By Allan Goodman, Ph.D., and Robert Haugen, Ph.D., Flow Sciences
Flow Sciences has more than three decades of experience in designing, manufacturing and testing powder containment devices, predominantly for the pharmaceutical industry. These enclosures have evolved from small balance containment devices connected to remote blowers, to a variety of custom and standard products.
This increased product diversity has been achieved while maintaining the necessary features required for superior containment and airflow conditions conducive for enabling highly sensitive operations such as microbalance weighing and mixing and reacting chemicals.
No product reflects this sophistication more elegantly than the chemical fume hood. Originally designed around 350 years ago to contain accidents and prevent bad odors in the laboratory, the fume hood has become a device that can routinely produce control levels of vapors down to the part-per-billion level. This is particularly important because many researchers may be unaware of the toxicity or even the identity of chemicals routinely produced in experimental chemical reactions.1
In the United States, the primary containment measurement methodology for fume hoods since the late 1970’s has been ASHRAE 110. The latest version of this test, ANSI / ASHRAE 110-2016, uses an SF6(g) diffuser and mannequin with air sampler to determine a tracer gas presence in the breathing zone of a mannequin.2 A limitation of the ASHRAE test is that it is mostly static in nature and, other than the Sash Movement Effect (SME) component, involves no human interaction. In spite of these limitations, most manufacturers of fume hoods sincerely believe that containment of SF6 gas under the ASHRAE test conditions is a reasonable predictor for particulates as well as vapor containment.
This argument remains unconvincing for many of our customers. Indeed, many industrial hygiene organizations and personnel have not recommended the use of fume hoods for powder manipulation operations of any kind. It is therefore necessary to find new tests which quantify performance and limitations for fume hoods in the context of finely divided powders.
We have therefore chosen here to meld existing techniques centered around ASHRAE 110 with widely-accepted particulate containment measurement techniques4. This combined regimen was then directly applied to a 4’ fume hood so results of all tests could be compared with each other. If results were found to be consistent, a new combined test using all three phases of matter could be established.
The test results obtained here allow us to make some rather positive preliminary conclusions in this regard.