Light rail service in Lakewood restored after fire extinguished

(AP Photo/David Zalubowski)
<p>A light rail train car in Denver, Colorado. </p>

A fire and explosion interrupted RTD's 'W' line light rail service for much of Wednesday afternoon.

Service was restored in time for the evening rush hour after police found the source of the explosion -- a smoldering mattress ignited propane tanks near the tracks, Lakewood Detective Timothy Marquez says.

Emergency personnel discovered a water drainage tunnel that runs underneath the street to deal with excess water. When police and bomb squad personnel entered the tunnel, they "observed what looked like a transient camp".

Marquez said that the mattress "somehow caught on fire", which then caused two small propane cannisters to heat up.

It is not known if it was intentional or accidental, and police are investigating who was in the tunnel.