Two men were rescued from a fire which damaged much of a first-floor flat in Hayes in a suspected arson attack.
Emergency 999 fire brigade control officers stayed on the phone to one of the trapped men until firefighters arrived at the maisonette, in Stratford Road, on Thursday morning (June 23).
They gave him "vital survival advice" and helped him calm down by telling him to put blankets by the door and open a window.
Around half of the first floor of the maisonette was damaged by the fire and the roof was slightly damaged by the blaze.
Police were called by the London Fire Brigade at around 5:15am and requested police assistance as they believed it to be suspicious.
A Metropolitan Police spokesman said: "Officers arrived and arrested a 20-year-old man inside the property on suspicion of arson.
"London Ambulance Service also attended and the suspect along with a 42-year-old man were taken to hospital to be treated for smoke inhalation."
London Fire Brigade watch manager Paul Alden, who was at the scene, said: “When firefighters arrived a man was sitting on a window ledge on the first floor at the back of the building talking to control room staff on a mobile phone and another man was inside the maisonette.
"Firefighters wearing breathing apparatus entered the front of the building and rescued one man from inside the maisonette using an internal staircase.
"Fire crews used a ladder at the back and brought the other man from the window ledge down to safety.
"After the two men had been rescued, the fire was quickly brought under control.”
Mr Alden gave valuable future advice for homeowners as, in this case, the maisonette didn't have a working smoke alarm.
He added: "Having a working smoke alarm and testing it regularly is essential, as they can buy you vital seconds to escape in the event of a fire.”
The cause of the fire is under investigation by LFB and detectives from Hillingdon CID.