Safety Devices, Hazards, and Emergency Response
This domain is about the few rules that prevent deaths, so exams phrase them absolutely.
Devices to know
Safety valves and relief valves, low-water fuel cutoff with manual reset, auxiliary low-water cutoff, high steam pressure limit, flame safeguard with scanner, fuel train interlocks and combustion air proving switch, rupture discs, and the fusible plug in fire-tube boilers (melts around 440 to 450 deg F to warn of low water and quench the fire).
Hazards
- Low water is the leading cause of boiler damage and explosion. If the level drops from sight, secure the fuel immediately, do not restore firing, and do not add water until the boiler has cooled and been inspected. Adding water to an overheated, uncovered crown sheet can flash to steam and cause a catastrophic failure.
- Furnace explosion from accumulated fuel ignited late; prevented only by purging before light-off and proving flame on every attempt.
- Overpressure from a blocked, gagged or undersized safety valve.
- Water hammer from slug water, fast valve operation or failed steam traps; open drains and valves slowly.
- Burns, confined spaces, chemical handling, electrical hazards.
Emergency response
On flame failure, low water, high pressure, tube failure, or a fire: cut the fuel first, then the firing controls, isolate the affected boiler from the header, maintain other boilers, notify supervision, and record everything. A lifting safety valve is doing its job - never wedge it or close the isolation.
Traps
Questions offer the seemingly helpful action of adding feedwater to a low-water boiler. That is the wrong answer when the boiler is hot and the level has disappeared.
Worked rule
Order of responses to a low-water condition: cut fuel, kill firing, do not feed, do not open the boiler, then inspect and reset only after cooling and approval.