This is an area where an industrial hygienist with strong skills in ventilation requirements analysis could be very useful to compounding pharmacies in terms of energy savings and protection from airborne hazards over the long term. In that spirit, we offer the following discussion.
A room contains a volume of air; replacement of all the air in a room with ‘new’ air – also called replacement air — is one air exchange.
But an air exchange doesn’t happen all at once, so the math for applying an air exchange rate to the design of a ventilation system can be tricky.
So recommended air exchanges are generally expressed as a range, not a specific number.
It makes sense that air exchanges can help determine the comfort level and acceptable air quality in a room.
Dilution ventilation and local ventilation
Air exchanges are a form of dilution ventilation, in which new, cleaner air is blown into a room while dirtier air is exhausted out of the room.
Lab hoods are a form of local ventilation, in which contaminants are pulled away from workers’ breathing zones as close to the contaminants’ source as possible.
Both types of ventilation, dilution and local, are used in industrial and laboratory situations.
A Washington State Dept. of Labor & Industries website published the useful chart below to compare the two types of ventilation.
Compounding pharmacies are not identical
Variety among compounding pharmacies includes number of employees, size of building, number of rooms, ceiling heights — all can greatly influence ventilation requirements.
Compounding pharmacies need both local and dilution ventilation, but both should be right-sized for the tasks people perform in the pharmacy.
Air exchange “standards”
It appears there are no mandatory air exchange rates for labs or compounding pharmacies other than suggested ranges for comfort.
You can come across reference OSHA non-mandated ‘recommendation’ of 8-12 air exchanges per hour for laboratories on many websites. However, it is difficult to trace the source of that recommendation.
In their much used, often cited industrial ventilation manual, the American Conference of Governmental Industrial Hygienists says,
“Air changes per hour” or “air changes per minute” is a poor basis for ventilation criteria where environmental control of hazards, heat, and/or odors is required.
“The required ventilation depends on the problem, not on the size of the room in which it occurs.”
A numerically specific air exchange rate is difficult to engineer into a ventilation system.
When compared to local ventilation, dilution ventilation (air exchanges) is not the most effective method for removing highly toxic airborne hazards from workplace air.
High air exchange rates produce high energy costs.
Are there additional ways to approach the ventilation of compounding pharmacies?
Given the lack of mandatory requirements, and the opinion of experts like industrial hygienists, what should the USP recommend?
Does specification of a specific number of air exchanges per room provide adequate or improved employee safety?
Should the USP provide a list of criteria that determine air quality and airborne hazards in each pharmacy? (In addition to air pressure and air exchanges, such criteria might include airborne particle counts.)
If a criteria list existed, would pharmacists have access to the tools they need to meet it?
We think compounding pharmacists may want to talk about the air-exchange issue.
Give us a call
Industrial Ventilation, a Manual of Recommended Practice, American Conference of Governmental Industrial Hygienists
Chapter16. Laboratories, ASHRAE handbook on laboratories
University of North Carolina UNC Laboratory Design Guidelines