Passenger watchdogs, politicians and a fire expert are among those calling for an urgent investigation after at least five major incidents since January, including in Glasgow city centre last weekend in which one person was taken to hospital.
They follow five passengers on a St Johnstone football supporters’ bus receiving hospital treatment after it caught fire on an A9 flyover near Auchterarder in November.
One of those injured said he had to break open a window to escape because he thought the vehicle was going to explode
Jayson Dempsey told STV: “We came home from hospital and never slept.
“You just have all these horrible thoughts running through your head of what could have happened.”
The Fair City Saints supporters club said: “The quick thinking of the committee members and others on the bus plus the driver ensured everyone was off as quickly and safely as possible and everyone made it home to their loved ones.
"This could have been a lot worse but it’s not worth thinking about.”
A First Glasgow double decker bus went on fire in the city’s Renfield Street eight days ago, for which a 54-year-old man was treated in hospital.
Another of the operator’s double decker buses caught fire in Drumchapel on 6 April.
In March, school pupils were forced to evacuate their Stagecoach-operated service when the double decker went on fire near Inchture between Perth and Dundee, 11 days after a First bus single decker caught fire in Gorgie Road, Edinburgh.
A Lothian bus caught fire on the Edinburgh City Bypass in January.
Guillermo Rein, professor of fire science at Imperial College London, said buses were “significantly riskier” than cars, trains, ships or aircraft, mainly due to their less stringent fire safety requirements.
He said: “I wish a thorough investigation was arranged to look into causes, trends and solutions.”
Robert Samson, senior stakeholder manager at official passenger watchdog Transport Focus, said: “Passengers will be concerned and want assurances that operators are looking into these incidents as a matter of urgency.”
Unite, which represents bus workers in Scotland, said: “While we have seen these very serious incidents and noted them, it's not something that's being actively raised by our members as a concern.”
However, the Rail, Maritime and Transport union, the main bus union south of the Border, described the number of fires as “unacceptable” and said it had raised the issue with the body representing bus operators.
General secretary Mick Lynch said: “We have written to Confederation of Passenger Transport to find out what they are doing to deal with this serious health and safety issue.
"I believe the UK bus industry appears to be sleepwalking its way into a situation where one day there will be a catastrophic incident.
“Evacuation is a major concern as the customers could be disabled, less abled, parents with small children or pushchairs, visually impaired, deaf, elderly or infirm.”
Scottish Labour transport spokesperson Colin Smyth said: “These incidents are deeply worrying.
"While taking the bus remains one of safest forms of travel, one incident is one too many so it's vital that every fire is reported by firms and fully investigated to cut the future risk."
Scottish Conservatives transport spokesperson Graham Simpson said: "We need to get to the bottom of why there appears to be as many as here are.
"There are suggestions that slow traffic speeds could be a cause and that the design of modern buses could be a factor, but we need more work to establish if that's true.”
Duncan Cameron, managing director of First Bus Scotland, said: “We can confirm there has been three fire-related incidents on First Bus vehicles in recent weeks.
"Each of these incidents involved completely independent issues in separate parts of the vehicle.
“The safety of our customers, drivers and the public is our first priority when delivering our services and we would like to praise the quick and safe responses by each of the drivers involved."
Stagecoach said its vehicle fires involved “completely separate component failures - as can occur in cars and any other motor vehicle - and there is no connection between them”.
A spokesperson said: “The safety of our customers, employees and other road users is our absolute priority and close to all journeys get customers to their destination without incident.
"We take any incident of this nature extremely seriously and always carry out an in-depth investigation which includes determining the root cause and immediately taking any corrective action needed.
"We also share the appropriate information with the Driver and Vehicle Standards Agency (DVSA).”
A DVSA spokesperson said: “Our priority is protecting everyone from unsafe drivers and vehicles.
"We have put effort into making sure bus companies report fires and other accidents as they’re required to.
“We ensure the causes of fires are understood, working with others to investigate as necessary.
“Where we spot trends, we work with the vehicle operators and manufacturers to understand the issues."