The fire was reported about 1 a.m. Dec. 17 at the Sims Metal Management plant at 699 Seaport Blvd. An on-duty employee at the facility reported the fire after hearing a loud explosion and seeing the fire ignite in a stockpile of metal recyclables, said Lt. Sean Hart.
Police and fire investigators are continuing to review surveillance footage, according to Hart.
Firefighters fought a similar blaze at the Sims Metal Management plant Nov. 10 in which flames ignited in a heap of crushed cars and other large materials, according to fire officials. Hart said the two fires are not believed to be related.
Redwood City Fire Marshal Jim Palisi said the Nov. 10 fire was not deliberately set but said investigators could not find its exact ignition source.
Firefighters also battled a blaze at the same recycling center in April 2007. The Bay Area Air Quality Management District levied public nuisance violations for the 2007 and November fires due to large quantities of contaminates that annoyed or caused a nuisance to the public.