How to fix airflow in prisons
TB is an airborne disease with an increased potential for transmission in poorly ventilated and overcrowded spaces. An infectious individual is far more likely to transmit TB in such environments. Unfortunately, conditions in South African jails have meant that prisons are particularly undesirable settings for the control of the disease.
How safe a prison environment is for prisoners and staff depends on the conditioning and control of the air coming in and going out, and how this flow is managed.
The principles are simple: purge the air from the space occupied by a TB patient and discharge all of it so that no part is recirculated. Also make sure that the number of air changes in an hour are such that the level of CO2 in the air inside is no higher than the level of CO2 in the air outside. Spaces must be configured to function in all expected local weather conditions.
Experience has shown that unless a mechanical system maintains the number of air changes, it is almost impossible to keep a constant, measured flow of air and ensure a sufficient purging of the space. Natural ventilation alone is too unreliable and does not ensure the required number of air changes.
Natural ventilation depends on air movements. These stop once the interior and exterior temperatures equalise, unless there is a constant, natural minimum wind speed outside – and this is highly improbable.
Just installing fans are not good enough since it does little to prevent cross contamination.
How prisons should be designed
1. The air entering the patient’s room should be fresh and contain no part that has been recirculated
2. An anteroom adjacent to the patient’s room should act as both an airlock and a positively pressured chamber. In other words, the air in the anteroom should be maintained at a constantly higher level of pressure than the air in the patient’s room
3. Air is then drawn from this airlock into the patient room’s room which is negatively pressurised (i.e. the air pressure in the patient’s room). This imbalance in air pressure prevents any air containing live bacteria from migrating back into the building and into other adjacent rooms
4. The air from the patient’s room is discharged into a duct and exposed to an appropriate frequency of ultraviolet light for a brief prescribed period. This exposure kills nearly 90% of the TB bacteria in the air. The purged air then needs to be discharged from the building as far away as possible from the fresh air that is brought into the air system so that cross contamination is avoided.
This configuration has been used successfully for many years and has achieved the kind of infection control which other strategies have consistently failed to achieve.Based on notes shared by the architect Paul Silver FAIA NCARB