A railway enthusiast who died after his head hit a signal gantry as he leaned out of a speeding train was so badly injured that he would not have been aware of the accident, an inquest has heard.

Simon Brown, 24, was killed as he stuck his head out of the window of the guard’s compartment on a Gatwick Express train. He collided with the gantry between Balham and Wandsworth Common stations in south-west London on 7 August last year.

Recent Network Rail safety checks had found the clearance between the top of the window and the gantry was as little as 68mm as trains moved past at speed, the hearing at Wandsworth coroner’s court heard. The gap was deemed acceptable for an existing structure.

Medics responding to the accident after the train arrived at Wandsworth Common station deemed that Brown’s injury was “incompatible with life,” the hearing heard. He was pronounced dead at 6.47pm.

Kirstin Duffield, who witnessed the accident, said that when she saw Brown he was still breathing. “I noticed a lot of blood and there was major trauma,” she said. “I turned around to stop my daughter from seeing.”

She told the girl to pull the emergency cord, stopping the train, and sent her to fetch the driver, whom she then spoke to. “I explained the situation, realising what had happened was not survivable,” Duffield said.

“Rob, one of the paramedics, told us that the male [Brown] would not have known what was going on because of the kind of injury,” she added.

Brown, who had just taken a job as a commissioning engineer for Hitachi Rail Europe, had been travelling to work for a night shift on the 17.05 service from Gatwick to Victoria.

He was a lifelong railway enthusiast who had volunteered on West Sussex’s Bluebell Railway in his youth and turned his enthusiasm into a career by taking a four-year engineering apprenticeship with Southern.

During the inquest hearing, friends and relatives sought to scotch suggestions that recklessness contributed to his death. Surveillance cameras on the train proved to be faulty, leaving no clues as to how Brown’s head came to be out of the window at the moment it struck the gantry.

The inquest heard that risk assessments for the Class 442 train that Brown was on had not taken into account the potential hazard of a passenger putting their head out of the window, despite the train having two opening windows and operating without a guard.

Andrew Walker, a friend of the victim’s mother, Jane Street, asked whether it had been a failure of risk assessments to not take into account whether passengers standing by the open window could be “thrown off balance by the movement of the train”.

In a statement read out by the coroner, Street said she hoped her son would be “vindicated” by the findings of an investigation by the Office of Rail and Road, a health and safety watchdog. “Simon was not reckless nor ignorant of the dangers,” she said.

A postmortem investigation found no traces of drugs or alcohol in Brown’s body.

It also emerged during the inquest that Network Rail did not routinely share information with train operators about structures close to passing trains, even though such measurements are taken annually. The section of track where Brown died had been subject to remedial work in February 2015 after a survey found some structures at risk of hitting passing trains.

Relatives of Brown, from East Grinstead, West Sussex, criticised Southern for not securing the windows on the Class 442 trains on the Gatwick Express route. They said there was no need for opening windows on the trains because the route is driver-only operated.

In a statement, Brown’s family said: “Too often today companies operate for the shareholders or ‘fat cats’ filling their pockets at the expense of safety, as other recent incidents have indicated and I believe that Southern Trains and their parent company have lost sight of what should be their first concern, passenger safety. They have no reputation left to salvage after the last year of appalling passenger service, they have proved beyond doubt that passengers come at the bottom of their list in priority, whilst shareholders have received increased dividends.”

Concluding with a narrative verdict, coroner Dr Shirley Radcliffe said: “It’s not possible, for lack of CCTV footage, to know how Simon came to have his head out of the window, whether he did so voluntarily or involuntarily; but there is no doubt he struck the gantry and sustained a very, very serious injury to his head, such that the paramedic said he would know nothing about it.”