BOX 3.3 Elements of Institutional Policies Related to Hoods

  • Requirements for performance and containment

  • Density of hood use

  • Requirements for limitations affecting the ventilation system

  • Cost

  • Requirement for fume hood controls—occupancy sensors

may require 8 linear feet of working space to contain equipment and other experimental apparatus. The density of hood use in synthetic laboratories could approach a single hood that provides 6 to 8 linear feet of working space at the face of the hood for every 100 square feet of laboratory space. Benchmarking hood use in comparable institutions can be a valuable guide in selecting the type and the number of hoods.

Laboratory Ventilation System

The density of hood use will have a significant impact on the design of the ventilation system because of the large quantity of air that will be exhausted to the outdoors by properly functioning hoods. The ventilation system in chemical laboratories must satisfy two principal health-related objectives: occupational health, which is achieved through the proper installation and operation of chemical laboratory hoods, and occupant comfort, which is achieved by heating and humidifying the general laboratory air in the winter and cooling it in the summer.

A secondary function of the laboratory ventilation system is to prevent the migration of contaminants caused by incidental and accidental release of chemicals from the laboratory into other areas of the building. This is accomplished in part by providing single-pass air (air discharge from the laboratory directly outdoors) and in part by controlling the direction of airflow. The ventilation system should be designed so that air will flow from the areas with the least potential for contamination toward areas with the highest potential. Caution in setting system design parameters is important to ensure that safety considerations do not significantly increase cost. For example, a design requirement that the system should maintain designated pressure differentials rather than simply satisfy the objective of unidirectional airflow may substantially increase the cost of the project.

An enormous amount of energy can be consumed in conditioning the quantity of air that is delivered to laboratories to maintain comfort and ensure safe operation of the chemical hoods. Since laboratory air is not recirculated but instead is discharged as single-pass air, much energy is wasted. This problem is significantly exacerbated as the magnitude of hood use increases.

Fiscal responsibility provides a strong incentive to implement energy con-



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