Negative Pressure in a Hospital Mechanical Room
A crew is removing 200 linear feet of friable thermal-system insulation from a hospital mechanical room measuring 40 feet by 30 feet by 10 feet. The room has one 3-foot-by-7-foot door, no windows, and an operating suite on the adjacent wall. The crew builds containment with 6-mil polyethylene, seals seams with duct tape, and installs one HEPA negative-air machine rated at 2,000 cubic feet per minute. The door is covered with overlapping plastic flaps. A portable shower is not available; workers plan to change and wash in a locker room down the hall. The supervisor measures negative pressure at one location and reads 0.02 inches of water gauge, but a smoke test shows leakage at the door flap and at a pipe penetration. The hospital’s infection-control staff want continuous negative pressure relative to the operating suite and a written emergency plan. The work is scheduled over a weekend, and the operating suite will remain in use.
1. Calculate the air changes per hour and evaluate whether the negative-air machine is adequate. What factors reduce actual performance?
Read the worked answer
The room volume is 40 × 30 × 10 = 12,000 cubic feet. A 2,000-cfm machine moves 2,000 × 60 = 120,000 cubic feet per hour, which is 10 air changes per hour at free-air rating. That is generally adequate for a small containment, but the rating is not the same as installed performance. Filter loading, long or crushed duct, inadequate makeup air, and leakage at the door all reduce actual flow. The crew should verify flow at the machine and at the exhaust, not rely on the nameplate. A single pressure reading is also insufficient; the pressure should be monitored continuously or at frequent intervals, with an alarm or backup power, and the smoke test shows that the containment is not tight. The door flap and pipe penetration must be resealed before work continues, and a second negative-air unit should be available in case the primary unit fails.
2. Identify the containment and decontamination deficiencies and the corrections needed.
Read the worked answer
Duct tape alone is unreliable on polyethylene, especially over time or under negative pressure; seams should use spray adhesive, furring strips, or overlapping folds, and penetrations should be sealed with compatible sealant and a rigid collar. The door should have a double-flap or zipper entry that maintains negative pressure, not loose overlapping plastic that leaks. For Class I removal, a decontamination unit with a shower is required before employees leave the regulated area; a locker room down the hall is not a decontamination unit. The crew needs a clean room, shower, and equipment room, or a written alternate only where the standard permits it. Waste should be bagged in the containment, HEPA-vacuumed, and removed through the decon sequence. The supervisor should also verify critical barriers over supply and return grilles and seal all openings that could communicate with the operating suite.
3. What hospital-specific coordination and monitoring should be done before and during the weekend work?
Read the worked answer
The contractor should complete an infection-control risk assessment with the hospital and coordinate with the operating-suite manager. The HVAC serving the mechanical room should be isolated, and the containment should be maintained under negative pressure relative to occupied spaces, with smoke testing and continuous pressure monitoring. The hospital should confirm that return-air pathways do not connect the work area to the operating suite. An emergency plan should address power failure, negative-air failure, fire alarm, and medical emergency, with a designated contact and evacuation route. The contractor should monitor pressure and filter condition, keep a log, and stop work if pressure is lost. Air sampling may be used for verification, but it does not replace engineering controls. The weekend schedule should include time for clearance and for the hospital’s infection-control approval before the suite resumes normal operation.