Dressed for the Arc
The arc's light is intense enough to injure eyes and skin in seconds, so a shade lens, safety glasses, gloves, and flame-resistant cover are the first step of every weld. · 9 min
A welding arc is the brightest thing most people will ever stand near. It is not only bright to look at: the same light carries ultraviolet and infrared energy strong enough to injure eyes and skin in seconds. That sounds like a reason to fear the work. It is actually a reason to dress for it. Every hazard in this folio has a piece of gear that answers it, and dressing correctly takes about ninety seconds once it is habit.
Guess before you learn
Across the shop, another welder strikes an arc and you watch it, bare-eyed, for two or three seconds. What happens to your eyes?
Ultraviolet light can burn the cornea — the clear front window of the eye — in seconds, even at a distance and even off a reflection. The injury, called arc eye, announces itself three to twelve hours later: a gritty, light-sensitive soreness that welders describe as sand under the eyelids. It usually heals in a day or two, and it is entirely preventable. Prevention is this folio.
9–12
3–5
Sunlight can burn your skin at the beach — that is ultraviolet light at work. A welding arc pours out the same kind of light, but far stronger, from an arm's length away. It can redden skin and sore up eyes in seconds instead of hours.
The answer is simple gear worn every single time: a helmet with a dark filter window for the eyes, safety glasses underneath it, leather gloves for the hands, and a jacket with the sleeves rolled down. Dressed like that, a welder can watch the arc all day.
6–8
The arc gives off three kinds of light at once: visible light (the blinding glare), ultraviolet (the burning kind, the same energy behind sunburn), and infrared (felt as heat). Ultraviolet is the sneaky one. It burns the cornea — the eye's clear front surface — without any warning pain. The burn, called arc eye, shows up three to twelve hours later; welders describe it as sand under the eyelids.
Each piece of gear answers one part of the hazard. The helmet's shade lens absorbs nearly all of the arc's light, leaving a safe, dim picture of the puddle. Safety glasses underneath catch flying chips when the hood is up. Leather gloves and a buttoned, flame-resistant jacket keep ultraviolet and sparks off your skin — a bare forearm can redden in minutes of arc time.
9–12
Arc radiation spans infrared, visible, and ultraviolet. The ultraviolet band does the damage: the cornea absorbs it strongly, and the absorbed dose injures surface cells that die and slough off hours later — that delay is why arc eye never hurts at the moment of exposure. Skin receives the same dose, which is why welders sunburn through an afternoon of short beads if their sleeves are up.
Intensity falls with the square of distance, so a glance across the shop is milder than a glance at your own arc — but reflections off bare walls and shiny plate carry ultraviolet around corners, so gear stays on for bystanders too. The shade lens is a calibrated filter: shade 10 passes roughly a hundredth of one percent of the arc's visible light, and even less of its ultraviolet.
K–2
A welding arc is a very, very bright light. Looking at it can hurt your eyes, the way staring at the sun can. Welders never look at it with bare eyes.
So welders wear a helmet with a special dark window. The dark window lets them watch the melting metal safely. Thick gloves and long sleeves keep the bright light off their skin.
Undergrad
Arc emission is broadband: a quasi-blackbody continuum from a column near 6,000 K plus line emission from metal vapor. The actinic band — UV-B and UV-C, roughly 180 to 315 nm — drives photokeratitis: the corneal epithelium absorbs strongly below 315 nm and accumulates an injurious dose within seconds at working distance. Note that the sun delivers no UV-C at ground level; the ozone layer absorbs it. A welding arc delivers it from two feet away.
Protection standards quantify all of this. ANSI Z49.1 tabulates minimum and suggested shade numbers by process and arc current, and filter shades are logarithmic — each step multiplies the attenuation. Flame-resistant clothing closes the loop, because ordinary synthetics both pass ultraviolet and melt onto skin when spatter lands. Cotton chars; polyester becomes part of the burn.
Postgrad
Filter shade S and optical density are linked by S = (7/3)·OD + 1, so shade 10 corresponds to OD near 3.9 — visible transmittance on the order of one ten-thousandth — with parallel requirements on ultraviolet and infrared attenuation that hold whether or not an auto-darkening cartridge has fired: the UV/IR blocking is a static interference coating, and the liquid-crystal shutter modulates only visible light. A failed auto-darkening lens therefore startles but does not burn.
Exposure limits derive from threshold limit values for actinic ultraviolet — an eight-hour effective radiant exposure of 3 mJ/cm² — against which the measured irradiance of a 150 A arc at half a meter implies a permissible bare-eye exposure well under one second. The margin is too thin for administrative controls: only the physical filter is reliable, and habit, not signage, is the actual curriculum.
arc eye
Photokeratitis — a burn of the cornea from the arc's ultraviolet light. Painless at exposure, gritty and light-sensitive three to twelve hours later, healed in a day or two. Fully preventable with a shade lens.
How dark is dark enough? Filter lenses are numbered — the shade number — and higher numbers pass less light. The right shade depends on how bright the arc is, which mostly follows amperage: more current, more light. Before you see the published table, commit your instinct to pencil below.
Why is this true?
Why is the rule "start too dark, then lighten" instead of the reverse?
Because the two errors are not symmetric. A lens one shade too dark costs you a clear view for a moment; a lens too light costs your corneas a dose you cannot feel until tonight. You can always recover from dim.
Eyes settled, the rest is skin. Ultraviolet burns forearms through a thin summer shirt; sparks land and roll, and synthetic fabric melts where they land. So the cover is specific: leather gloves, a flame-resistant jacket with collar and cuffs closed, cuffless pants over leather boots — sparks find open cuffs and pockets with remarkable reliability — and no frayed edges anywhere. Cotton chars; polyester melts into the burn. Dress-out has a fixed order, because a fixed order is what turns gear into habit rather than a checklist:
Choose the lens for a 90 A job — the steps fade as you master them
90 A falls in the 60–160 A band
Suggested shade: 10
Darker (11) is fine if glare bothers you; lighter than the minimum (8) never is
That is the whole outfit and the reasoning behind it: the arc emits light strong enough to injure in seconds, and every piece of gear intercepts a specific part of that light or the sparks that travel with it. Next folio: the hazards you cannot see at all — fume in the air you breathe, and fire that waits until you leave.
Note
Auto-darkening or fixed-shade lens is a preference; the shade number is not. Whichever helmet you buy, check that the number on the cartridge matches the amperage you run.
Practice — new ink and old, interleaved
1.Which statement about arc eye is accurate?
2.Put the dress-out sequence in its taught order.
- Flame-resistant jacket on, collar and cuffs closed
- Safety glasses on
- Leather gloves on
- Helmet on, hood dropped last before the arc
3.Stick welding at 120 A — what suggested shade number?
4.Why does the gear stay on even when you are only watching someone else weld?
The arc's ultraviolet injures at a distance and off reflections, so a bystander's eyes and skin need the same protection as the welder's.
How close were you? Grade yourself honestly — it sets your review date.