Timber Beam Upgrade - Welded Splice Connection - FIre Hazard??

Here's my problem, I have an existing facility that needs to reinforce its existing 6" x 12" timber beams due to failure. My proposed method is to attach steel channel shapes along the sides and bolt (6) at various locations and fasten at the ends with angles. However, the contractor building the project has indicted that he needs a spliced conneciton for the channels. The current 20'-0" length is impossible to fit in the building's current geometry. My spliced design as of know has a plate attached to both ends of the channels and welded all around. My concern is that when welding the heat buildup on the steel could could cause the wood to catch fire? Is this possible and are their preventative measure to be taken? This has to be a field weld and not a shop weld. My other option is to have a bolted spliced connection, but this is also quite difficult.