Final answer:
Ultraviolet (UV) light is dangerous for welders as it cannot be felt, may penetrate clothing, and can cause harm to the eyes and skin. UV light carries more energy than visible light and can break bonds at the cellular level. It is mostly blocked by the ozone layer, but some rays from the Sun can still cause damage.
Step-by-step explanation:
Ultraviolet (UV) light is dangerous because the welder cannot feel it while being exposed to it, and it may pass through clothing. UV light carries more energy than visible light and can break bonds at the cellular level. High intensity UVB light can cause damage to the eyes and exposure can cause welder's flash (photo keratitis or arc eye) and may lead to cataracts and other medical issues.
UV light is mostly blocked by the ozone layer of Earth's atmosphere, but a small fraction of ultraviolet rays from the Sun do penetrate to cause sunburn or, in extreme cases of overexposure, skin cancer in human beings.
Ultraviolet light is sometimes called 'black light' because our eyes cannot see it. It is also used in special microscopes to detect details smaller than those observable with longer-wavelength visible-light microscopes.