Control Room Pressure Relief and Filter Selection for Positive Pressure Spaces

Positive pressure control rooms rely on a steady supply of filtered air to help keep indoor air cleaner than the surrounding plant area. When the room is opened often, that balance becomes harder to maintain, so filter selection, airflow design and maintenance all matter more than ever.

For facility managers, contractors and industrial buyers, the key question is not just which filter fits the housing, but how the whole system performs when doors open, people move through the space and the outside environment changes during the day.

Why filtered air matters in a positive pressure control room

A positive pressure space is designed so air moves out of the room when a door opens, rather than allowing unfiltered air to rush in. That works best when the incoming air is filtered and the system can keep delivering clean air at the required flow.

In practical terms, the filter is part of the pressure control strategy. It helps remove airborne particles from supply air before that air enters the room, so the control room can stay cleaner than adjacent areas such as workshops, process spaces or loading zones.

That does not mean one filter type suits every site. The right choice depends on:

• •the level of airborne dust or contamination around the building
• •how often the door is opened
• •whether the room is occupied continuously or intermittently
• •the fan or air handling setup already in place
• •the filter resistance the system can handle without losing airflow

If your project also involves other plant or building spaces, it can help to review our products alongside the room’s design requirements.

What happens when the room is frequently opened

A control room that opens only now and then is easier to keep stable than one with regular movement in and out. Frequent door opening creates a pressure leak path, and every opening gives outside air a chance to enter before the pressure is re-established.

That means the filtration system has to work harder to support the room’s pressure balance. If the incoming filters are too restrictive, too coarse, or left in place for too long without inspection, the system may struggle to deliver enough air volume.

Common pressure challenges in frequently opened spaces

• •Door opening breaks the pressure barrier repeatedly
• •Dust from nearby plant areas can be pulled into the room during each opening
• •A clogged filter can reduce supply airflow and weaken pressure control
• •Poor sealing around doors, panels or cable penetrations can undo good filtration
• •Changes in occupancy or equipment load can affect the pressure balance

For rooms that are opened often, pressure relief and filtration should be considered together. The aim is to allow the system to recover quickly after each opening without oversizing the fan or creating unnecessary noise or draughts.

Choosing the right filter for the job

Filter selection should start with the contaminant load in the surrounding environment. A control room near a dusty production area needs a different approach from one located in a relatively clean administrative zone.

Factors to weigh up

• •Particle size and dust load: Heavier dust conditions usually call for more effective pre-filtration or staged filtration.
• •System resistance: Higher-efficiency filters generally create more resistance, so the fan and housing must be suitable.
• •Access for maintenance: If the filters are difficult to reach, practical servicing matters just as much as nominal efficiency.
• •Housing fit: The filter needs to suit the frame, seal properly, and avoid bypass around the edges.
• •Operating environment: Heat, humidity, vibration and nearby process emissions can all influence filter performance.

In many control room applications, a staged approach works well: a coarse pre-filter to catch larger dust, followed by a finer final filter where the system requires it. The exact arrangement should be matched to the equipment and site conditions.

If the control room is part of a larger facility project, commercial filter servicing may also be worth considering during planning.

Standards, ratings and the role of the engineer

Air filtration in commercial and industrial buildings is often discussed alongside ventilation requirements under AS 1668.2:2024. That standard is relevant to how buildings are ventilated, but site requirements still need to be confirmed with the mechanical services engineer or building owner.

When comparing filters, avoid assuming that one rating system converts neatly into another. MERV, EN 779 and ISO 16890 are not direct equivalents, so it is better to compare the actual product data and the needs of the system rather than relying on rough conversions.

You may still see G3/G4 and F5-F9 used in Australian projects. These are EN 779 classes, and although that standard has been superseded by ISO 16890, the older terminology is still widely used in the field.

For applications where very fine particle capture is required, HEPA filters may be specified. Under EN 1822, H13 filters are rated at at least 99.95% efficiency at the most penetrating particle size, and H14 filters at least 99.995% at MPPS. Whether that level is appropriate depends on the room design and the broader air handling strategy.

Maintenance matters when pressure has to stay stable

A positive pressure room can only perform properly if the filters are maintained in line with the system’s needs. As dust builds up, resistance rises and airflow can fall, which affects pressure control.

The best approach is to inspect the filters based on the system, site conditions and dust load, and to follow the filter or equipment manufacturer instructions. Where gauges are fitted, monitor pressure drop so you can see when a filter is becoming loaded.

Good maintenance practice includes

• •checking seals, frames and filter seating during service visits
• •looking for signs of bypass, damage or dust tracking around the housing
• •confirming that fan performance still suits the required airflow
• •recording pressure readings where gauges or monitors are installed
• •replacing or servicing filters according to the actual condition of the system, not a fixed calendar alone

Some filters are designed to be washable - check the product instructions before cleaning or reusing any product. Others are intended for replacement only.

If your site needs ongoing support, filter servicing can help keep the system in better working order.

When custom filters make sense

Standard sizes are often suitable, but not every control room uses standard housings or off-the-shelf dimensions. Older buildings, retrofit projects and plantroom-adjacent control spaces may need filters made to size so the housing seals properly and the system performs as intended.

Custom filters can be useful when:

• •the existing frame size is unusual
• •the room upgrade is being done around legacy equipment
• •sealing and fit are critical to pressure control
• •access is tight and the available product range is limited
• •the project needs a specific media type or frame construction

If you are measuring an existing unit for replacement, use the correct method so the new filter matches the housing properly. Our guide on how to measure an air filter can help with that step.

Supplying the right filter for positive pressure spaces

The right filter selection depends on the room, the dust load and how often the space is opened. Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, and we can supply or make filters to suit a wide range of control room applications.

If you are planning a new install, a retrofit or a servicing visit, call 07 3800 3448 or request a quote. For site-specific help, you can also contact us or view the industries we supply.