Middlebury

 

4. Engineering Controls

 

4.1 Purpose

Engineering controls are devices and equipment installed in the laboratory that are intended to minimize worker exposure to chemical and physical hazards. These controls must be maintained in proper working order for this goal to be realized. Faculty, staff, and students are to familiarize themselves with the use of the engineering controls in their labs, and to follow proper work practices when using these controls.

4.2 Modifications

No modification of engineering controls by Facilities Services or laboratory personnel is permissible unless testing indicates that worker protection will continue to be satisfactory.

4.3 Improper Function

Any failure or improper function of an engineering control must be reported immediately to the Chemical Hygiene Officer or the Director of Sciences Support Services. The system will then be taken out of service until proper repairs have been performed.

4.4 Laboratory Fume Hoods

Use of a laboratory fume hood is recommended for any work with volatile chemicals. A fume hood is to be utilized for all chemical procedures which might result in release of hazardous chemical vapors, mists, or dusts. As a general rule, the hood shall be used for all chemical procedures involving substances which are appreciably volatile and have a Permissible Exposure Limit (PEL) less than 50 ppm, or where exposure by inhalation is likely to routinely exceed the ACGIH Threshold Limit Value (TLV) or other action level for that chemical.

The following work practices apply to the use of fume hoods:

The user must confirm adequate hood ventilation performance prior to opening chemical containers inside the hood:

The hood’s face velocity monitor will display a green light, and the numerical display will indicate a face velocity of between 80 and 150 linear feet per minute.

Under some circumstances, it is possible that the numerical display may simply indicate “FLO.” As long as the green light is also displayed, this means that a suitable minimum flow rate, as determined by Siemens Building Systems, has been achieved.

As an additional check, an inward flow of air may also be confirmed by holding a strip of paper at the hood face opening and observing the movement of the paper; however, the controller display must also indicate one of the two safe operating conditions described above.

If the above conditions are not met, or if there are any other indications of a problem, do not use the hood! Instead, immediately notify the Chemical Hygiene Officer or the Director of Sciences Support Services about the problem.

Keep the sash of the hood lowered at all times except when making adjustments to apparatus within the hood. This is to prevent vapors from spilling out of the hood, and also to provide containment in the event of a vigorous or runaway reaction.

Hoods should not be used as a storage area for chemicals, apparatus, or other materials. Items inside the hood should always be kept to a minimum, and should be limited to the chemicals, apparatus, or other items being used in the immediate procedure.

Minimize interference with the inward flow of air into the hood by keeping apparatus and reagent bottles at least 6 inches (15 cm) back from the hood face, and ensuring that the exhaust slots at the rear of the hood are not blocked.

Hoods are not to be used as a means of disposal for volatile chemicals.

Prior to the introduction of new chemicals, the supervisor will determine that the hood to be used will offer adequate protection to the user.

The ventilation system shall be inspected regularly by Facilities Services. The hoods shall be inspected and tested at least annually to verify operation of the control system and to confirm that the face velocity is between 80 and 150 feet per minute. A copy of the records for all hood inspections shall be provided to the Director of Sciences Support Services.

4.5 Biological Safety Cabinets and Laminar Flow Hoods

The term “laminar flow hood” refers to any device designed to maintain a clean environment inside the cabinet. Many such devices offer no protection to the user from microorganisms or other pathogens, and are properly referred to as “clean benches.” A laminar flow hood designed to contain pathogens within the unit, so as to minimize the chance of exposure from these agents to the user, is referred to as a biological safety cabinet (BSC). Important! Because these devices exhaust air directly into the room, they do not offer any protection from hazardous or toxic chemical vapors or gases.

Biological safety cabinets are not to be used with flammable or volatile toxic chemicals. These types of materials are to be used only in a fume hood, if a hood is required.

A clean bench is to be used only with non-hazardous materials such as nutrient broths or growth media.

The supervisor shall determine when and whether a biological safety cabinet or a fume hood is appropriate for the operation to be performed.

4.6 Glove Boxes

Glove boxes are typically used for work with air-sensitive materials.

The exhaust gases from a glove box in which extremely hazardous substances have been used must be passed through scrubbers or receive other treatment as necessary before being released into the regular fume hood exhaust system.

For other substances, the exhaust gases from a glove box shall be discharged directly into the fume hood exhaust system.

4.7 Storage Cabinets

In the Laboratory Stores, any flammable materials will be kept in one of the designated Flammable Materials Storage Areas.

In individual laboratories, large quantities of flammable liquids are to be stored in an approved flammable materials storage cabinet.

In individual laboratories, it is recommended that large quantities of corrosive substances be stored in a corrosive materials storage cabinet, taking care to separate acids and bases.