Chelsea firefighters were dispatched to check for alarms on Revere BBeach Parkway.  Companies arrived to find heavy smoke showing from a commercial building and the first due engine requested the box struck.  Companies made an aggressive interior attack but were drawn back by heavy fire conditions.  Command struck a 2nd alarm and eventually 3rd,4th and 5th alarms were all struck bringing in multiple mutual aid companies to the scene and to cover the city.  Multiple master streams and big lines were used to knock down the main body of fire.  Companies remained on scene for several hours in a defensive operation.