There are various types of laboratory furnaces, including Tube, Box, and Muffle. Because each unit is different, read the manual, complete safety training provided by your PI or trained senior colleagues. Only use a furnace that you fully understand how to operate. Furnaces present electrical, fire, and burn hazards, and the insulation can pose a health hazard. Furnaces can also create inhalation health hazards if they malfunction and are not stored in appropriate containment, like a fume hood. Regularly inspect your furnace for any loose or damaged wiring, physical defects, and water or heat damage. Follow the safety guidelines outlined in the linked document above, and contact the manufacturer if you have questions regarding specific use or servicing of your furnace.