A. Do not work in a malfunctioning hood.

Figure 17.1
Left: Hood marked out of service until repairs are completed.
Right: Example of EHS inspection sticker.

B. Check the EHS inspection sticker on the hood (usually on the sash) to ensure it has been inspected within the past 12 months. EHS measures the face velocity of all hoods annually, notes any deficiencies, and refers them to UNC Facilities Services for correction. Recommended face velocities are between 90-120 feet per minute (fpm).

C. Test the airflow alarm prior to using the hood to ensure it is operating properly.

Figure 17.2
Three common examples of hood airflow alarm devices.

D. Check the sash height.

  1. EHS affixes these stickers to vertical-sash laboratory hoods to remind users not to work with the sash above 18″. Try to keep the sash closed unless you are setting up or actively using the hood.
  2. You can raise and lower a correctly operating hood sash smoothly and with minimal effort. If you have difficulty operating the sash, or you cannot lower it completely, contact EHS. Do not place equipment, cords, tubing, etc. so that you cannot lower the sash quickly and completely.
  3. The recommended best practice for a combination sash hood (horizontal sliding panels within a vertical sliding sash) relies on completely closing the vertical sash while working through the horizontal sliders. Regular use of the horizontal sliding panels with the vertical sliding sash closed reduces chemical exposure and reduces energy expense. The vertical sliding sash should only be open during set up, not while manipulating objects in the hood with reactions present.

Figure 17.3
Combination sash hoods.
Left: Correct position of a combination sash while performing experiments.
Right: Only raise the vertical sash when setting up experiments.

E. Work at least 6″ into the hood to keep chemicals and vapors from exiting.

F. Do not work with your head breaking the front plane of the hood! Sashes at the proper working height generally create a physical barrier between the operator’s head and the inside of the hood. Working with your head in the hood often means that the sash is too high, or that the horizontal panels are opened too wide on a combination sash hood.

Breathing Zone
Breathing Zone at different working locations inside the sash.

Figure 17.4
Laboratory worker with his head between the horizontal sashes on a combination sash hood.

G. Take steps to maximize containment.

  1. Place blocks under large equipment to allow air to flow underneath the equipment.
  2. Keep the work area and bottom baffles clear from clutter.

H. Use chemical storage cabinets for long-term storage, not your hood. Items in a hood will impede and disturb the exhaust airflow and potentially reduce or eliminate the safety factor.

I. Reduce cross drafts, foot traffic past the hood, and quick movements in and around the hood. The recommended 100 fpm for hood face velocity is only a little more than one mile per hour (1.14 mph; 1.83 kph). Other sources of air movement can easily overcome this.

J. Remove electrical units or other spark sources from the hood when flammable liquids or gases are present. Do not place power strips or surge protectors in the hood. Plug in all electrical equipment outside of the hood.

K. The use of a laboratory hood does not negate the University policy on eye protection. Eye protection is required for all faculty, staff, students, and visitors in laboratories during experimental procedures that could produce liquid or solid projectiles.