Chapter 2 - Engineering Controls
2.0 Engineering Controls (Top)
Engineering controls are considered the first line of defense in the laboratory for the reduction or elimination of the potential exposure to hazardous chemicals. Examples of engineering controls used in laboratories at Cornell include dilution ventilation, local exhaust ventilation, chemical fume hoods, glove boxes and other containment enclosures, as well as ventilated storage cabinets.
The OSHA Laboratory Standard requires that "fume hoods and other protective equipment function properly and that specific measures are taken to ensure proper and adequate performance of such equipment." General laboratory room ventilation is not adequate to provide proper protection against bench top use of hazardous chemicals. Laboratory personnel need to consider available engineering controls to protect themselves against chemical exposures before beginning any new experiment(s) involving the use of hazardous chemicals.
The proper functioning and maintenance of fume hoods and other protective equipment used in the laboratory is the responsibility of a variety of service groups. Facilities Services and Engineering, Building Coordinators, EHS, and other groups service equipment such as fire extinguishers, emergency eyewash and showers, and mechanical ventilation. Periodic inspections and maintenance by these groups ensure proper functioning and adequate performance of these important pieces of protective equipment.
However, it is the responsibility of laboratory personnel to immediately report malfunctioning protective equipment, such as fume hoods, or mechanical problems to their Building Coordinator as soon as any malfunctions are discovered.
2.1 Chemical Fume Hoods
Fume hoods and other capture devices are used to contain the release of toxic chemical vapors, fumes, and dusts. Bench top use of chemicals that present an inhalation hazard is strongly discouraged. Fume hoods are to be used when conducting new experiments with unknown consequences from reactions or when the potential for a fire exists.
To achieve optimum performance, the greatest personal protection and reduce energy usage when using a fume hood:
Ensure the fume hood is working by checking the tell-tale (crepe paper hanging from hood sash) and air monitoring device if the hood is equipped with one. DO NOT use an improperly working fume hood.
If the fume hood is not working properly, let other people in the lab know by hanging up a Do Not Use Sign on the hood.
Work several inches inside the hood. This provides for the greatest amount of capture and removal of airborne contaminants. Also, do not place items on the airfoil or work with chemicals at the face of the hood.
Do not block the baffles at the back of the hood. These allow for proper exhausting of contaminants from the hood.
Keeping the hood sash lowered improves the performance of the fume hood by maintaining the internal vortex and containment. It also helps to conserve energy.
Keep the fume hood sash closed all of the way whenever the fume hood is not being used. Shut the Sash!
Do not use fume hoods to evaporate hazardous waste. Evaporating hazardous waste is illegal.
For work involving particularly hazardous substances or chemicals that can form toxic vapors, fumes, or dusts, the hood or equipment within the hood may need to be fitted with condensers, traps, or scrubbers in order to prevent the vapors, fumes, and dusts from being released into the environment.
Do not exhaust items, such as vacuum pumps, through the face of the fume hood as this will dissupt the airflow into the hood and may cause noncontainment. This will also not allow for the sash to be fully closed.
As with any work involving chemicals, always practice good housekeeping and clean up all chemical spills immediately. Be sure to wash both the working surface and hood sash frequently and always maintain a clean and dry work surface that is free of clutter.
In addition to annual fume hood inspection, face velocity testing, and dry ice capture testing, EHS also offers an online training program on the safe use of fume hoods. Additional information can be found in the Safe Fume Hood Use Guide.
2.1.1 Heating Perchloric Acid (Top)
DO NOT use heated Perchloric acid in a regular fume hood. If heated Perchloric acid is used in a regular fume hood (without a wash down function), shock sensitive metallic perchlorate crystals can form inside the duct work, and could result in causing an explosion during maintenance work on the ventilation system. Use of heated Perchloric acid requires a special perchloric acid fume hood with a wash down function. If you suspect your fume hood has perchlorate contamination or would like more information on perchloric acid fume hoods, then contact EHS at 607-255-8200.
2.1.2 Fume Hood Inspection and Testing Program (Top)
EHS and Facilities Services share the responsibility for the annual testing and inspection of fume hoods on campus. After each inspection, an inspection sticker is affixed to the fume hood. If your fume hood does not have an inspection sticker or if the existing inspection sticker on your fume hood indicates a year or more has passed since the hood was last inspected or for other questions please see the EHS Laboratory Ventilation page.
Fume hood testing and inspection consists of the following:
- The face velocity will be tested for compliance with American National Standards Institute (ANSI) and American Industrial Hygiene Association (AIHA) standard Z9.5-2012.
- A visual inspection using the dry ice technique from the ANSI/American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) standard 110-1995, will be performed in conjunction with face velocity measurements.
- Hoods will be classified as acceptable or unacceptable based on the average face velocity measurement and result of the dry ice test.
- If a hood is found to be unacceptable, a warning sign indicating the hood did not pass inspection and does not provide optimum protection will be attached in a conspicuous location. This information will be provided to the building coordinator who will follow through with the repair arrangements with other laboratories for the use of a different hood.
