stick thier fingers in thier ears? Accept the long term hearing loss?
AFAIK that was also the case back when steam was mainstream power (and because blowing off steam wastes fuel - money - and firing effort).
As regards the noise, and how crews cope with it, unless a spring had weakened, the valve would not normally lift for long, so most crews accepted it as part of the job, some are louder than others, depending where on the boiler the safety valves are, On an A4 they're closer to the cab, and as a result quite loud.
The "Pop" safety valves are the most extreme in my experience, other types give you a bit of warning that they are lifting, but pop valves just explode at full pressure. I think they are designed to do that so that they a) don't waste steam by lifting early and b) shut suddenly and firmly when the pressure has dropped a bit.
I suspect the link between railway enthusiasm and autism and common methods of mitigating the effect loud or sudden noise can have on such people in the modern era is the answer.In the last few years there has been a noticeable increase in the number of children and young adults to be seen at heritage railway with ear defenders! Now I recall my first experience of a safty valve lifting at Lime Street Station around 1963/4. My grandmother has been away in Africa visiting my aunt for three months the day she was returning home my mother took me down to to meet her coming off the Euston train in pre electrificatin days and this grimy loco possibly a Black 5 lifted its safety valves. I didn't like it the first time but then became used to it as I became more interested in railways. Given that many children and youngsters appear to listen to pop music at very high volumes I do wonder why they need ear defenders for steam locos! Perhaps they are getting soft?
It was actually heading northbound. However, correct me if I'm wrong, having descended the bank and coasted into Taunton, is it possible that the engines didn't really need to fire up so the pressure just built up from lack of steam required for tractive effort? I also wonder if the presence of a diesel pushing from the back increases pressure valve activation, given it's providing extra power, so less steam is required to achieve the same speeds compared to the diesel not being present?
If they coasted into Taunton, the deisel would only be idling as there would be no need to assist, More than not, the valve would have lifted because the crew would have needed the steam to climb the bank, and once you shut the regulator it's not needed but the pressure is still rising, so the safety's lift, until the pressure drops back.
If anyone happens to be interested, the BTC Handbook for Steam Locomotive Enginemen states that "Blowing off can be avoided by careful management of the fire and injectors. On a modern 4-6-0 locomotive with a tractive effort in the neighbourhood of 26,000 lb, there is a loss of pressure and wastage of approximately 10 gallons of water for every minute the safety valves are open." Interestingly no corresponding figure for coal wastage is given. A BR Standard 5-MT would appear to have delivered a tractive effort of 26,120 lb, so we can guess which "modern 4-6-0" the authors had in mind.
I guess you could work out how much energy is needed to raise 10 gallons of water to around 200C (the boiling point at 225 psi steam pressure), allowing for the heat transfer efficiency (from coal to water) of a typical loco boiler (which a quick bit of Googling suggests is around 60-70%), then translate that into weight of coal of average calorific value?
Then by my calculation, this roughly translates into the wastage of 1 cwt of coal for every 7 minutes the valves are open. Others will know how many fireman's shovelfuls there are to the cwt or kg.
but what about the latent heat needed to evaporate the 10 gall of water water into steam? Shouldn't that be in there somewhere too?
Not necessarily. At a typical boiler pressure of 200psi the boiling point of water is 200C. I think the reason it comes off as steam is because the pressure reduces as it is taken out of the boiler, and the latent heat must be supplied by reducing its temperature accordingly. Not too sure about this though - it's several decades since I did any thermodynamics and most of it passed me by even then...
Thermodynamics isn't my strong suit either, but if we assume the latent heat of vaporization should be included (which is about 1940 kJ/kg at 200C => 87000 kJ for 10 gal/45kg of water), I think that makes it about 12kg of coal.