Gas Boiler Emergency Shutdown Guide | 5 Critical Conditions for Immediate Shutdown

1. Combustion System Runaway

Gas Leakage Alarm

• Gas detector reading exceeds 20% LEL → immediate shutdown required.

• Close the main gas valve instantly.

• Do NOT start exhaust fans to avoid igniting leaked gas.

Flame Failure

• If the burner flame disappears and the gas supply is not shut off within 2 seconds, explosive fuel-air mixtures may form inside the furnace.

Deflagration / Flashback

• Furnace pressure spike exceeds 500 Pa.

• If the explosion-proof door fails to open, perform manual emergency shutdown immediately.

2. Pressure-Boundary Failure Warning Signs

Water Level Out of Control

• Extremely low water level (water disappears from sight glass).

• Full water condition causing steam-water carryover and water hammer risks.

Pressure Surge

• Working pressure exceeds the safety valve lift pressure but the valve does not open.

• Example: design pressure 1.0 MPa → actual pressure spikes to 1.2 MPa.

Pressure Components Failure

• Tubes, drum shell, or weld joints leak, deform, or crack.

• Shut off all fuel and begin depressurization immediately.

3. Failure of Critical Safety Devices

Dual Water Level Gauges Fail

• Both level indicators unreadable → operating blindfolded.

Pressure Gauge Malfunction

• Pointer stuck or unresponsive → shutdown is safer than operating with unknown pressure.

Safety Valve Failure

• No venting during manual lift test → immediate shutdown required.

4. Power and Pump System Failure

Feedwater Pump Failure

• If all feedwater pumps stop and cannot resume within 30 seconds → emergency shutdown to prevent dry-firing.

Circulation Pump Failure (Hot Water Boilers)

• Pump failure leads to water stagnation and rapid vaporization, causing pressure spikes above 0.1 MPa.

• Atmospheric boilers must never operate under pressure.

5. Environmental Threats Requiring Immediate Shutdown

Earthquakes / Strong Impacts

• Vibration may cause gas line displacement or leakage.

• Shutdown must be completed within 30 seconds.

Sudden Power Outage

• Close the main gas valve.

• Manually open the emergency pressure release valve.

Emergency Shutdown Procedure

The Golden Three Steps

1. Cut off the gas supply

2. Release pressure safely

3. Force ventilation (Do NOT open the furnace door immediately)

Forbidden Actions

• No blowdown within 10 minutes after shutdown (prevents thermal shock and cracking).

Post-Shutdown Mandatory Inspections

• Identify the root cause before restart.

• A pressure test is required before ignition.