This article was reproduced with the kind permission
of the British Broadcasting Corporation
6 November 2007, 10:59 GMT
Part of the first floor of the plant in Atherstone-on-Stour, Warwickshire, is having to be rebuilt, slowing the progress of the search teams.
Firefighter Ian Reid, 44, died in hospital after being pulled from wreckage of Friday's fire.
Darren Yates-Badley, Ashley Stephens and John Averis are still missing.
Up to 200 people are involved in what fire crews have called the "immensely frustrating" search of the packing plant, which is the size of four football pitches.
The search for the men began on Sunday and 12 search teams have so far gone 20m (22 yards) into the building.
They are thought to be 80m (88 yards) away from where they think the missing men are.
These professional men were doing their job of controlling a raging
fire - with a tragic outcome - but their actions remain those of heroes
Firefighters worked through the night, continuing their search
The building is structurally unsafe and special monitoring equipment has been put in place around it to check for movements. A steel girder fell during the search on Monday.
Police forensic teams are also inside the warehouse investigating the cause of the fire, which is being treated as suspicious, and items are being removed for analysis.
Jon Hall, assistant chief of Hereford and Worcester Fire Service, which is leading the search, said: "We are monitoring the situation minute by minute. The desire to see this through to the end is unstinted."
He added: "Due to the state of the building and the conditions crews are having to work in, we can no longer say how much longer this operation will take.
"We will not stop operations until we retrieve the Warwickshire firefighters who are still in the building."
He said 150 staff who worked in the building had all been accounted for.
Outside Alcester Fire Station, where two of the firefighters were based, candles have been lit and floral tributes laid.
Mr Reid had worked for Warwickshire Fire Service for four years and was based in Rugby and Stratford-upon-Avon.
Mr Yates-Badley, 24, was based at Alcester and had only recently married his wife Faye.
Mr Averis, 27, was based at Stratford-upon-Avon and had been with the fire service for three years, previously working as a Ministry of Defence firefighter at Marlborough Barracks.
Mr Stephens, 20, was the youngest of the men and was also based at Alcester. He leaves behind a fiancee, Emma Crocker, with whom he had a three-month old son, George.
In a statement, Mr Stephens' fiancee, mother Sharon and father Paul, said: "Ashley was a wonderful loving father, fiancee, son and brother and he will always be in our hearts."
Mr Yates-Badley's wife, Fay, and his parents Mandy and Stephen Baylis, said he was "larger than life".
"Darren treated everyone equally and with the same kindness," they said.
"We didn't realise the impact that Darren had on other people's lives and he is our hero."
Warwickshire's chief fire officer William Brown praised all the men.
He said: "Our work involves us in often difficult and sometimes highly dangerous call-outs.
"These professional men were doing their job of controlling a raging fire - with a tragic outcome - but their actions remain those of heroes."