Final answer:
A welder utilizes an electric arc to produce the necessary heat for welding metals. The right answer to the fill-in-the-blank question is 'Arc', as flames, sparks, and lasers are not the methods utilized in this context for welding. Welding electric arcs emit intense heat and light, requiring proper safety gear.
Step-by-step explanation:
A welder uses a high electric current to create an electric arc that produces heat for joining metal. This process is not achieved through a flame, spark, or laser, but specifically through the formation of an arc. An electric arc is a discharge of electricity through a gas that is ionized by the high temperature created between two electrodes. The intense heat from the arc melts the metals to be joined, allowing them to fuse when they cool.
Welders must wear protective gloves and helmets to safeguard themselves from the hazards of the electric arc, such as thermal energy, high-energy electromagnetic radiation, and sparks, which can spray and cause burns or even damage the retina if eyes are left unprotected. The light emitted by the arc is so intense that it can be seen for kilometers, and the thermal energy can be felt several meters away.