Engineering controls are safety controls which are built into the area or system containing the hazard. Engineering controls often take the form of a physical barrier between the worker and the hazard or increased ventilation which remove the hazard from the breathing zone of workers.
General Laboratory Ventilation
Laboratory spaces should be negatively pressured relative to adjacent public spaces, such as hallways. This is to keep airborne chemicals and pathogens from leaving the laboratory environment and contaminating shared spaces. If you suspect that airborne chemicals or pathogens may be escaping your laboratory, contact EHS.
Ideally, negative pressure is achieved solely by general room supply and return air. In older spaces, a chemical hood may serve as the exhaust air for the laboratory. In this latter case, the laboratory may become positively pressured to adjacent spaces when the hood is shut off. If you see no return air ducts in your lab space this is likely the case and your hood should remain on whenever occupied or when experiments are underway.
Laboratory Chemical Hoods
All laboratories must provide an environment that is safe from fumes, vapors, dusts, and aerosolized microbes, carcinogens and radioactive materials that may be generated during an experiment. The purpose of any laboratory chemical hood (“fume hood”) is to capture the hazardous airborne material in an air stream of sufficient velocity to exhaust it safely out of the laboratory.
The chemical hood's face velocity, turbulence, and the worker movements are all important in preventing hazardous airborne material from reaching the breathing zone of the user. The face velocity is the linear air velocity at the opening or sash of the hood. The face velocity is affected by turbulence generated by the user at the opening, equipment and supplies inside the hood, drafts from doors, lab pressure differential, windows, and air vents in the laboratory - even people walking by the fume hood while it is operating. All of these factors must be managed.
The average face velocity of the fume hood with the sash positioned at the sash stop or at a height of 12-18” must be within the range of 80 to 120 ft/min.
- 80-100 for nuisance dust, noxious odors and low toxic materials.
- 100-120 for perchloric acid, carcinogens and high toxic materials.
Fume hoods should be kept closed to the smallest sash opening that still allows for adequate ventilation. The sash should be kept closed except when moving materials in or out of the fume hood. To properly use a fume hood:
- open the fume hood sash to its widest extent to place equipment or chemicals;
- close the fume hood sash to within twelve to fourteen inches of the base to allow placement of arms for manipulation of materials; or
- close fume hood sash to the base, slide horizontal sash to protect your face and body while allowing placement of arms for manipulation of materials.
- The bottom baffle should be open to exhaust heavier than air vapors that tend to settle and the top baffle should be open to exhaust lighter than air vapors that tend to rise. For most general laboratory fume hoods, both baffles should be open. Keep the openings free of obstruction by apparatus or containers.
- Do not work in a non-operating fume hood.
- Keep all apparatus at least six inches back from the face of the hood. Placing a stripe on the bench surface is a good reminder.
- Do not store chemicals or equipment in a fume hood.
- Clean up any chemical spills in a fume hood when they occur.
- Do not put your head in the hood when contaminants are being generated.
- Do not place electrical receptacles or other spark sources inside the hood when flammable liquids or gases are present. Permanent electrical receptacles should not be placed in the hood.
- Use an appropriate barricade if there is potential for an explosion or eruption.
- Observe static pressure gauges, velocity monitors or other operator indicators to insure that the exhaust system is properly working. In case of failure, notify your department head.
Testing and Maintenance.
Fume hoods are tested annually by EHS. Results are posted on the fume hood as well as reported to the department head. The velocity is measured at the center of square foot sections on the face of the sash with the sash open to its full extent or to the stops, if present. In addition, smoke is used to ensure that the entire face of the fume hood is exhausting out and not into the laboratory.
When Facilities repair personnel are called:
- Do not operate a fume hood when it is being serviced;
- Remove any chemicals or equipment from the fume hood before maintenance personnel perform servicing;
- Wash down the interior of the fume hood with soap and water before maintenance personnel work inside the fume hood.
- Maintenance personnel will put on personal protective equipment such as coveralls, goggles, gloves, and respirators when servicing your fume hood; and
- When maintenance personnel are working on the roof, you may be required to discontinue fume hood operations. If you are requested to do so, do not operate fume hoods.
Biological Safety Cabinets (BSC) are special hoods equipped with High Efficiency Particulate Air (HEPA) filter systems and designed to protect personnel and the environment from biohazardous material and protect the product from contamination.
Class I - a ventilated cabinet for personal and environmental protection, with non-recirculated airflow away from the operator. This class operates similar to a fume hood, except it may or may not be connected to an exhaust duct system. May be used for work with materials requiring biosafety level 1, 2 or 3 (BSL-1, 2, or 3) containment. Protects the user and environment but not the product.
Class II - a ventilated cabinet with an inward HEPA filtered airflow that protects the user, environment and product. May be used for work with materials requiring BSL-1, 2, or 3 biosafety containment.
Class III - a totally enclosed, ventilated cabinet of gas-tight construction. Operations in the cabinet are completed through attached rubber gloves. The cabinet is kept under slightly negative air pressure. Supply air is HEPA filtered and exhaust is double HEPA filtered or a combination of HEPA filter and incineration. May be used for work with materials requiring BSL-4 biosafety containment.
