The electric arc generated during welding is an extremely intense source of light and energy. This searing blue-white glow is a visible manifestation of plasma created by the ionization of gas between an electrode and the workpiece. While the visible light is intense enough to cause temporary blindness, the primary danger to an observer is the high-energy, non-visible components of the electromagnetic spectrum. Understanding these unseen forms of radiation is the first step in protecting the eyes, regardless of the distance from the operation.
The Invisible Hazard
A welding arc emits radiation across a broad range of wavelengths, including significant amounts of Ultraviolet (UV) radiation and Infrared (IR) radiation. Both UV and IR pose distinct threats to eye health. The UV component is particularly damaging and is categorized into UVA, UVB, and UVC radiation.
UVC radiation has the shortest wavelength and the highest energy, making it the most biologically harmful. While the atmosphere filters out natural UVC, a welding arc is an artificial source that produces UVC intensely. This radiation is almost entirely absorbed by the cornea, the clear outer layer of the eye. UVA and UVB rays are also generated, with UV-A passing through the cornea to be absorbed by the lens.
Infrared (IR) radiation is primarily felt as heat and is concentrated in the longer wavelengths of the arc’s output. IR radiation can heat the lens of the eye over time, and its harmful effects tend to be cumulative and chronic. Both UV and IR radiation can also reflect off surfaces like metal, concrete, and painted walls. This reflection creates an indirect exposure hazard for observers who may not even be looking directly at the arc.
The Role of Distance in Exposure
The intensity of light and radiation from any point source, including a welding arc, decreases rapidly with increasing distance. This is governed by the Inverse Square Law, meaning standing twice as far from the arc reduces the radiation exposure to one-fourth of the original intensity.
Despite this rapid fall-off, the sheer power of the arc means hazardous radiation never truly reaches zero at typical shop or construction site viewing distances. The dangerous range for UV exposure can extend up to 10–15 feet from the welding arc, depending on the welding type and amperage used. Some safety guidelines suggest a minimum safe viewing distance for an unshielded arc can be as far as 40 to 50 feet away.
Even a brief, accidental glance at a high-amperage arc from a moderate distance can deliver enough UV energy to cause an acute injury, known as flash burn. Repeated low-level exposure over time, even from a great distance or through reflected light, can also lead to long-term chronic damage. Therefore, relying on distance alone is an insufficient safeguard against the arc’s powerful, unseen radiation.
Types of Eye Damage from Arc Light
Acute Injuries
Exposure to the arc’s radiation can cause acute, immediate injuries. The most common acute injury is photokeratitis, also known as “arc eye” or “welder’s flash.” This condition is essentially a sunburn on the cornea and the conjunctiva, the mucous membrane covering the front of the eye.
Symptoms usually begin several hours after exposure, often waking the person at night. These symptoms include intense pain, a gritty sensation, excessive tearing, and abnormal sensitivity to light (photophobia). Although painful, arc eye is almost always temporary, with the surface layer of the eye healing itself within 24 to 48 hours.
Chronic Conditions
The more concerning issues are the chronic effects resulting from repeated low-level exposure over many years. Long-term exposure to UV radiation is strongly associated with the accelerated development of cataracts, which is a clouding of the eye’s lens. Infrared radiation can also contribute to this lens clouding by heating the eye tissue. Cumulative exposure to the high-energy blue-light component of the arc can potentially cause long-term damage to the retina.
Safe Viewing Practices for Observers
For individuals near the operation, simple precautions are necessary to mitigate the risk of exposure. The most effective method is to completely block the arc from view using physical barriers. Portable welding screens or opaque curtains should be used to shield the surrounding area and prevent direct or reflected exposure to bystanders.
Even when the arc is shielded, clear safety glasses should be worn, as they filter out a significant amount of UV radiation. Observers must make a conscious effort to turn their head or shield their eyes when the arc is struck. Minimizing peripheral vision exposure is important, as the eyes’ natural defense mechanisms are often too slow to prevent a damaging burst of intense light.