5.4 Warning Systems: Master, Area & Local Alarms
Key Takeaways
Every master, area, and local alarm needs separate visual indicators that stay on until the condition is resolved and a cancelable audible signal of at least 80 dBA at 3 ft.
A master alarm system needs at least two panels: one in the work space of the person responsible for the systems and one in a continuously staffed location.
Master and area alarms signal when gas line pressure rises or falls 20% from normal, and when vacuum drops to or below 12 in. HgV.
Medical air dew point alarms activate above +35°F (+2°C) at line pressure, and the carbon monoxide local alarm activates at 10 ppm.
Master alarm and area alarm power comes from the life safety branch, and alarms must restart automatically after a 10-second power loss without false signals.
Features Every Alarm Panel Must Have
All master, area, and local alarm systems must include:
- Separate visual indicators for each monitored condition. Local alarms shown on master panels may be combined, as described below.
- Visual indicators that stay in alarm until the condition is resolved
- A cancelable audible signal of at least 80 dBA at 3 ft (0.92 m) that sounds again if another condition occurs while it is silenced
- Indication of a lamp or LED failure and of an audible failure
- Visual and audible indication that communication with a sensor is lost
- Labeling of each indicator (the condition it monitors) and of each panel (its area of surveillance). The facility must keep room-number labels accurate.
- Power for master alarms, area alarms, sensors, and switches from the life safety branch of the essential electrical system. Local alarms, dew point sensors, and CO sensors may use the same branch that powers the air compressors.
- Wiring supervised or protected as NFPA 70 requires for life safety and critical branch circuits. Non-wired communication must be supervised so a failure triggers an alarm.
- Automatic restart after a 10-second power loss (for example, during generator start) without false signals or a manual reset
- Switches and sensors installed so they are removable and accessible for service and testing
Master Alarms
A master alarm system monitors the source of supply, the reserve source (if any), and the pressure in the main line of each medical gas and vacuum system.
Two locations are required:
- The office or work space of the on-site person responsible for maintaining the medical gas and vacuum systems
- An area of continuous observation, such as the telephone switchboard, the security office, or another continuously staffed location
A centralized computer system may substitute for one of the master panels if it meets NFPA 99's computer-system requirements.
Wiring independence: both mandatory master panels must communicate directly with the alarm sensors. They are wired independently to each sensor, they do not share conductors that could disable more than one signal, and signals are never relayed from one master panel to another. A single sensor may drive multiple master panels. Failure of either panel must not disable any signal on the other.
Master alarm signals
| Signal | Activates when |
|---|---|
| Changeover | A manifold or alternating bulk system changes over, or is about to |
| Low contents (cryogenic main supply) | Main supply reaches one average day's supply |
| Reserve in use | The reserve begins supplying, or is about to |
| Reserve low | Cylinder reserve header or cryogenic reserve contents fall below one average day's supply |
| Reserve pressure low | A cryogenic reserve unit's gas pressure is too low for the system |
| Main line pressure | Line pressure increases or decreases 20% from normal operating pressure |
| Main line vacuum | Medical-surgical vacuum drops to or below 12 in. (300 mm) HgV |
| Local alarm summary | One or more local alarm conditions at a source site |
| Medical air dew point | Line pressure dew point above +35°F (+2°C) |
| WAGD low | WAGD vacuum or flow below effective operating limits |
| Instrument air dew point | Line pressure dew point above -22°F (-30°C) |
| Proportioning system | Primary or reserve production stops |
| Concentrator systems | Concentration from a unit or the system below 91%, unit isolated, header in use or low, unexpected source change, low common-line pressure |
Sensor location: the main line pressure and vacuum sensors go in the main lines immediately downstream (patient side) of the source valves. Where a main line valve is also installed, the sensors go downstream of the main line valve.
Area Alarms
Area alarm panels monitor every medical gas, medical-surgical vacuum, and piped WAGD system supplying:
- Anesthetizing locations where moderate sedation, deep sedation, or general anesthesia is given
- Category 1 spaces
| Rule | Requirement |
|---|---|
| Location | At a nurses' station or a similar location that provides surveillance |
| Gas trigger | Line pressure in the area increases or decreases 20% |
| Vacuum trigger | Vacuum at or below 12 in. (300 mm) HgV |
| Sensors, Category 1 spaces (not anesthetizing) | Patient side of each zone valve box assembly |
| Sensors, anesthetizing locations | Source side or patient side of each room's zone valve box assembly |
| Multiple rooms | One panel may monitor several anesthetizing rooms in the immediate vicinity |
| Mismatch | Panel must indicate a mismatch between a transducer and its circuit board |
Local Alarms
Local alarms monitor the medical air compressors, medical-surgical vacuum pumps, WAGD producers, instrument air systems, and proportioning systems. They may be in the source control panel, in a monitoring device such as a dew point or CO monitor, or on a separate panel. The master alarm must include at least one signal from each source site that activates whenever any required local signal there activates.
Functions monitored at each local alarm site include:
- Low reserve capacity (medical air, vacuum, WAGD, and multi-compressor instrument air): the source is running at a demand it could not meet if one machine stopped
- High carbon monoxide in medical air: 10 ppm or higher
- Medical air dew point high: above +35°F (+2°C)
- Instrument air dew point high: above -22°F (-30°C)
- High water in the receiver (liquid ring or water-cooled compressors) or in the separator (liquid ring)
- High discharge air temperature (compressors other than liquid ring)
- Proportioning system oxygen outside 19.5-23.5%, and reserve in operation
Category 2 and Category 3 Allowances
Category 2 warning systems may be a single alarm panel in an area of continuous surveillance while the facility is operating. Pressure and vacuum switches may be mounted at the source equipment, with a pressure indicator at the master panel. Category 3 may use a single combined master/area panel under the same conditions.
Tip
Two numbers come up constantly: plus or minus 20% for gas line pressure alarms, and 12 in. HgV for vacuum alarms. The air-quality pair is +35°F dew point and 10 ppm CO.
Where must the two mandatory master alarm panels be located?
Both in the medical gas source room
One at each nurses' station on the top two floors
One in the boiler room and one at the main entrance security desk
One in the responsible person's work space and one in a continuously staffed area
At what vacuum level must an area alarm for medical-surgical vacuum activate?
When vacuum drops to or below 12 in. HgV
When vacuum drops to or below 19 in. HgV
When vacuum rises above 25 in. HgV
When vacuum changes by 20% from normal
Medical air dew point is monitored at the compressor plant. Above what line-pressure dew point must the local and master alarms activate?
-22°F (-30°C)
+10°F (-12°C)
+35°F (+2°C)
+50°F (+10°C)
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