should be placed in the PEC before starting work. Do not overload the work space and include only what is necessary to complete the task in the device.
  • Wear all necessary personal protection equipment (PPE) as required for the task to be completed and avoid moving in and out of the device once work has begun.
  • Work as far back in the PEC as possible; unless the PEC is an enclosed system, the cleanest air will be farther back in the device, away from any openings in both horizontal and vertical flow devices.
  • Use slow and purposeful movements when working in the PEC, which will help to decrease particle shedding and avoid disrupting unidirectional airflow.
  • Work from clean to dirty and have a designated area for clean supplies and dirty supplies established before beginning the task. If working in a horizontal flow PEC, avoid placing dirty items behind clean supplies and in a vertical flow, avoid placing dirty items above clean ones.

What are some common user errors that occur during PEC use?

Forgetting or mistaking the nature of the device’s unidirectional airflow is a common route to error. If a technician is working directly above a patient sample in a vertical flow device, any contamination from the technician, the supplies, or the processes being performed will be pushed onto the sample via the downward airflow. Likewise, if too many large items are placed in a horizontal flow device, the airflow will become more turbulent, and proper first air will not reach the direct processing area.

Insufficient purge time when using a BSC can be problematic. When the fan is initially turned on, a minimum of 15 minutes must transpire, but technicians should also allow at least an additional five-minute purge time after all supplies have been placed into the cabinet before starting any testing. This allows the system to circulate clean air and remove any particles that might have been introduced via the supplies/products or been disturbed from the act of placing the supplies in the cabinet. Note that isolators or Class III BSCs with pass-throughs will have additional purge time requirements that must be followed.

Other common user errors include not thoroughly cleaning the device before and after use. All technicians need to be trained on how to properly clean the PEC. (Information on proper cleaning and disinfecting processes, and cleaning materials selection will be addressed in a subsequent article.) In addition, a common source of error is improper use of PPE. Some clinical labs use a single PEC for multiple processes, yet these processes may require different levels of PPE. All technicians who perform specific testing must be trained on both proper testing procedure and required PPE. Proper type and use of PPE is integral to many processes performed in PECs and should not be considered negotiable.

What user safety concerns should be taken into account?

Assuming that the most suitable PEC for the required testing is being used, has been installed correctly by the appropriate engineer and certified, respectively, there should be minimal safety concerns for the user. That said, the laboratory manager and the certifier should ensure the PEC sash is adjusted such that technicians can access the device while sitting comfortably. Simple as it may sound, an appropriate adjustable chair should be used that provides proper posture support. Correct posture while using these devices is important, as some processes can be labor intensive and require more than a few hours to complete. To avoid problems such as repetitive stress injuries, proper physical support is necessary.

Technicians should clean the PEC work surface before and after use, especially when working with hazardous chemicals/agents. Management should ensure proper cleaning reagents capable of removing all potential hazardous residues are in use and are evaluated frequently for efficacy and efficiency. As always, documentation of these activities should be performed.

Many PECs utilize safety alarms, which should be set appropriately, and all technicians should be trained on what the alarms represent and how to respond in the event an alarm is triggered. No alarms should be silenced or ignored. If an alarm triggers during testing, the technician should stop working at the next safe and sensible step and notify lab management.

During use, ensure all intake grilles in the PEC are clear of obstruction and that users do not rest their forearms on the grilles located under the sash in most Class I and Class II BSCs. All users of PECs should have pertinent work practices evaluated and cleared before use, and both initial and (at minimum) annual retraining should be performed and documented.

What information should laboratory directors and microbiology supervisors be aware of regarding proper maintenance of PECs?

Most clinical laboratories will have PECs and secondary engineering controls (SECs) recertified at least annually. Management should ensure this is performed at the appropriate intervals and should familiarize themselves with and be able to interpret the results. Performing thorough and theory-based training on proper PEC use for all technicians will help maximize the life of the PEC and if users are trained in how and why the device works, it will help foster proper use.

