Clouds of thick smoke are already billowing from the door and windows by the time the first fire engine pulls up outside the Abbeyfield care home in Rickmansworth.
Quickly, two more follow as what had just moments earlier been a peaceful street was transformed into a hive of activity as firefighters unfurled hoses and donned breathing apparatus ready to search for the eight people trapped inside.
Working with speedy professionalism crews began to extinguish the imaginary fire while searching the network of rooms and corridors inside the beautiful but tired-looking detached Victorian house for survivors.
Only the metal cladding over the downstairs windows and a sign warning off would-be burglars gives it away that this home has been vacant for the past year, the inside will soon be gutted and re-fitted as a children’s nursery.
This is in fact a joint training exercise involving crews from Rickmansworth, Garston, St Albans and Hemel Hempstead and the venue for the day has been loaned to them by Natasha Kirby of Boys & Girls Nursery.
"We bought the building last year and Sean (Goode, watch commander) contacted us to ask whether they could use it," she said.
"The building is empty while we sort out planning so we were happy to let them do it.
"It is quite a surreal experience to see your building smoking but it’s great because it’s something that helps the local fire service."
In this instance, watch commander Goode was playing the role of a member of care home staff who had a plan of the building but could give the crews fighting their way through the stage smoke no help as to where the prosthetic dummies were located.
All eight were found and rescued in a successful two-and-a-half hour training exercise which had taken months of planning and liaising between the fire service, Three Rivers District Council, Herts police, and the East of England Ambulance Service to organise.
Watch commander Goode said: "It was a fantastic exercise, absolutely brilliant.
"I spoke to the crews at the end and we are all so grateful to the owners for allowing us to use the building.
"We train every day but we are so short of realistic places to train, particularly larger buildings like this one.
"We often use the smoke tower at Watford but you get so familiar with it that it becomes less helpful."
Watch commander Goode added that fire crews are always looking for new locations to train in south west Hertfordshire and anyone wishing to offer a building should contact their local fire station.