Editing Steam engine (section)

== Safety ==
Steam engines possess boilers and other components that are [[pressure vessel]]s that contain a great deal of potential energy. Steam escapes and [[boiler explosion]]s (typically [[BLEVE]]s) can and have in the past caused great loss of life. While variations in standards may exist in different countries, stringent legal, testing, training, care with manufacture, operation and certification is applied to ensure safety.{{Citation needed|date=February 2020}}

Failure modes may include:
* over-pressurisation of the boiler
* insufficient water in the boiler causing overheating and vessel failure
* buildup of sediment and scale which cause local hot spots, especially in riverboats using dirty feed water
* pressure vessel failure of the boiler due to inadequate construction or maintenance.
* escape of steam from pipework/boiler causing scalding

Steam engines frequently possess two independent mechanisms for ensuring that the pressure in the boiler does not go too high; one may be adjusted by the user, the second is typically designed as an ultimate fail-safe. Such [[safety valve]]s traditionally used a simple lever to restrain a plug valve in the top of a boiler. One end of the lever carried a weight or spring that restrained the valve against steam pressure. Early valves could be adjusted by engine drivers, leading to many accidents when a driver fastened the valve down to allow greater steam pressure and more power from the engine. The more recent type of safety valve uses an adjustable spring-loaded valve, which is locked such that operators may not tamper with its adjustment unless a seal is illegally broken. This arrangement is considerably safer.{{citation needed|date=January 2013}}

Lead [[fusible plug]]s may be present in the crown of the boiler's firebox. If the water level drops, such that the temperature of the firebox crown increases significantly, the [[lead]] melts and the steam escapes, warning the operators, who may then manually suppress the fire. Except in the smallest of boilers the steam escape has little effect on dampening the fire. The plugs are also too small in area to lower steam pressure significantly, depressurizing the boiler. If they were any larger, the volume of escaping steam would itself endanger the crew.{{citation needed|date=January 2013}}