For most plasma cutting, you need a shade 8 to 10 lens, depending on the amperage of your machine. Light plasma cutting below 300 amps calls for a minimum shade 8, medium cutting between 300 and 400 amps requires shade 9, and heavy cutting from 400 to 800 amps requires shade 10. These minimums come directly from OSHA’s filter lens table under regulation 1910.133.
Shade Numbers by Amperage
The shade number you need scales with how much current your plasma cutter draws. Higher amperage means a brighter, more intense arc, which demands a darker lens. Here’s the breakdown:
- Below 300 amps: Shade 8 minimum
- 300 to 400 amps: Shade 9 minimum
- 400 to 800 amps: Shade 10 minimum
These are minimum values. OSHA’s own guidance suggests starting with a shade that’s too dark to see the cut zone, then stepping down to a lighter shade until you get a clear view of the work, without dropping below the listed minimum. If you’re comfortable working with shade 9 on a 200-amp machine even though shade 8 is the floor, that’s perfectly fine. Darker is always safer for your eyes.
Low-Amperage Handheld Cutters
Most hobbyists and small-shop fabricators use handheld plasma cutters in the 20 to 60 amp range, well under the 300-amp threshold. Shade 8 is the official minimum for this entire “light” category. Some lens guides suggest that shades as low as 5 can work for very low-current plasma cutting on thin material, but shade 8 remains the OSHA baseline for plasma arc cutting regardless of how small the machine is.
There’s a practical exception worth knowing: when the arc is hidden behind the workpiece and you can’t directly see it, lighter shades are acceptable. This comes up with CNC plasma tables where the operator stands back from the cut and the torch is partially shielded by the material. If you’re hand-cutting and looking directly at the arc, stick with shade 8 or higher.
Why Plasma Arcs Are Harder on Your Eyes Than You’d Expect
A plasma arc produces dangerous levels of ultraviolet-B, ultraviolet-C, and visible light radiation. A NIOSH evaluation of a steel building materials manufacturer measured optical radiation at various distances and amperages during plasma cutting and found that UV-B, UV-C, and visible light levels all exceeded safe exposure limits for unprotected eyes. Interestingly, infrared and UV-A radiation stayed near background levels, meaning the primary threat isn’t heat radiation but the shorter-wavelength UV that causes immediate damage to the surface of the eye.
Unprotected exposure to UV-B and UV-C from a plasma arc can cause photokeratitis, sometimes called “arc eye” or “welder’s flash.” It feels like sand in your eyes, typically hitting several hours after exposure. Repeated exposure over time raises the risk of cataracts. Even brief glances at an unshielded plasma arc without proper filtration can cause damage, which is why bystanders in the shop need protection too, not just the operator.
What Type of Eye Protection to Use
A full-face welding helmet with the correct shade lens gives you the best protection for plasma cutting. It shields your eyes from optical radiation and protects the skin on your face from UV burns. NIOSH investigators specifically recommended shades that cover the operator’s full face, not just safety glasses with tinted lenses.
Auto-darkening helmets work well for plasma cutting as long as they cover the shade range you need. Most auto-darkening helmets adjust from about shade 9 to 13, which handles medium and heavy plasma cutting. Some models go down to shade 5 in their cutting mode, which may be useful for visibility but sits below the shade 8 minimum for plasma arcs. Check that your helmet’s low setting doesn’t drop below 8 when using it for plasma work.
All eye and face protection used in the workplace must comply with ANSI Z87.1 standards. Look for the Z87 marking on the lens or frame to confirm it meets impact and optical requirements on top of providing the correct shade.
Protecting Others in the Work Area
The NIOSH evaluation also recommended enclosing the plasma arc area with welding curtains, posting optical radiation warning signs, and installing audible or visual alerts when the plasma cutter is operating. If you’re cutting in a shared shop, anyone within line of sight of the arc needs shaded eye protection or a physical barrier between them and the light source. Standard safety glasses without shading won’t block the UV-C and UV-B wavelengths that plasma arcs produce at hazardous levels.