Vapor Handling

Biological Safety Cabinets and Vapor Handling

Protection Against Vapors and Gases

All Class II biosafety cabinets are required to provide personnel, product and environment protection from particulate contaminants. There has been increased attention given to personnel and environmental protection from non-microbial chemicals, vapors and gases.

Distinctions between Type A1 and A2 and B1 and B2 cabinets are most dramatic when all types are subjected to tests for the presence of chemical vapors.

Regardless of cabinet Class or Type, it is important to remember that HEPA filtration traps particulates only, and is completely porous to gases and vapors.
It is essential that the user understand what happens to volatile chemicals inside different types of Class II cabinets. If vapors are used in a Type A cabinet not directly vented to the outside, vapors will pass freely through the exhaust filter into the laboratory.

Toluene Vapor Test Illustrates Differences

The chart on the right shows the location of toluene vapor generator (inches from front of work surface) in the Type A and Type B (total exhaust) cabinet.

In an effort to provide quantitative information about performance differences among the three Class II cabinet types, the Baker research laboratory has tested each cabinet with toluene vapor. Tests were conducted under strict experimental conditions using vapor concentrations higher than found in typical practice. All cabinets were vented to the outside.

Test Protocol

Liquid toluene was metered into each cabinet at a constant rate and dropped into a heated Petri dish held in a slanted position to flash evaporate the liquid to vapor.
The toluene vapor generator was moved from front to rear along the center line of the cabinet work surface.
Five replicate samples of vapor concentration in the downflow air were taken for each vapor generator position during each of four replicate runs on each cabinet.
All air samples were taken at a single location 8" below the diffuser at the work area center.
Evaporation of 1.8 ml/mm of liquid toluene at the work surface generated a continuous release of 1558 mg/mm of toluene vapor into each cabinet.

Test Results and Conclusions

The performance of different Class II cabinets is distinctly different when considering filtration, ventilation, air exchange, and airflow.

The airflow in a Type A1 or A2 cabinet is not well suited for work with hazardous vapors.
When even minute amounts of hazardous vapors are present, it is recommended that the Type B2, 100% total exhaust cabinet be used.
If vessels containing hazardous materials which may vaporize are placed in a Type B1 cabinet, the container should be placed toward the rear third of the work surface, but not so far back as to block the flow of air through the rear grille.

Test Result Summary

Toluene vapor test results illustrate distinctly different vapor return patterns for each cabinet type

Cabinet Type	Test Result
Type A Cabinet	Vapor concentrations in the downflow air reached a constant value which did not significantly change as the vapor generator was moved from front to rear of the work surface.
Type B1 Cabinet	Significant changes occurred as the vapor generator was moved from front to rear of the work surface. With the generator placed in front, the amount of returned vapor paralleled the performance of the Type A cabinet. With the generator placed in the rear, returned vapor paralleled performance of the 100% total exhaust cabinet (Class II, Type B2). The downward curve illustrates the variance in vapor concentration related to location from front to rear.
Type B2 Cabinet	In the 100% total exhaust cabinet, no air is recirculated and all vapor was removed.
Type A2 Cabinet	Vapor concentrations in the downflow air reached a constant value which did not significantly change as the vapor generator was moved from front to rear of the work surface.

For More Information on Class II BSC Air Contamination & Vapor Handling Testing

A detailed report, Comparison of Chemical Vapor Handling By Three Types of Class II Biological Safety Cabinets, is available from The Baker Company. Please contact us to request a copy.

The Baker Company has prepared a mathematical formula for determining the amount of vapor that would be recirculated under a particular application using other volatile chemicals. For a free copy contact The Baker Company.