bonajet;
You are right and I am wrong. The fusible plugs do let steam into the firebox and not into the atmosphere as I thought. It's reasonable to assume that if the plugs were directed into the atmosphere the escaping steam would be seen by the crew but only during daylight. It would not be easily seen at night which is the very time that the original problem of low water in the boiler would go unnoticed. I wonder what the operational procedure was when the crew realised the firebox was filling with steam?? If the fireman opened the firebox door to fuel the fire the cab may have been filled with scalding steam. Perhaps in such a situation they just let the whole engine run down. Any ideas on this?
Prince of Dzun.