- A score will be taken based on the proper use and cleanliness of the hood.
||Hood on, used for a single chemical process or well organized multiple purposes
||Hood on, but empty or being used for storage
||Hood on, crowded or used for competing multiple chemical uses
||Hood on and contamination evident
2.1.3 Installation of New Fume Hoods (Top)
Installation of a new fume hood requires careful planning and knowledge of the existing building ventilation systems and capabilities. Improperly installed fume hoods or other capture devices can seriously disrupt the existing ventilation system and have a negative impact in the immediate room, other fume hoods, and the ventilation system throughout the building.
All fume hoods and other capture devices must be installed in consultation with Facilities Services, EHS. All new installations of fume hoods must comply with Cornell Design Standards and be commissioned by EHS to be included in the inspection and testing program. To request a new or relocated fume hood be commissioned please submit the following form: Fume Hood Commissioning form.
EHS can provide information regarding the selection, purchase, and inspection requirements for laminar flow clean benches, biosafety cabinets, and portable fume hoods.
2.1.4 Removal of Existing Fume Hoods (Top)
Any removal of fume hoods and capture devices requires prior consultation with your Building Coordinator, Facilities Services, and EHS. This is necessary to ensure building ventilation systems are not affected by removal of fume hoods and capture devices, and so utility services such as electrical lines, plumbing systems, and water and gas supply lines are properly disconnected. For more information about decommissioning of fume hoods, go to the Laboratory Ventilation page.
There is an additional concern for the presence of asbestos within the fume hood itself, and potentially in any pipe insulation associated with the ductwork and/or Mercury in cup sinks. Any asbestos must be properly removed and disposed of by a certified asbestos removal company. EHS can assist laboratories with the cleanup of any Mercury contamination. Contact EHS at 607-255-8200 for more information or questions about potential asbestos or Mercury contamination. See the Lab Move Guide in the appendix for more information.
2.2 Other Capture Devices (Top)
Engineering controls beside the fume hood include compressed gas cabinets, vented storage cabinets and local exhaust ventilation (LEV) such as capture hoods (canopy and slot), and snorkels. These work to capture and entrain chemical vapors, fumes and dusts at the point of generation. Examples where these devices would be appropriate are welding operations, atomic absorption units, vacuum pumps, work with dry nanomaterials and many other operations in the laboratory. Installation of any of these must be in the consultation of EHS and may include an engineering design to ensure the proper connection into the ventilation systems ductwork.
Glove boxes are sealed enclosures that are designed to protect the user, the process or both, by providing total isolation of the contents from the outside environment. They are usually equipped with at least one pair of gloves attached to the enclosure. The user manipulates the materials inside using the gloves. Typically, a glove box has an antechamber that is used to take materials in and out of the box.
Types of Glove boxes:
Controlled Environment (dry box) - These create oxygen and moisture free conditions by replacing the air within the box with an inert gas, such as nitrogen, argon or helium, depending on the type of materials to be worked with. A "rotary vane vacuum pump" is used to remove the atmosphere. Additional accessories may be used, such a gas purifier, to further reduce oxygen and moisture levels for particularly sensitive operations. There are 4 types of this type of glove box based on their leak tightness. Class 1 having the lowest hourly leak rate. This should be inspected by a service company during commissioning, when the gloves are changed, or when there appears to be a problem with the functioning of the glove box.
Ventilated Glove box (filtered glove box) - These have filters, either HEPA or ultra low particulate, on the inlet and outlet ends of the box and a blower to circulate the air. These provide protection to the user through this filtration and also if the exhaust is connected to building exhaust through a thimble connection. These can have serve in cleanroom applications by reversing the airflow in the chamber to positive pressure.
Regular maintenance and inspection is essential to ensure that a glove box is adequately protecting the user, the environment and/or the product/process. Routine maintenance procedures and the frequency of inspection (or certification) should follow the manufacturers and regulatory recommendations.
There are various tests that can be performed on glove boxes, the suitability of which depends on the glove box and the application. Tests may include pressure decay (for positive pressure), rate of rise (for negative pressure), oxygen analysis, containment integrity, ventilation flow characterization, and cleanliness. The source of a leak can be identified using a Mass Spectrometer Leak Detector, ultrasound, the soap bubble method or use of an oxygen analyzer. For an in-depth discussion of glove boxes and testing, see: AGS (American Glove Box Society) 2007 Guide for gloveboxes – Third Edition. AGS-G001-2007.
Please see other references at the bottom of this page for further details.
2.4 Water Protection in Labs (Top)
Laboratory personnel must ensure that any piece of equipment or laboratory apparatus connected to the water supply utilizes backflow protection or is connected to a faucet with a vacuum breaker. The purpose of backflow prevention and vacuum breakers is to prevent water used in an experimental process or with a piece of equipment from back flowing and contaminating the laboratory’s and building’s water supply system. Examples of situations that can result from improper backflow protection include chemical contamination and/or temperature extremes (i.e. hot water coming from a drinking water fountain).
Please see these other references used in this chapter for further details:
Gary Roepke, Bob Applequist. 2010. "A Primer on Glove boxes." Controlled Environments, October: vol 14. no. 9.
Louis J. DiBerardinis, Janet S. Baum, Melvin W. First, Gari T Gatwood, Anand K. Seth. 2013. Guidelines ofr Laboratory Design, 4th Edition. New Jersey: Wiley.
Ventilation, Committee on Industrial. 2010. Industrial Ventilation, A Manual of Recommended Practices, 27th Edition. Cincinnati: American Conference of Governmental Industrial Hygienists.