I thought this post needed resurrecting. 
Here are my two ADR (nearly) horror stories… 
#1.
The first story relates to the ‘military’ so I have to be careful. 
The military needed several thousand tonnes of various types of explosives moving from a base to the docks for loading onto a ship in preparation for a military exercise to be conducted in a foreign country.
Our job was to move the stuff as civilian contractors with unmarked (no orange boards) trucks in convoys of 10 artics at a time. We weren’t allowed to be present during the actual loading, so we dropped the trailers for tuggys to load and they’d later re-spot the trailers where we’d been told to leave them. The idea was that we didn’t know the contents until we opened the trailers at the docks. The paperwork was in sealed envelopes and soldiers were passengers in the front and rear trucks in each of the convoys.
After loading, each convoy headed to the marshalling area and the drivers had to go into a portakabin to receive a briefing and our sealed envelpoes. On this particular occasion, we’d got to the marshalling area and switched off our engines. I was walking towards the portakabin with another driver when we noticed a large amount of extremely smelly blue/black smoke coming from underneath the cab of one of the tractor units. Within seconds, there were soldiers and other drivers running for cover behind the earth mounds surrounding the marshalling area. 
The solution seemed quite simple to me, I just went back to my truck to fetch a spanner, then I disconnected the batteries on the faulty truck. The smoke stopped quite quickly after that. I reasoned that the problem was caused by a short circuit of some kind, so disconnecting the batteries solved the problem. We disconnected the susies, wound down the trailer legs and pulled the pin, then a tuggy towed the faulty tractor unit away and a substitute tractor and driver was brought from the pool of vehicles that had done the last run.
When we got to the docks, I discovered that the load on the trailer that was to have been taken by the faulty tractor unit was in fact three large bombs of the type that the military would drop from an aircraft. IIRC, the bombs were about 2’ in diameter, about six paces long and about 3 tonnes apiece. 
#2.
I was driving an artic tanker carrying about 34,000 liters of propane from Stanlow refinery to a gas storage depot in Llandudno. This was a regular run for me, and it was a routine job that I did three times a day on at least three days per week. On this occasion, I’d arrived at the depot and proceeded to the discharge point. I’d connected my earth bond cable to dissipate any static electricity, before commencing to connect my delivery hoses. Company policy dictated that I could connect my delivery hoses and get set for the delivery to commence. At that point, it was company policy to have me wait for a technician to be present to give permission for the unloading to commence.
After the technician had checked everything and opened the valves of the receiving tank, he told me to start my pump and open my last valve, which allows the propane to flow from my tank into the receiving tank. This all went by the book in a routine way. Until the job went wrong. 
Once discharge is underway, the technician goes back to his normal duties, leaving me to monitor the pumping operation. After about 10 minutes of pumping, a shear coupling__**__ broke, resulting in a white fog of liquid propane squiting about 15’ straight up into the air.

Those who have done the ADR course know all about what might happen next, if there’s an ignition source anywhere nearby…

I was far more scared by this than the short-circuit in my first story, because there wasn’t much actual danger in that, but a propane leak of this size is a completely different story…
Let’s just say that I was on my toes so fast that Linford Christie wouldn’t have caught me. 
As I ran, I pressed my ‘panic’ button, which is actually a radio ‘remote’ that’s designed to shut off the the truck engine and discharge valves from a safe distance. Fortunately, there were no ignition sources nearby, and the propane cloud dissipated safely.
Once it was safe to re-enter the unloading area, we discovered that the shear coupling hadn’t completely broken in two as it is designed to do. That’s why the leak was much larger than it should have been.
** A shear coupling is a safety feature consisting of two spring-loaded valves fitted in opposition to each other. The joint is designed such that the ends of both valves protrude from their respective pipe flanges, the flange joint is then bolted together forcing the valves to hold each other in the open position. The idea is that, if the vehicle were to be driven away with the delivery hoses still attached to the discharge point, this coupling breaks in two, the two valves both then snap shut, but with one valve in each piece of pipe there’s not supposed to be any serious leak if the joint breaks. The two valves are usually secured by three bolts that are calculated to be only just strong enough to hold the joint together. Imagine the shock on the technician’s face when he saw that only one bolt was holding the joint together, hence the huge leak. 
I’m no technician or engineer, but methinks that the bolts were a bit too strong. 