The photographer was driving to his studio for a meeting when he realised the fire on the horizon was at the farm where it was based.
“It was about 150 metres (492ft) from my front door, and I quickly cancelled the meeting and thought, ‘I’m not happy with where the wind is going on this’,” he said.
Johnson began removing some of his more expensive kit from the studio and was putting it in the van when the explosion took place.
A unit housing fertiliser had exploded.
He said: “It blew me into the door and I just ran to the van, dropped the bit I went back in for – maybe it saved my life, I don’t know.”
As it happened: Twenty firefighters taken to hospital after major Essex explosion
The photographer was shocked to see his studio roof had completely caved in.
Having driven to a safe distance, “I pulled over, and I was just in shock and started to shake”, he said, although he was reassured after an ambulance crew checked him over.
Johnson managed to cover his wedding booking on Saturday, praising his “amazing assistant” James Musselwhite for driving from Portsmouth to help him out.
“I’m in a little bit of shock still, to be honest,” he said.
“I’m completely unscathed apart from a bit of a dodgy ear from the pressure – but how I’ve got away with it unscathed I have no idea.”