Can the BMS be the only medical gas alarm?

No. HTM 02-01 (2026) says the BMS should not be used in place of the plant alarm system, and the NFPA 99 2021 edition only let a supervised computer system replace one of the two required master alarm panels.

Why are alarm relays closed when there is no fault?

So that a power failure opens the contact and shows as a fault, just like a gas or system fault. HTM 02-01 (2026) describes this as a fail-safe design that also simplifies BMS integration.

How do medical gas alarms connect to a BMS?

Q: How are medical gas alarms connected to the hospital BMS: Modbus, BACnet or potential-free contacts?

Under NHS England's HTM 02-01 (2026), medical gas alarms connect to a hospital building management system (BMS) through volt-free relay contacts for monitoring only: the stand-alone medical gas alarm system stays in place and the BMS should not control the plant.

How are medical gas alarms connected to the hospital BMS: Modbus, BACnet or potential-free contacts?

The rule in HTM 02-01: monitor, not replace

HTM 02-01 (2026 edition) says medical gas alarms should be a stand-alone alarm system that may be mirrored to other devices for monitoring only. Plant alarms should be connected to the BMS for monitoring purposes only, and the BMS should not be used in place of the plant alarm system. Area alarms should be capable of being monitored by the BMS, with output provided for outward reporting only. For manifolds and compressor plant, the guidance adds that the BMS should only monitor and should not control plant functions, changes or isolations. Links to nurse call or general alarm management systems are an extra layer, not a replacement for the primary medical gas alarm system.

Portugal's ACSS specification ET 03/2006 (2024 revision) asks that the alarm systems of each department's pressure regulators, and the vacuum alarms of each department, allow connection to the building automation and control system (SACE).

Potential-free contacts

The interface HTM 02-01 describes is the volt-free relay contact. It asks for alarm relays that are energised in the closed condition (closed means no fault, open means fault) and drop open on loss of power. A gas fault, a system fault or a power failure then all reach the BMS as the same open contact, which keeps the interface fail-safe. In plant alarm systems, transmitters convert the volt-free contacts of the plant or manifold into a multiplexed signal with line monitoring, and multi-core alarm cables should serve the medical gas alarms only.

Modbus, BACnet and other data links

HTM 02-01 does not name a data protocol such as Modbus or BACnet. In the US, the 2021 edition of NFPA 99 let a computer system replace one of the two required master alarm panels only under conditions: continuous operation, supervision of interface devices such as electronic interfaces or 4 to 20 mA cards so that their failure raises an alarm, supervised communication with the sensors, and the priority of a life safety signal for medical gas alarms; NFPA now lists the 2027 edition as current. HTM 02-01 also asks for a system fault indication if data transmission between panels and transmitters is lost.

On Ultra Controlo equipment

On ULTRAOX plants, all alarms are on an interface for remote signalling, and the control panel is designed to receive alarm cables without drilling (ULTRAOX datasheet 2022, p. 16). The ULTRAOX SC and ULTRAOX ST datasheets (p. 4) list a complementary information control box for building management systems. ULTRAAR SCA medical air plants bring out all alarms on an interface for remote signalling, and ULTRASEG offers supplementary information for a BMS as an option. The ACIH industrial compressed air system, which is not a medical gas, has an RS 485 Modbus RTU interface.