A student needed surgery after fracturing his spine at the Flip Out Chester trampoline park.
George Magraw, 21, from Ellesmere Port, has been told he will need months to recover from the injury.
The University of Leeds student had jumped from a 4m-high platform into a foam pit during a visit on Wednesday (February 1).
Flip Out admitted there had been 'a number of incidents' on the same day but said they had an 'excellent safety record' and had launched an investigation.
George’s brother Phil said: “Either there was insufficient foam in the pit or it’s too old to make sure he has a soft landing.
“He landed on his bum and it’s shattered a vertebrae in his lower back. They gave him an X-ray and said the disk had pretty much disintegrated.
“George is in a lot of pain and they said after the surgery he will need months to get back to normal or there could be complications.”
At Flip Out there are three platforms of increasing height from which guests can jump into the foam pit.
Safety advice to avoid injury is to land in a ‘seated’ position as George did.
He was taken to the A&E department at the Countess of Chester Hospital where Phil said staff told him they had dealt with a number of injuries from the park.
After scans revealed the extent of his injuries, the 21-year-old was transferred to the Walton Centre in Liverpool for specialist care.
George was undergoing the surgery on Friday which will see his shattered vertebrae replaced by a metal disk.
Phil said: “With this kind of injury you just can’t tell what will happen.
“When it happened Flip Out offered to call an ambulance and had him fill out an accident report. As far as they were aware he left with a back injury."
Flip Out opened in Chester, their second UK site, in December last year.
The 40,000sq ft park at Chester Gates Business Park has been called the biggest in the world.
A Flip Out Chester spokesman said: "We can confirm that a number of incidents took place on Wednesday.
"An immediate investigation was launched and we are still trying to establish exactly what happened.
"Since opening in December around 80,000 people have visit Flip Out Chester and we have an excellent safety record.
"Safety is our number one priority and we strive to ensure that everyone who visits can enjoy all of the activities in a safe environment."
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