Which of the following is a common boiler safety device?

A safety valve is a critical component in boiler systems designed to prevent excessive pressure from building up within the boiler. When the pressure inside the boiler exceeds a predetermined limit, the safety valve automatically opens to release steam or water, thus preventing potential catastrophic failures such as explosions. This mechanism is essential for maintaining safe operating conditions, ensuring that the pressure remains within acceptable levels.

Other devices mentioned, while useful in their own right, do not primarily serve the same safety function. An electric igniter is used to initiate combustion in the boiler, but it does not provide safety against pressure issues. A pressure relief door, depending on the context, may not be a standard term or component related specifically to boiler safety, potentially leading to confusion in its function. Similarly, a steam gauge is crucial for monitoring pressure within the boiler system but does not actively intervene to mitigate risks like the safety valve does. Thus, the safety valve stands out as the primary safety device commonly employed to safeguard against the dangers of excessive pressure in boiler operations.