Hospital doors with differential pressure control are sealed systems that regulate airflow and access between critical areas (such as operating rooms, ICUs or cleanrooms) and corridors. In areas such as isolation ICUs, operating rooms or sterile pharmacies, each door opening alters the pressure gradient between rooms, and the solenoid that keeps it closed is one of the most important components for ensuring correct operation.
What is differential pressure control in hospital access systems?
Differential pressure control consists of maintaining a deliberate difference in air pressure between two adjacent spaces, so that air always flows in a specific direction. This difference prevents air (and with it, particles or biological agents) from passing from one area to another in an uncontrolled manner.
Negative pressure for infectious patient isolation
In respiratory isolation rooms or ICUs for infectious patients, the room is maintained at a lower pressure than the corridor. This means that air flows into the room when the door is opened, rather than the other way around, preventing pathogens from escaping into the rest of the ward.
Positive pressure for operating rooms and sterile areas
In operating rooms, sterile preparation rooms or hospital pharmacies, the objective is the opposite: the room is maintained at a higher pressure than its surroundings, so that air flows outward when the door is opened, preventing contaminants from entering from less-clean areas.
Why is the door the critical point in the pressure gradient?
The HVAC system may be perfectly sized, but the door is the element that introduces the greatest pressure losses during each opening cycle. Slow closing, a poorly compressed seal or a solenoid with insufficient holding force can compromise the pressure gradient designed by the HVAC engineer, regardless of how well the rest of the system has been calculated.
The role of the solenoid in a pressure-controlled door
In a hospital door with differential pressure, the solenoid does more than simply lock the access: it forms part of the system that ensures the room immediately recovers its design pressure after each opening.
Holding force and airtightness under differential pressure
The solenoid’s holding force must be sufficient to compress the door’s perimeter seal against the frame, even when there is an active pressure difference pushing the door leaf in the opposite direction. An undersized device allows air micro-leaks that continuously degrade the pressure gradient, even though the door appears to be closed.
Fail-safe versus fail-secure depending on the type of isolation
- Fail-safe: releases the door when electrical power is lost. This is mandatory on evacuation routes and in most hospital access points under fire safety regulations.
- Fail-secure: maintains the lock without power. It is reserved for access points where preventing the uncontrolled release of a biological agent is the priority, provided that the facility’s evacuation regulations allow it.
The choice between the two depends on the project’s risk assessment: in most hospitals, safe evacuation takes precedence, but in high-level biocontainment areas, the design may require specific solutions coordinated with the facility’s safety team.
Applications by type of hospital area
ICUs and infectious patient isolation rooms
Negative-pressure rooms where the solenoid must ensure a consistently airtight closure, as any leakage directly compromises infection control within the ward.
Operating rooms and sterile areas
Positive-pressure rooms with frequent opening cycles during personnel or material changes. The solenoid must combine holding force with a rapid response to minimise the time the door remains open. When the operating room also requires airtightness against other environmental factors, it is advisable to review solutions for airtight and special-purpose doors.
Pressure airlocks between areas with different pressure levels
Intermediate spaces where two doors must never be open at the same time. The solenoid is integrated into the system’s interlocking logic to ensure that a barrier always remains closed between the two areas.
Hospital pharmacies and sterile preparation areas
Medication-handling areas where pressure control prevents cross-contamination of products, with high duty-cycle requirements due to the constant movement of personnel.
Benefits of a properly sized locking system
A solenoid correctly specified for this type of installation provides:
- Maintenance of the pressure gradient designed by the HVAC project, cycle after cycle.
- Integration with the BMS of the hospital, allowing the status of each door to be monitored in real time.
- Reduced maintenance compared with mechanical systems, as there are no moving parts subject to wear.
- Custom manufacturing when the required force, operating voltage or protection rating do not match a catalogue model.
At NAFSA, we design and manufacture electromagnets for door locking systems adapted to demanding environments, including hospital facilities with differential pressure requirements. We also provide solutions for access control and custom manufacturing when required by the project. If you are working on a hospital installation with controlled pressure requirements, you can contact our team to discuss your project’s technical specifications.
Frequently asked questions about solenoids in hospital doors
What is the difference between positive and negative pressure in hospital access systems?
Positive pressure keeps the room at a higher pressure than its surroundings, so that air flows out when the door is opened and prevents contaminants from entering; it is used in operating rooms and sterile areas. Negative pressure does the opposite: the room is maintained at a lower pressure so that air flows in rather than out, preventing the spread of infectious agents; it is used for patient isolation.
What type of solenoid is used in a pressure airlock?
It depends on the type of safety required by the project, but electromagnetic holding magnets or linear solenoids are typically used, integrated into the interlocking logic of the control system, which prevents both airlock doors from remaining open simultaneously.
What IP rating does a solenoid need in a hospital area that is frequently cleaned?
In areas subject to intensive disinfection protocols, an IP65 rating or higher is recommended to ensure resistance to water jets and cleaning products without compromising the device’s operation.