Plans to change 999 emergency cover in the South West has been confirmed by health bosses.
Unions claim there will be no crew cover when staff take breaks
A management draft document by Westcountry Ambulance Trust (Wat) says the changes will mean more resources and increased flexibility.
Some ambulance stations will close and others will lose 24-hour staffing.
Senior managers say patient care will not be compromised, but the Unison union has repeated warnings the changes could be dangerous for patients.
The trust said the changes will put more emphasis on rapid response vehicles and part-time first aiders, called emergency care assistants, who will work alone.
The changes also mean some places like Taunton in Somerset, Torquay in Devon and Penzance in Cornwall will get more cover.
Mike Willis, chief executive of Wat, said: "The emergency care assistants are people who have been trained to respond.
"We wouldn't allow people who are not trained to attend the public."
Some ambulance crews have backed Unison, saying scaling down 24- hour cover will put patients at risk.
One staff member said: "Lives will be lost. Managers are making decisions based on saving money.
"When people dial 999 they may get someone who won't have a stretcher, can't administer life saving drugs and can't take them to hospital.
"The trust will have met the eight minute response time but it won't be able to deal with the emergency."
But Mr Willis said they will be backed up by emergency response vehicles from other areas.
Staff are already being balloted by Unison over the possibility of taking industrial action.
Ambulance staff said pay is not the contentious issue, because some may be better off, but the issue of patient welfare is of serious concern.