Craigflower Manor National Historic Site (1853-6) in Victoria, BC is one of the oldest remaining farmhouse buildings in British Columbia and opened to the public in 1969. In January 2009, during an unusually cold winter, a fire started on the first floor. It was probably a “delayed ignition” (also called long term low temperature ignition) fire, caused by an electric heater warming and drying the area over time. There was no fire suppression in the house; fortunately, firefighters arrived in minutes, and extinguished the fire before it reached flashpoint.
Most of the damage was limited to the central staircase, adjacent to the ignition site. There was extensive charring of the structure and millwork, in some places total loss. There were also charred and blistered finishes and soot damage, but relatively little water damage. The restoration of Craigflower took four years, and along with cleaning included replacing wood elements (reusing the hardware as much as possible).
The worst damaged wood (judged as 50% or less of sound wood remaining) was removed. CO2 pellet blasting was used to remove char and soot from other areas, which worked well to quickly expose undamaged wood. Unfortunately, the plastic sheeting intended to contain all the material blasted off the surface was inadequate, and dust was deposited all throughout the house, requiring extensive cleanup in areas with no fire damage. While CO2 blasting companies will often claim that the process does not generate waste or leave behind residues, we should be aware that all the material blasted off during cleaning will go somewhere! Before using CO2 cleaning technique, test to determine how much dust will be generated, and make sure adequate extraction and abatement enclosures are in place before blasting. In the end, traditional mechanical removal of the char using chisels etc. may be more controllable and preferable.