A raging fire completely destroyed the ground floor of a property after smoke detector batteries were removed.
Emergency services rushed to a property in Leverstock Green Road, Hemel Hempstead to tackle the fire, as the blaze took hold at 6.49pm on Saturday evening.
One casualty, a man, was treated for smoke inhalation by fire and ambulance services at the scene.
He was then taken to hospital.
Two engines from Hemel and one from Kings Langley fought the blaze, which was extinguished by 7.16pm the same night.
The public are being urged to make sure they have functioning smoke alarms following the incident.
A spokesman said: “Smoke alarms were present but all the batteries had been removed so had the fire been during the night the outcome could have been very different.
“We would like to remind the public that smoke alarms save lives.”
One witness said: “I saw fire engines racing there on Saturday night before spotting a massive fire coming from a home.”
Another said on social media: “Why do people take batteries out?
“It’s an expensive and shocking way to learn a lesson.”
In the case of an emergency always call 999.