What shade lens is required during the ignition and pouring of molten steel?

During the ignition and pouring of molten steel in thermite welding, a lens that is shade 5 is required to protect the welder's eyes. The intense light and infrared radiation emitted during the thermite reaction can be damaging to the eyes. A shade 5 lens strikes a balance, providing adequate protection against the bright light generated while not being too dark, which could impair visibility when monitoring the process.

Choosing the appropriate lens shade is critical to ensure both safety and visibility. A shade that is too light would not block enough of the harmful radiation, while a shade that is too dark could hinder the ability to see the critical aspects of the welding operation. Thus, a shade 5 lens provides an optimal level of protection for these specific conditions.