TB Infection Control
Clean Air Delivery Rate – Follow-up on Bacticlean units/UV Lights installation in Botswana discussion
Excellent points made by John in the discussion on Bacticlean units and the installation of UV lights at Princess Marina Hospital TB wards in Botswana: http://www.ghdonline.org/ic/discussion/re-bulk-re-tb-infection-control-infect.... Please allow me to take it one further step.
The clean air delivery rate is dependent on the residence time of the particles in the unit exposed to UVGI (some CFD modelers would call this "age of aerosol") and the minimum UVG irradiance level) not, with proper design, the spread between the extremes of high and low could be minimal. For instance, if we want the CADR to approach the airflow rate, we want the efficiency to inactivate MTB to be 100%. Does it have to be 100%? No but let's say only 50% of the MTB are inactivated. Then the CADR would be 1/2 the airflow rate of the unit and you would need twice as many unit that if the CADR equaled 100% of the airflow rate.
Points to ponder:
1. We must know the CADR for airborne MTB in order to estimate the number of units to provide the equivalent of 6-12 each.
2. We must ensure proper mixing to ensure contaminated air get to the inlet of the unit.
3. No outside air is added to the room; hence, CO2, odors, etc. will build up.
4. Upper-room (unshielded) UVGI system should be considered. I used "system" because this would include proper design, installation, initial testing with appropriate meter, periodic maintenance, periodic UVGI measurement with an appropriate meter, and, of course, education of staff and patients.
Regards,
Paul J
