That will T-cut out no bother.
It always amazed me how many bulkers blew the loads without proper earthing. Places like flour mills, bakeries, etc knew the risks and provided decent earthing points for delivery drivers to connect to. However, although they must have known the risks associated with fine powders viz-a-viz static electricity, I could count on the fingers of my hands the number of quarries, concrete plants and even cement works equipped with the proper earthing points.
As already mentioned, it could have been many things that have gone wrong and may have been down to a plant maintenance issue. I have seen the filters blow out of the top of the storage silo because they were damaged or set at the wrong pressures. I have seen a tested delivery hose tested so hard that it blew the ends off.
I have seen warning alarms disconnected because they kept going off. In one case one of the silo filters blew over the top of the factory roof and landed on a car, this thing weighed about 300kg
It could have been a land based blower that someone had messed about with the air taps or PRV.
2 bar pressure / 29psi in a bicycle tyre is not that much but increase the size of that tyre to 30 feet across it that is some hellish volume. You may have 2 bar in the tanker, 1.5 bar in the delivery hose dropping to .5 bar at the top of the ground silo. The silo filter has to get rid of that pressure at the same rate to stop an explosion
I worked for Huktra when I started on tankers and one of their Belgian subbies lost his head when the lid came off and hit him under the chin, they never found his head.
Four or five years ago when I was at VDB or Tielt a French silo tanker loaded with wheat caught fire, the pressure rose inside the tank and while the fire brigade were there it split wide open.
Don’t mess with tankers, valves or factory pipework if you don’t understand what you are doing.
Powder explosions and static electricity have already been mentioned, there is more to tank work than simply being a prima donna 
It could have also been a self clean that wasn’t very clean!
I don’t know anything about these things so perhaps this is a stupid question, but why don’t these trailers just have safety valves like steam railway engine boilers?
Harry Monk:
I don’t know anything about these things so perhaps this is a stupid question, but why don’t these trailers just have safety valves like steam railway engine boilers?
They do, but they could be blocked with cement, damaged, blanked off or just not adjusted or serviced.
You can either explode or implode a tank with a faulty PRV. Both expensive, both dangerous.