Comprehensive PEC cleaning includes establishing that the chosen cleaning reagents are not corrosive to the device surfaces. Train staff to avoid spraying alcohol or other reagents directly into the fan filter units or on interior surfaces; it is better to spray cleaning solutions onto sterile wipes, and then use the wipes to clean surfaces. If a spill of any kind occurs during testing, the PEC should be immediately and completely cleaned. Remove spill trays if applicable and ensure no residue is left in the intake grilles. If the sash is removed for cleaning purposes, ensure it is placed back in the correct position before use.

Implement a use log for the PEC to document any issues that may occur. The log should track who is using the device, time and date of use, and process being completed, and should prompt for cleaning before and after use. If the PEC has a magnehelic pressure gauge or other monitoring systems on the front of the device, technicians should document the gauge readings at time of use. These readings should not fluctuate by an established threshold between uses.

What factors should a clinical laboratory consider when choosing the appropriate BSC or unidirectional flow device for their needs?

The first factor to determine is what requires protection; the technician, the environment, the product, or a combination? If only the product needs protection, there are a multitude of unidirectional clean air devices/workstations that can be used. If the technician and the environment need protection, a Class I BSC may be sufficient. If all three are necessary, a Class II or III BSC or equivalent PEC would be needed.

The next important consideration is to analyze both the current testing and any future testing that may be in the pipeline. It is far more fiscally efficient to implement the PEC that a laboratory may need for future testing (that which potentially requires increased protective barriers), than simply satisfying its current needs.

Assess estimated volume and type of chemical vapors that may need to be contained. Will the vapors be contained within the HEPA or ULPA filters or will they pass through? What kind of external ventilation will be required, and is it feasible in the laboratory space available? More often than not, these are not concerns that clinical lab management will be able to resolve without both internal (eg, facilities engineering) and external consultation.

What should be considered regarding the physical placement of PECs?

There are several factors to consider when placing PECs and SECs, as equipment location often impacts unidirectional airflow and can create turbulence (eg, placement near a well-traveled area of the lab introduces turbulence via the passing of personnel). When deciding on location, consult a cleanroom engineer and/or the device manufacturer.

Exhaust requirements may seriously limit where PECs can be installed due to the need for power, ductwork, and filtration systems. Similarly, be sure all clearance requirements are met surrounding the device and incorporate filter location and ease of accession for future maintenance and repairs. PECs should not be placed such that ambient air supply inlets blow directly across the front opening of the device or directly onto any exhaust filters. In general, place PECs away from laboratory traffic patterns, doors, windows, sinks, and other PECs or air handler units.

How should the clinical lab respond to exceeded microcontamination levels in the PEC?

All clinical labs that utilize PECs should have a robust and routine environmental monitoring procedure in place that includes the necessary steps to take if an established level is exceeded. Implementing alert levels as well as action levels will aid supervisors in observing negative trends before an action level is triggered. When an alert level is hit, steps can be taken to decrease contamination without necessitating more drastic measures. Necessary steps can range from simple cleaning and resampling to shutting down the operations of that PEC until full remediation is established. The necessary steps should be determined by a risk assessment that investigates what processes are performed in that PEC and the direct risk to patients or other end users of the products or test results that culminate from those processes in that laboratory.


Primary engineering controls are extremely useful tools that, when used properly, can practically eliminate certain workplace hazards and significantly decrease the risk of user error. Training clinicians and other laboratory personnel to use these devices correctly is imperative, but explaining how and why PECs function should be part of any robust training program. There are numerous factors to consider when purchasing, installing, using, and maintaining clean-air devices, and expert consultation and thorough risk assessment should be incorporated into the decision-making process.

Erin Thane, BS, is a microbiologist servicing the clinical and pharmaceutical industries as vice president of Azzur Labs in Schnecksville, Pennsylvania—a contract microbiology laboratory focused on environmental monitoring programs, product testing, and training. Erin is an active member of the Parenteral Drug Association (PDA) and the Controlled Environment Testing Association (CETA), and she has volunteered as an SME/Grader for the CETA National Board of Testing (CNBT) RCP-SCCP exam since 2015.


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