What happens when lightning strikes a modern wind turbine blade?
The extinguisher you used was probably a class ABC. Flammable metals like Mg are a class D fire. Some of the ingredients in an ABC (I don't know which) will react with Mg. I kept a couple 500 g bottles of class D in the stock room, just in case. You might considering doing the same, but get more than I kept (a high school lab). All that aside we managed to cut off the power and use water. Water reacts with Mg as well. The Mg was probably used up by the time the water came on and you put out the secondary fire. Glad it didn't burn down the place. The usual fire department reaction to an Mg fire is to let it burn out while preserving the surrounding structures.
Disposable detectors are battery operated only. Wired detectors cannot access the quick disconnect through the battery compartment. You have to twist the body of the detector from the mount, which will then drop out and dangle by the AC wires. You then simply pull apart the connector. Take the detector down, remove the battery, install a new one. Then reconnect the AC connector, twist the body back into the mount, and you're done. Actually, there is no need to physically disconnect the AC. Just open the battery compartment and replace the battery. That's it. No danger, no shock, no risk. The ONLY concern is to make sure the battery polarity is correct. Otherwise, the detectors will consider it to be NO battery and continue to beep.
