Preparing a Room for VHP Decontamination: Sealing, HVAC Isolation and Placement

Free download: Room VHP decontamination checklist (PDF)

The checks in this guide as a printable two-page form, with an indicator log and sign-off. Get it →

1. Define the boundary

Before anything else, decide exactly what is being decontaminated. One room, or a suite? Does the air handling ductwork need treatment as well, or only the room surfaces? Which adjoining spaces will stay occupied?

The answer determines the equipment. A mobile generator treats the room with the HVAC isolated. If the ducts are part of the contamination concern, or several rooms must be treated together, an HVAC-integrated system that distributes vapour through the air handling plant is usually the better fit.

Record the boundary on a drawing, with the room volumes. Volume, together with the materials inside, is the starting point for dose and cycle design.

2. Survey what is in the room

• Remove paper, cardboard, cotton, wood and liquids — they absorb vapour and lengthen aeration. See the material compatibility guide.
• Open cabinet doors, drawers, equipment covers and biosafety cabinet sashes that should be treated.
• Separate and raise items so that surfaces are not stacked or resting flat on benches and floors.
• Clean first. VHP is not a cleaning agent. Visible soil, residues and films shield microorganisms from the vapour.
• Note heat sources and cold surfaces — fridges, incubators, external walls, chilled pipes. Cold surfaces are where condensation forms first.

3. Seal the room

A room has to hold concentration for the whole exposure phase. Leaks lower the dose at the walls and doors — often exactly where the hardest locations are — and expose people in adjacent areas.

• Doors: check gaskets; tape the perimeter of doors that are not airtight. Airtight doors with inflatable or mechanical seals remove the need for taping.
• Penetrations: cable trays, pipe entries, sockets, ceiling light fittings, sprinkler heads and access hatches.
• Drains and sinks: fill traps or cap the outlets.
• Pass-throughs: close both doors and include the pass box in the boundary or seal it off.
• HVAC: with a mobile generator, close supply and return dampers or seal the grilles, so vapour is neither exhausted nor carried into other zones. Plan how the HVAC will be restored for aeration.

Decide whether the room is held at neutral pressure or slightly negative to its surroundings during the cycle, and make the decision part of the procedure. Outward leakage is a safety issue, not only an efficacy issue.

4. Place the generator and fans

• Put a mobile generator where its output can mix with the whole room, usually near the centre, and never aimed directly at a nearby surface — a concentrated jet on a cold surface is a condensation point.
• Use mixing fans to move vapour into corners, behind equipment and into alcoves. Fan positions are part of the cycle and should be fixed in the procedure once validated.
• Keep the generator’s own sensors and cables clear of doors and seals.

5. Sensors and indicators

Hydrogen peroxide concentration, relative humidity and temperature should be monitored at representative points, including at least one location expected to be worst case. Biological indicators (BIs) and chemical indicators (CIs) go where the vapour is least likely to reach the required dose:

• Corners at floor and ceiling level, and the corners furthest from the generator.
• Behind and underneath fixed equipment, inside cabinets and equipment housings.
• Near the door and near any sealed opening where leakage would dilute the vapour.
• Next to absorbent materials that could not be removed, and on cold surfaces.

The number and positions come from the mapping study for the room. Once validated, the same positions are used for routine monitoring and periodic requalification, so record them on the room drawing.

6. Safety before, during and after

• Post warning signs on every entrance and control access to the room and the plant room serving it.
• Monitor adjacent areas and door seals for leakage during exposure, using a low-range detector.
• Define who can stop the cycle and how, and what happens if a leak is detected.
• Release the room only after a documented reading at or below the limit — see aeration and residual limits.

Checklist