OT HVAC Maintenance: Air Changes, HEPA, Pressure

An operation theatre can look spotless and still fail a patient. If the AHU is pushing air through a HEPA filter with a torn gasket, or the room has quietly drifted from positive to neutral pressure because someone keeps wedging the scrub-room door open, every wipe and fogging cycle is working against an invisible leak. Operation theatre HVAC maintenance is infection control carried out with gauges and spanners, and in many hospitals it still lives in a logbook that only the HVAC contractor ever reads.

Why OT HVAC matters for infection control

The ventilation system in an OT does several jobs at once. It dilutes airborne particles and microorganisms shed by the surgical team through frequent air changes. It delivers filtered air downward over the operating table, usually through a unidirectional or laminar flow ceiling, so contaminants are pushed away from the wound. It keeps the theatre at a higher pressure than the corridors around it, so air leaks outward rather than in. And it holds temperature and humidity in a band that keeps staff comfortable and prevents condensation and microbial growth on surfaces.

The NABH standards expect hospitals to monitor and maintain the OT environment under both the infection prevention and control (IPC) and facility management (FMS) chapters, and ASHRAE design guidance for healthcare ventilation is widely used by Indian HVAC consultants. Exact values for air changes, pressure differentials and temperature bands should come from your design basis and your infection control committee. The job of maintenance is to keep the system performing to that basis every single day, and to prove it. Our NABH FMS playbook covers the wider documentation picture.

The core parameters to monitor

How do you maintain HEPA filters in an OT?

Terminal HEPA filters are the last line of defence, and the pre-filters and fine filters upstream exist to protect them. In practice, most HEPA problems are not media failures. They are gasket leaks, frames damaged during installation, or air bypassing the filter around a poorly sealed housing.

• Change pre-filters when their pressure drop reaches the set limit, not only on a calendar date. A choked pre-filter starves the fan and lowers air changes long before anyone feels it.
• Never wash, vacuum or blow out a HEPA filter. When its pressure drop reaches the manufacturer's replacement point, replace it.
• Book the integrity test together with the replacement. A new HEPA that has not been leak-scanned is an assumption, not a control.
• Store the test certificate, filter serial number and installation date against that OT's asset record.
• Look for dust streaks on the diffuser face or ceiling around the housing, which often signal bypass leakage.

Keeping the pressure cascade intact

An OT complex is designed as a cascade, with the theatre at the highest pressure, followed by the scrub area and sterile store, then the clean corridor, and finally the dirty or return corridor at the lowest. The cascade breaks for mundane reasons far more often than for dramatic ones.

• Door closers that weaken, or doors propped open for trolley movement.
• False-ceiling tiles lifted for cabling or lighting work and never put back.
• Return-air grilles blocked by stacked equipment or linen trolleys.
• A slipping fan belt or a VFD setpoint changed during an energy-saving drive.
• Dampers adjusted by someone chasing a temperature complaint without checking pressure.

Make the pressure reading part of the pre-list routine, owned by the OT technician or nurse, with a photo of the gauge. A wrong reading goes straight to engineering, and the decision on whether the list proceeds sits with the OT in-charge and infection control, not with engineering alone.

A practical OT HVAC maintenance schedule

Daily

• Room pressure, temperature and humidity recorded before the first case and at defined intervals.
• AHU running status, fan current and any BMS alarms reviewed by the shift engineer.
• Visual check of diffusers, return grilles and door closers.

Weekly and monthly

• Filter pressure drops recorded and pre-filters changed at the trigger point.
• Belts, bearings, drain pans and condensate lines inspected; coils checked for fouling.
• Humidifier or dehumidifier performance verified, especially before the monsoon.

Quarterly and annual

• Air-change measurement and pressure balancing across the OT complex.
• HEPA integrity testing and particle counts as per the validation schedule.
• Full AHU service, coil cleaning, duct inspection and sensor calibration.

The AHU maintenance checklist breaks these tasks into checkable items your team can run on every OT unit.

Coordinating engineering and housekeeping

Consider an illustrative scenario at a hospital in Chennai. Housekeeping completes a weekend terminal clean of OT 2 on Saturday afternoon. On Saturday evening, the HVAC vendor changes the pre-filters and opens a ceiling panel to inspect the HEPA housing. Nobody tells housekeeping. On Monday morning the first case starts in a theatre with fresh dust on the pendant arms and lights. Each team did its job; the sequence failed.

The fix is a single linked workflow: engineering work first, then a terminal clean using the OT cleaning checklist, then a pressure check and, where the change requires it, a particle count, then a signed release by the OT in-charge. The principles behind that clean are covered in terminal cleaning vs daily cleaning.

Records that stand up to an audit

Assessors and infection control committees want evidence that the OT environment is monitored and that deviations are acted on. That means daily logs, filter change records, HEPA test certificates, validation reports and closed deviation tickets. Paper sheets at the OT door often show identical readings day after day, which tells an assessor more about the logbook than the air. Time-stamped entries with a gauge photo are far harder to doubt.

humblx Facility Maintenance schedules OT HVAC preventive tasks, captures readings with photo proof and turns any out-of-range value into a tracked work order, while Housekeeping records the terminal clean that follows.

Your OT HVAC action list

1. Pull the latest OT validation report and confirm everyone knows the acceptance values for each theatre.
2. Put a photographed pressure reading into every pre-list routine.
3. Switch pre-filter changes to a pressure-drop trigger.
4. Check that every HEPA has a current integrity certificate on file.
5. Link HVAC work orders to a mandatory terminal clean and signed OT release.