This post continues our blog's examination of the exciting world of dust, why dust can be dangerous and the 'art' of containment. Again, the goal of this blog is to provide the very basics, the foundation, of infection and dust control.
I have written over the past two months about:
1. How dust becomes infected and what is in dust.
2. Dust containment and the HEPA-filtration standard as to the prevention of hospital acquired infections.
3. The relationship air-flow and air-pressure have to filtration and containment.
There is another important component to air-flow, air-pressure, filtration and containment related to infection control practices that we have not discussed. The actual calculation of air-flow often as a cited criteria for effective containment is known as Air changes per hour or ACH. ACH is simply the measure of air volume that can be added/removed from a space in a given hour. One air change results when all air has been replaced. It is a complete recycling of the air.
It might seem complex but the calculation is simply: Air Changes Per Hour = Volume of Air Flow in cubic ft. per minute (60) / Cubic feet of the area. In practical terms, a negative air machine with a cfm of 500 (pulling 500 cubic ft. per minute) pulling from a 2,000 cubic foot area is 500 cubic feet x 60 minutes / 2000 cubic feet = 15 Air Changes Per Hour or ACH.
General guidelines are that spaces with immunocompromised patients have 15 ACH or more. If there are not immunocompromised patients then many facilities accept 12 ACH. Operating and delivery rooms usually have recirculating air systems that provide 25 ACH.