Hertfordshire Fire and Rescue Service is waving goodbye to Reqs, Britain's longest-serving fire investigation dog, as he retires from the service.

The black Labrador has been using his impeccable sense of smell to detect accelerants like petrol at the scenes of fires in Hertfordshire and the wider eastern and south-eastern regions for almost 11 years, making him Britain's longest-serving fire investigation dog.

Reqs, 11, has attended around 500 incidents since joining Hertfordshire Fire and Rescue Service in 2012 as a one-year-old. Together with fire investigators like his handler Watch Commander Nikki Harvey, he has provided crucial evidence in high-profile investigations, including for arson and murder, resulting in over 250 years of imprisonment for convicted offenders.

Nikki said: "We are called to the scene of any serious fire that crews believe to be deliberate or suspicious, or where the cause is not immediately known, especially if there has been a fatality at the scene.

"Reqs gets involved as soon as it is safe. I'll go through the scene first to check that it has properly cooled down with no visible sign of smoke or embers and that there aren't any hazards that could harm him. He gets to work using his best tool – his nose – to locate any potential accelerants like petrol that might have been used to deliberately start a fire. That's when the human fire investigators like myself can take a closer look while Reqs enjoys a reward – his favourite tennis ball!"

Reqs has become incredibly popular online, where he's amassed more than 10,000 social media followers alongside his protégé Loki, who he will be passing the mantle to. He is hugely popular with Hertfordshire residents too, through his regular appearances at fire station open days and countless visits to schools and clubs. He has also brought comfort to many families who have sometimes lost everything in a fire.

"His interactions with children, especially those who have had fire in their home, leaving them quite frightened, can be therapeutic. The distraction of stroking him and throwing him a ball can give comfort and reassurance to those affected by traumatic incidents," said Nikki.

After years of hard work, Reqs can look forward to putting his paws up. He'll remain with Nikki as her pet dog and will still come along to community events like open days alongside Loki, especially if it means getting to steal a few sausages from the barbecue.

Nikki said: "I'll miss the nice cuddles he gives at the end of a job, especially if we've been to an upsetting or distressing incident. He's my best mate and I love him to bits – while it's the end of an era in some ways I'm so pleased he'll still be around and part of our very special community, and I know that Loki will carry on doing a great job in his paw-steps."