Heavy Ignition Source : Objects that will tend to settle or burrow under the surface of the materials first ignited as a result of either weight or temperature. I.e., welding slag, exhaust particles, large metal fragments, etc.
National Wildfire Coordinating Group (NWCG), Glossary of Wildland Fire Terminology, NWCG Program Management Unit, National Interagency Fire Center, Boise, ID, USA 2014. http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf, (For Fr - Amer) {45}