Proper ventilation is required in histology laboratories to reduce the possibility of exposure to chemicals lingering in the air. There are a variety of standards for ventilation, from the various regulating agencies. OSHA’s is expressed as part of the 1990 Occupational Exposure to Hazardous Chemicals in Laboratories standard, commonly known as the Laboratory Standard; the same standard that requires the creation of a chemical hygiene plan.
OSHA’s requirements are pretty broad, basically just saying you need a system that provides a source of air for breathing (yes, air to breathe is always good in a workplace), and that the air should be flowing to prevent build up of toxic substances.
“General laboratory ventilation. This system should: Provide a source of air for breathing and for input to local ventilation devices (199); it should not be relied on for protection from toxic substances released into the laboratory (198); ensure that laboratory air is continually replaced, preventing increase of air concentrations of toxic substances during the working day (194); direct air flow into the laboratory from non-laboratory areas and out to the exterior of the building (194).”
It also sets a broad room air change rate at 4-12 exchanges per hour. Air change rate is the rate at which air in a space is recycled, so the higher the number, the more frequently air is being cycled through, reducing exposure to any contaminants that might be in the air. You can do the math on air change rates if you’re so inclined, by taking the amount of air flowing in (measured in cubic feet per minute) x 60 / room volume.
Air change rate is not normally something your everyday person on the street would know much about, but it became a subject of conversation in 2020 as concerns over the spread of COVID indoors dominated the news.
In addition to OSHA, the American National Standards Institute provides more recent standards (2012), which say, “Dilution ventilation shall be provided to control the buildup of fugitive emissions and odors in the laboratory. The dilution rate shall be expressed in terms of exhaust flow in negatively pressurized laboratories and supply flow in positively pressurized laboratories.”
So that begs the question, what is the difference between a positively pressurized laboratory and a negatively pressurized laboratory.
A negatively pressurized room has lower air pressure inside the room and will suck air into the room when doors and windows are opened, which keeps any contaminants from escaping outside the room. Positively pressurized means that there is a higher pressure inside the room, and air will leave the room without circulating back in.
The ANSI Standards caution that ventilation is a method for controlling exposure, but contaminants should be identified and controlled at the source. Dilution ventilation alone is not effective, and fume hoods should be used to minimize exposure at the source. This standard provides a suggested air change rate of 4 to 10 exchanges per hour.
To learn more about laboratory ventilation, check out NSH’s QLS Prep Course, a safety course designed to prepare you for the ASCP QLS exam.
References:
https://airinnovations.com/negative-positive-pressure-rooms-hospital-infection-control/
https://webstore.ansi.org/Standards/ASSE/ANSIAIHAASSEZ92012-1451471?source=blog&_ga=2.113976647.1563948570.1625747591-1101370899.1625747591
https://www.ncbi.nlm.nih.gov/books/NBK55875/#:~:text=General%20air%20flow%20should%20not,)%20(200%2C%20204).
https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.57
https://ehs.stanford.edu/manual/laboratory-standard-design-guidelines/ventilation-considerations-biosafety-level-2
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