This notice is being published to inform the regulated community of how PHMSA has previously reviewed and classified certain thermite formulations and how it has temporarily reclassified certain thermite formulations as Division 4.1 flammable solids instead of Class 1 explosives while PHMSA completes its ongoing research project on thermite formulation classification. The notice also explains how PHMSA is instructing its approved test labs to evaluate thermite formulations submitted for classification testing.  See the notice for full details.