Plasma cutting requires shaded filter lenses rated at a minimum of Shade 8 for most operations, with higher shades needed as amperage increases. The intense plasma arc produces ultraviolet and infrared radiation across a wide spectrum, from 200 to 1,400 nanometers, which can permanently damage your eyes in seconds without proper filtration.
Shade Numbers by Amperage
OSHA specifies minimum filter lens shade numbers for plasma arc cutting based on the amperage you’re running. These aren’t suggestions; they’re regulatory minimums.
- Light cutting (under 300 amps): Minimum Shade 8, with Shade 9 recommended for comfort
- Medium cutting (300 to 400 amps): Minimum Shade 9, with Shade 12 recommended for comfort
- Heavy cutting (400 to 800 amps): Minimum Shade 10, with Shade 14 recommended for comfort
Most hobbyists and small-shop operators run machines under 300 amps, so Shade 8 or 9 covers the majority of handheld plasma cutting work. The important caveat: these values apply when you can clearly see the arc. If the workpiece hides the arc from your line of sight, lighter filters can work. Many experienced operators use Shade 5 for light cutting tasks where the arc is obscured, though this provides less margin for error if the arc suddenly becomes visible as you reposition.
What the Plasma Arc Does to Unprotected Eyes
A plasma arc emits radiation across three ranges: ultraviolet (200 to 400 nm), visible light (400 to 700 nm), and infrared (700 to 1,400 nm). The UV radiation is the most immediately dangerous. It causes a condition commonly called “arc eye” or “welder’s flash,” which is inflammation of the membrane covering the front of your eye. Symptoms typically hit a few hours after exposure: intense pain, watering, gritty sensation, and light sensitivity. The infrared component penetrates deeper and can cause cumulative damage to the lens and retina over time, even without the dramatic pain of a UV flash burn.
This is why shade rating matters more than just wearing “something dark.” A pair of regular sunglasses blocks visible light but does almost nothing against the UV and IR wavelengths that cause the real damage. Proper filter lenses are designed to attenuate all three ranges simultaneously.
Auto-Darkening Helmets vs. Passive Lenses
You have two main options: a passive fixed-shade lens (in a helmet, goggles, or face shield) or an auto-darkening helmet that switches from a resting shade to a darker cutting shade when it detects the arc.
Auto-darkening helmets are popular because they let you see your cut line clearly before striking the arc, then darken automatically. Most auto-darkening helmets rest at Shade 3 or 4 in the “off” position and can be set to darken to your chosen shade. For plasma cutting, operators in the American Welding Society community commonly set their auto-darkening helmets to Shade 5 through 9, depending on amperage and personal comfort. Some use the helmet in its default resting shade (typically around Shade 5) for lighter plasma work, which still provides UV/IR filtration and full facial coverage.
Passive lenses are simpler, cheaper, and have no batteries to die mid-cut. The tradeoff is you can’t see your workpiece until the arc fires, which makes it harder to start a precise cut. For repetitive straight cuts on a table, this is less of an issue. For detailed freehand work, auto-darkening is noticeably easier to use.
If your auto-darkening helmet has a “cut mode” separate from its weld mode, use it. Cut mode typically offers lower shade ranges (Shade 5 to 8) better suited to the plasma arc’s brightness compared to the higher shades designed for welding.
Full Face Protection vs. Goggles and Glasses
Shade-rated safety glasses or goggles technically meet the filter lens requirement, but plasma cutting also throws molten metal, dross, and sparks. A full-face helmet or face shield with the correct shade filter protects your entire face from burns and spatter, not just your eyes from radiation. This is why most operators prefer a full welding helmet for plasma cutting rather than goggles alone.
If you do use safety glasses or goggles, make sure they carry the ANSI Z87.1+ rating, which means they’ve passed high-impact testing. The “+” indicates they can handle a projectile strike, not just basic pressure. Side shields are also required by OSHA when there’s a hazard from flying objects, and plasma cutting absolutely qualifies. Clip-on or slide-on side shields are acceptable if your glasses don’t have them built in.
The most thorough approach is layering: wear ANSI-rated safety glasses underneath a full-face shield or helmet. The face shield blocks the main spray of sparks and debris across your whole face, while the close-fitting glasses catch anything that slips around the edges of the shield. This dual setup is standard practice in grinding and applies equally to plasma cutting.
Choosing the Right Shade for Your Setup
The “right” shade is the one where you can comfortably see your cut line without squinting or straining, while still meeting the OSHA minimum for your amperage. If a Shade 8 lens leaves you seeing afterimages or feeling eye fatigue, step up to Shade 9 or 10. If Shade 9 makes everything too dark to follow your line accurately, you may be able to drop to Shade 8 if you’re under 300 amps.
A few practical guidelines worth noting. Thinner materials at lower amperages produce a less intense arc, so the lower shade range is usually fine. Thicker materials requiring higher amperages produce a brighter, more sustained arc that demands a darker filter. If you’re cutting overhead or in a position where the arc is directly in your field of vision with no workpiece blocking it, err toward the higher comfort shade rather than the bare minimum. And if bystanders or coworkers are nearby, they also need eye protection. Even peripheral exposure to the arc from across a shop can cause arc eye over repeated exposures.