Pressure explosions occur when a pressure part of the boiler such as the shell, furnace, or firetube bursts due to too high a steam pressure or a structural weakening of the metal. This weakening may be caused by:
1. corrosion
2. thermal stress
3. overheating
4. scale and sludge build-up
5. insufficient combustion air
a) 1, 3, 4, 5
b) 2, 3, 4, 5
c) 1, 2, 3, 4
d) 1, 2, 4, 5
e) 1, 2, 3, 5
Answer: A