Yeah, but if you forgot to turn the valve back off after a refill ... Later models sort of "built in" the reserve tank with a wedge-shaped line after the "E" to show you were on the way to running out out. (We used to sometimes new drivers the "F" stood for "Fill 'er up" and "E" stood for "Enough").
I had a quick soldering job holding up progress on my project. Unfortunately, the only free soldering station in the lab was faulty. The light on the base unit was lit, indicating that it was powered but the iron did not heat up. So, I fiddled around with it until it worked. Pleased with myself, I waited for it to heat up. I was just about to start my soldering job when a technician turned up, helpfully telling me that the soldering station did not work. I said it did. He said no it didn't and I guess he wanted to be proving his point rather theatrically. I only had time to start my next sentence with "but..." while he snatched the soldering iron out from its holder and with a smug grin on his face, he pressed the business end of the iron in his palm and closed his fingers on it. There was this searing sound, a bit of smoke rising, closely followed by the unmistakable smell of burning flesh. I think he learnt a valuable lesson in safety.
This reminds me of when I was working on a project which involved a relatively high power piezo-electric transducer. One suitable for the job used a much lower operating frequency and higher power than what the company itself had ever produced. My request to purchase a suitable transducer was denied and the VP of engineering decided we could make one of our in house units work by mechanically loading the piezo ring to lower the resonant frequency.
His plan was to machine a metal ring which would be heated and pressed over the cooled (approximately 3" diameter, 2" high, 1/4" thick) piezo-electric element, which would create a tight fit at a common temperature. The metal ring was in the oven and I had obtained some dry ice which I was bathing the ceramic ring in. I used some handy needle nose pliars to pick up chunks of dry ice and place them in intimate contact, both inside and outside the ring.
Focussed on the task at hand, I neglected to think about the ceramic ring contracting from the cold and the resulting potential voltage developing across the metalized electrodes on the inner and outer surfaces of the ring. Lo and behold I managed to get my hands across the voltage, resulting in my arms flailing out to the side, losing the needle nose plairs, and almost hitting my coworker who was observing. I instantly realized what had happened and luckily the shock was short lived from a dc source.
The experiment did lower the resonant frequency but killed the efficiency, resulting in no net gain. We ended up buying the proper transducer when all was said and done.
In the late 80's, the company I worked for was shipping systems internationally, so we had a fridge sized high current 120v/60Hz to 240v/50Hz converter. One of the techs was testing a new system, when out of the corner of my eye I saw the lab illuminated by an intense actinic blue flash and heard a loud Mrrrzzzphhssttttt! There happened to be a length of 2x4 handy (from a shipping crate being built) which I grabbed, so as to, should it be necessary, separate the tech from the burning (?) converter. No-one was injured, but the converter was a charred wreck, and was never repaired. We found a better way to test the systems.