BBC News Online Health Staff
The divers knew they risked the bends
Phil Macdonald and Tony Smyth were 43 metres underwater when they had to make a split-second decision that could literally have meant life or death for the diving buddies.
A problem with their ascent had sent them slumping back to the sea bed, and left them dangerously short of air.
They had to decide whether to rise to the surface quickly, missing a vital decompression stop - and risking the bends - or take the stop and risk drowning as their meagre air supply ran out.
The experienced pair decided to risk the bends and make their emergency ascent, knowing that in a worst-case scenario they could spend the rest of their lives in wheelchairs.
Caused by a diver coming to the surface too suddenly
Nitrogen bubbles enter the blood and tissue and attack the nervous system causing bone and joint pains
The hyperbaric unit helps dissolve bubbles, speeding the recovery of damaged tissues
They had been diving near a wreck off the coast at South Shields when the accident took place, and needed to be airlifted by a RAF Sea King rescue helicopter to the special unit in Hull.
"When we decided to come up we got to 20 metres up when we decided to deploy a marker, but as we did this we started sinking back down," said Tony.
"We sank right down to the sea bed so we had to ascend again and realised we were very short of air."
"We both carry emergency cylinders but we were still short of air and when we got to the surface we had very little air left," said Phil.
He added: "We did think about getting the bends as we rose to the surface, but as we were running so low on air we knew we had to avoid drowning.
"When we reached the boat I was suffering from pins and needles in my legs, which is a symptom of the bends - so they gave my oxygen and called the coastguard to take us to the hyperbaric unit."
The helicopter had to fly to the unit, at the BUPA Hospital Hull and East Riding Hospital, at wave-top level because flying any higher might have increased their risks of suffering the bends.
Luckily Tony was asymptomatic, but because Phil had possibly suffered during the ascent both had to spend nearly five hours in the chamber to ward off any potential problems.
"Although I had not got any problems there have been cases of people going away on holiday and then getting problems when they return home," said Tony.
But the incident has not put the pair, who are both firemen with the West Yorkshire force, off diving and they continue to go regularly.
Phil and Tony are among 60 divers treated each year at the hyperbaric unit, which counteracts the effects of the bends by exposing sufferers to high-dosage oxygen.
Gerard Laden, technical director of the unit, said that as diving has become more popular over the last 30 years the demand for units like this has grown.
"Everybody knows someone who has been, or who goes diving, and the numbers of it have increased significantly.
"With that increase the numbers using the unit have also gone up."
The hyperbaric unit was set up five years ago and expected initially to treat a maximum of twenty patients a year, but it soon became clear that the figure would be nearer 60.
Patients are taken to the unit from costal dive sites around the UK, as well as freshwater quarries.
The chamber helps the body recover
Symptoms can range from minor ailments such as pins and needles or aches and pains to complete paralysis from the chest down.
"We see people who have suffered major disabilities as a result of the bends such as being paralysed from the mid-chest down and then left wheelchair bound."
But Mr Laden said the UK system, which uses a help-line to advise divers and tell them where to seek help, was one of the best around.
"This is I suspect the best system in Europe using two simple telephone numbers and all at no cost."