- Avoid the use of flammable gases or solvents in BSCs. Care must be taken to ensure against the concentration of flammable or explosive gases or vapors.
- Do not use open flames in BSCs.
- Ultraviolet (UV) lamps are frequently used in BSCs for supplementary decontamination of the work area. Use of UV lamps may help maintain disinfection, but should not be relied on for the sole disinfection of the work area. Thorough surface decontamination with an appropriate disinfectant is required. The UV light must be off when working in the BSC. The window sash must be completely closed when the UV light is on.
- BSCs must be tested and certified annually, after maintenance is performed, or after the unit is moved. EHS does not provide certification testing for BSCs, but can provide contact information for commercial certification companies in the area.
- Thoroughly understand procedures and equipment required before beginning work.
- Arrange for minimal disruptions in the work area while in use.
- Turn off the UV lamp when the using the cabinet.
- Ensure that the sash is set at its lowest position for work; this is usually marked on the sash frame.
- Turn on BSC light and blower.
- Check the air grills for obstruction and check pressure gauge.
- Wash hands and arms thoroughly with germicidal soap before working in the BSC.
- Wear proper personal protective equipment including a long sleeved laboratory coat with knit cuffs and over-the-cuff gloves, eye protection and respiratory protection, if appropriate.
- Wipe down all interior surfaces of the BSC with 70% ethanol or other suitable disinfectant and allow to dry.
- Load only materials required for the procedure into the BSC. Do not overload the cabinet.
- Do not obstruct the front, side or rear air return grills.
- Do not place large objects close together.
- After loading the BSC, allow several minutes to purge airborne contaminants from the work area.
- Keep all materials at least four inches inside the sash and perform all operations as far to the rear of the work area as possible.
- Keep clean and contaminated materials segregated. Arrange materials to minimize the movement of contaminated materials into clean areas. Keep all discarded contaminated material to the rear of the cabinet.
- Avoid moving materials or arms through the front access during use. Avoid techniques or procedures that disrupt the airflow patterns of the BSC.
- For spill response procedures, see Biological Spill/Release
Laminar Flow Hood or Clean Bench
A laminar flow hood or “clean bench” is for product protection only. Do not use for work with biohazard materials, volatile chemicals, toxic materials, or radioisotopes. The flow of air is towards the operator and the velocity of air movement can aerosolize materials on the unit surface, which presents a greater inhalation potential than work on a lab bench. Learn to distinguish the difference between this and a biosafety cabinet or chemical lab hood (fume hood).
There are myriad other ways to provide localized ventilation. These devices either capture the airborne hazard at the source of generation or they provide air movement away from the operator’s breathing zone. Some examples include: snorkels, canopies, vacuum systems, gas scavengers, downdraft tables, glove boxes, anaerobic chambers, and more.
EHS does not provide standardized guidance on these devices due to their variety. For testing, please contact EHS.
Gas cabinets are required for compressed gas cylinders or containers housing poison or pyrophoric gases. Interlocks, security measures, alarms, and ventilation of these unit and/or related laboratory are required. In some cases, the requirements may be met by housing the cylinder within an approved chemical lab hood (fume hood) if administrative controls are employed and documented to address power failures that compromise controls. Contact EHS for additional guidance prior to purchasing gases that require containment.
When machinery is present in labs, the moving parts present a physical hazard that may be easily overlooked in a setting possibly laden with other types of hazards (chemical, biological, radiation, etc.). Machinery-related injuries can be very severe and range from cuts to crushed hands and severed fingers or worse. For this reason, safeguards are required at all points on a machine that present a physical hazard. These include:
- The point of operation – where the machinery performs work on the material, such as cutting, shaping, or boring.
- Power transmission apparatus – all components of the mechanical system which transmit energy to the part of the machine performing the work, such as flywheels, pulleys, belts, connecting rods, etc.
- Other moving parts – all parts of the machine which move while the machine is working, such as reciprocating, rotating, and transverse moving parts, as well as feed mechanisms and auxiliary parts of the machine.
The safeguards against these mechanical hazards must meet the general requirements, but can take many forms:
- Prevent contact: The safeguard must prevent hands, arms, and any other part of a worker's body from making contact with dangerous moving parts.
- Secure: Workers should not be able to easily remove or tamper with the safeguard because a safeguard that can easily be made ineffective is no safeguard at all.
- Protect from falling objects: The safeguard should ensure that no objects can fall into moving parts. A small tool which is dropped into a cycling machine could easily become a projectile that could strike and injure someone.
- Create no new hazards: A safeguard defeats its own purpose if it creates a hazard of its own such as a shear point, a jagged edge, or an unfinished surface which can cause a laceration.
- Create no interference: Any safeguard which impedes a worker from performing the job quickly and comfortably might soon be overridden or disregarded. Proper safeguarding can actually enhance efficiency since it can relieve the worker's apprehensions about injury.
This section has been largely adapted from OSHA’s Machine Safeguards. See that manual for more information.