For certain contracts the Navy requires parts to be certified as Mercury Free - The Navy states that material supplied under this contract/purchase order is intended for use on submarines/surface ships and therefore shall contain no metallic mercury and shall be free from mercury contamination. Mercury contamination of the material will be cause for rejection. If the inclusion of metallic mercury is required as a functional part of the material furnished under this contract. The Contractor shall obtain written approval from the Procurement Contracting Officer before proceeding with manufacture. The contractor's request shall explain in detail the requirements for mercury. Identify specifically the parts to contain mercury. and explain the method of protection against mercury escape. Such a request will be forwarded directly to the Procurement Contracting Officer with a copy to the applicable Government Inspector. Upon approval by the Contracting Officer. the vendor will provide a "Warning Plate" stating that metallic mercury is a functional part of the item and will include name and location of that part.