Batley flat blast: Gas cylinders thought to be cause
An explosion at a flat that injured five men is believed to have been caused by a "large number of small flammable gas cylinders", said police.
The victims, aged between 35 and 39, suffered burn injuries in the blast on on Hick Lane, Batley, on Wednesday.
It was initially thought a mains gas leak could have been to blame.
Forensic testing would be needed to establish how the cylinders ignited and if any criminal offences had been committed, said West Yorkshire Police.
A police cordon has been in place around of the building while investigations continue.
Det Supt Pat Twiggs said: "We can confirm the explosion was not caused by a mains gas leak or any utility issue.
"A large number of small flammable gas cylinders in one of the flats is believed to be the source of the explosion.
Emergency services were called to the two-storey block of converted flats at about 18:45 GMT on Wednesday.
Witnesses are still being sought by officers.
West Yorkshire Police said they "anticipate being able to return the premises to the control of the owner" later on Saturday.