University Resources, Operations and Policies

 

Section 5


Section 5.0 Laboratory Chemical Hoods and Other Engineering Controls

Chemical safety is achieved by continual awareness of chemical hazards and by keeping the chemical under control by using precautions, including engineering safeguards, such as hoods. Laboratory personnel should be familiar with the precautions to be taken, including the use of engineering and other safeguards. Laboratory Supervisors should be alert to detect the malfunction of engineering and other safeguards. All engineering safe guards and controls must be properly maintained, inspected on a regular basis, and never overloaded beyond their design limits.


5.1 Laboratory Chemicals Hood Face Velocities
Chemical safety is achieved by continual awareness of chemical hazards and by keeping the chemical under control by using precautions, including engineering safeguards, such as hoods. Laboratory personnel should be familiar with the precautions to be taken, including the use of engineering and other safeguards. Laboratory Supervisors should be alert to detect the malfunction of engineering and other safeguards. All engineering safe guards and controls must be properly maintained, inspected on a regular basis, and never overloaded beyond their design limits.


5.2 Hoods Needing Repairs
Laboratory chemical hoods with face velocities below 60 feet per minute or above 150 liner feet per minute must be marked with a sign indicating that the hood should be repaired as soon as possible. This can be done online by contacting Facilities Management. Once the hood has been repaired, the CHO and Coordinator will need to be contacted to reevaluate the hood’s performance.


5.3 Safe Work Practices for Laboratory Chemical Hoods
When using a laboratory chemical hood, one must remember that the hood does not provide absolute containment or absolute protection from the materials in the hood. However, for most exposures, a properly designed room can provide adequate protections if certain work practices are followed. The work practices listed below are recommended by the American Conference of Governmental Industrial Hygienists in their text: “Industrial Ventilation: A Manual of Recommended Practices.” (17)

A chemical laboratory chemical hood cannot provide complete safety against all events that may occur in the hood, especially for toxic airborne contaminants with an exposure limit in the low part per billion ranges. For ordinary exposures, however, a properly designed hood in a properly ventilated room can provide adequate protection. Nevertheless, certain work practices are necessary in order for the hood to perform efficiently. The following work practices are required; more stringent practices may be necessary in some circumstances.

  1. All operations that may generate air contaminants at levels above the exposure limit must be conducted inside a hood.
  2. Keep all apparatus at least 6 inches back from the face of the hood. A stripe on the bench surface is a good reminder.
  3. Do not put your head into the hood when contaminants are being generated.
  4. Do not use the hood as a waste disposal mechanism except for very small quantities of volatile materials.
  5. Excessive storage of chemicals or any apparatus in the hood will impair the performance of the chemical laboratory chemical hood. Store flammable chemicals in an approved flammable storage safety cabinet. Store corrosive chemicals in a corrosive storage cabinet.
  6. Be sure that the switch is in the “on” position whenever the hood is in use and test hood often for airflow (for example using a Kimwipe).
  7. Using hazardous solids (powders) in hood may not be appropriate.
  8. Keep the slots in the hood baffle free of obstruction by any apparatus or containers.
  9. Minimize foot traffic past the face of the hood.
  10. Keep laboratory doors and windows closed (exception: some laboratories are designed for the laboratory doors to be open).
  11. Do not remove the hood sash or panels except when necessary for apparatus set-up. Replace sash or panels before operating.
  12. Do not place electrical receptacles or other spark sources inside the hood when flammable liquids or gases are present. No permanent electrical receptacles are permitted in the hood.
  13. Use an appropriate barricade if there is a chance of explosion or eruption.
  14. If hood sash is supposed to be partially closed for operation, the hood should be so labeled and the appropriate closure point clearly indicated.
  15. Where perchloric acid is heated above ambient temperature, vapor may condense within the exhaust system to form explosive perchlorates. In such instances, specially designed laboratory chemical hood exhaust systems must be utilized. These systems will have depicted exhausts and a water wash down system and may be used for perchloric acid digestions only.
  16. All laboratory chemical hoods should have spill protection lips (at front of the hood and for cup sinks located in the hood).
Any questions or request for assistance in evaluation of laboratory chemical hoods may be directed to the Chemical Hygiene Officer or Coordinator.

5.4 Flammable-Liquid Storage
Cabinets designed for the storage of flammable materials should be properly used and maintained. Read and follow the manufacture’s information and also follow these safety practices.

  1. Store only compatible materials inside a cabinet.
  2. Do not store paper or cardboard or other combustible packaging material in a flammable-liquid storage cabinet.
  3. The manufacture has established quantity limits for various sizes of flammable liquid storage cabinet and these limits should not be exceeded.

5.5 Eyewash Fountains and Safety Showers

  1. Equip all laboratories with an eye wash and safety shower. These must be located so they can be reached from any point the laboratory.
  2. Check the functioning of eyewash fountains and safety showers and measure the water flow at intervals. Promptly repair any facility that does not function properly.
  3. Be sure that access to eyewash fountains and safety showers is not restricted or blocked by temporary storage of objects or in any other way.

5.6 Respirators

  1. Laboratory personnel should wear respirators whenever it is possible that engineering controls or work practices could become or are ineffective and that employees might be exposed to vapor or particulate concentrations greater than the PEL, action level, TLV, or similar limit, whichever is the lowest.
  2. The requirements of 29 CFR1910.134 should be followed, indicating in particular:
    1. Written standard operating procedures governing the section and use of respirators.
    2. All employees who are likely to need to use respirators must be trained in their proper use, inspection, and maintenance.

5.7 Vapor Detection
Do not use odor as a means of determining that inhalation exposure limits are not being exceeded. Whenever there is reason to suspect that chemical inhalation limit might be exceeded, whether or not a suspicious odor is noticed, notify the supervisor. Laboratory workers should wear a respirator suitable for protection against the suspect chemical until measurements of the concentration of the suspect vapor in the air show that the limit is not exceeded. Under this circumstance and if there is no reason to anticipate an increase in the concentration of the chemical, and if the supervisor approves, the respirator can be removed and the work may continue.


Contact:

Joseph Landesberg, Ph.D.
Chemical Hygiene Officer
p – 516.877.4148
e – landesbe@adelphi.edu

 
 
 
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