Specialised help has poured in from across Britain to fight the blaze but few crews were available for fires elsewhere in Hertfordshire, a union spokesman said.
Spokesman Duncan Milligan said at times just one crew was being dispatched to house or flat fires where normally up to three would attend.
Mr Milligan said: 'The resources in Hertfordshire are desperately stretched. They have had to deal with a flat fire in Stevenage with one fire engine.
'Normally you would have at least two and possibly at least a third one.'
At another fire at a house in Radlett, he said: 'They were desperately stretched to try and get anyone to it.
'The point being, yes there is a major incident but there is the fact that everything else has to be dealt with as well.'