A fire chief today accused the Fire Brigades Union of "placing the public at risk" by pressing ahead with a planned 24 hour strike.
South Yorkshire's chief fire officer Mark Smitherman said he reacted with "absolute astonishment" when the FBU rejected his offer of negotiation and decided to press ahead with the actions planned to begin at 6pm today.
The stoppage will be the second in South Yorkshire this week and is the latest stage in a long running dispute between the FBU and the South Yorkshire Fire Authority over proposed changes to shift patterns.
Speaking at his Sheffield HQ, Mr Smitherman said he had put a fresh offer to negotiate to the union yesterday which had been rejected.
The fire chief said: "My reaction to the rejection by the Fire Brigades Union of the proposals put forward by the authority yesterday is absolute astonishment.
"I'm amazed the Fire Brigades Union can still continue to refuse to get involved in negotiations.
"As far as I can work out, the authority is meeting all of their requirements regarding the most recent press releases and statements they have made in the media."
The dispute erupted over proposals to implement a 12-hour shift pattern, instead of the current pattern of nine-hour days and 15-hour nights.
Firefighters have argued new shift patterns would present families with problems, especially over childcare arrangements.
The FBU has continually said it will not call off the action unless a threat to sack 744 firefighters as a means of imposing new contracts was withdrawn.
Mr Smitherman reiterated his view that his changes would not affect anyone's pay and all jobs and current levels of fire cover would be maintained.
He also said the firefighters working pattern of two day shifts, two night shifts and then four days off left ample time for family life.
Mr Smitherman went on: "Their (the FBU) actions at the moment are placing the public at risk unnecessarily because there is an option for them to enter into negotiations".
He also said he was "perplexed" as to why the union was taking this stance in the South Yorkshire service.
He said: "At least four others have introduced identical changes and a couple have introduced vastly different and more complex changes to the shift system pattern to what we are proposing here and all of that has been done with the agreement of the FBU."
Mr Smitherman and his assistant chief Jamie Courtney went through their contingency plans for tonight, which will involve 183 staff including senior managers and firefighters who are not in the union.
Asked about what happened during the last 24-hour strike, which started at 6pm on Monday, they said the call-out rate was about normal.
Mr Courtney said appliances were called to two incident which were initially classified as life-threatening but both turned out to be less serious.
He said one was a fire in a bin store at a block of flats which had left a stairwell smoke-logged and the other was a smell of burning at someone's home.
The officer said the biggest incident was a blaze involving titanium at an industrial unit in the Rotherham area which required two crews.
Mr Smitherman said he was concerned about the activities of some of the pickets, especially outside the main Sheffield central fire station.
He said many of those outside the building were not South Yorkshire firefighters and added: "In relation to some of the behaviour I saw, I sincerely hope that those people were not members of the British fire service because there was certainly some activity in isolated pockets where it was obviously designed to intimidate the working members of staff."
The fire chiefs were speaking just a short distance from Sheffield 's main bus station, which was quiet as drivers working for the firm First began the first of two 24-hour strikes in a row over disciplinary action.
Steve Clark, Unite regional industrial organiser, said: "Sheffield has outstanding collective grievances that still need to be resolved, like the company's attitude to disciplinary action."
Strikes were originally set to go ahead in Rotherham, Doncaster and Sheffield over pay but unions accepted an 11th hour offer.
A spokesman for the FBU said the latest offer was simply a "rehash" of what had been previously rejected and Mr Smitherman's claim of "astonishment" at the rejection was "false posturing, nothing more than a PR pose".
He added: "Those putting the public at risk is a fire authority threatening to sack all its firefighters so they can rip up their contracts of employment.
"If it withdrew that threat there would not be a strike tonight.
"The fire authority has been hell-bent on confrontation. It has rejected all suggestions from the FBU and from local MPs about how to resolve the dispute. It has rejected every attempt at compromise the union has put forward."