• The levels of protection afforded workers must be reliable, consistent, and adequate.
• The efficacy of the protection for each individual worker must be determinable during use throughout the life span of the system.
• The solution must minimize dependence on human intervention for its efficacy so as to increase its reliability.
• The solution must consider all routes of entry into worker's bodies and should not exacerbate existing health or safety problems or create additional problems of its own.
The fundamental strength of the control hierarchy is that it minimizes the likelihood that prevention will "break down" to the extent that results in a hazardous exposure to workers. The control hierarchy for a recognized hazardous source proceeds as follows:
1. Under ordinary circumstances, the most effective and reliable control method is substitution of a less hazardous substance or source of exposure for the more hazardous one. Obviously, when the source of a hazardous exposure is a person with infectious tuberculosis, "substitution" as a potential control method is not possible.
2. The next most effective approach is to prevent or contain hazardous emissions at their source. In the health-care setting, this is best implemented through administrative controls (e.g., rapid identification, early treatment, and isolation of potential tuberculosis transmitters; limiting worker access to acid-fast bacilli (AFB) isolation rooms; other isolation precautions). Other administrative controls might include providing necessary services and procedures (e.g., portable X-ray units) in the room of a confirmed or potential tuberculosis transmitter rather than moving the infectious person to the service. Additionally, engineering controls should be used (e.g., negative-pressure ventilation for AFB isolation rooms to contain any airborne hazard to these rooms; booths, hoods, tents, or other devices for containing droplet nuclei at the source–i.e., a person with infectious pulmonary tuberculosis).
