Welding in Paris is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. Welding can be done in open air, under water and in outer space. Regardless of location, it remains dangerous, and precautions are taken to avoid burns, electric shock, eye damage, poisonous fumes, and over exposure to ultraviolet light.