UV Curing calculator

UV Safety Exposure Calculator

ACGIH publishes a Threshold Limit Value (TLV) for UV exposure of 3.0 mJ/cm² of effective UV-actinic over an 8-hour day at the operator. Stray UV from cure cells (open belts, side-fire heads, missing guards) can exceed that quickly. This calculator combines the TLV, the irradiance you measured at the operator position, and a safety multiplier (4× is industrial-hygiene standard) to get the maximum permissible exposure time before PPE or guarding becomes mandatory.

What this calculator does

  • Calculate the maximum permissible operator exposure time before reaching the ACGIH TLV given a measured ambient UV irradiance and the band-specific exposure limit.
  • Use it on safety walkthroughs and PPE decisions when stray UV from cure cells reaches operator areas — to prove you're under the threshold limit value or to size a guard.
  • Returns the seconds an operator can stand in a stray-UV field before hitting the ACGIH TLV, with the industrial-hygiene safety multiplier applied.

Formula used

  • Base exposure (sec) = exposure limit (mJ/cm²) ÷ measured irradiance (mW/cm²)
  • Permissible exposure = base exposure ÷ (1 + safety multiplier)

Inputs explained

  • Exposure limit (effective dose): ACGIH effective TLV for UV-actinic = 3.0 mJ/cm²/day at the operator; check band-specific limits for UV-A / IR.
  • Measured ambient irradiance at operator: Calibrated radiometer reading at head/eye height where the operator stands.
  • Safety factor: Pulls the limit down for measurement uncertainty and posture variability; 4× = enter 300%.

How to use the result

  • Use it on safety walkthroughs (especially after a guard is opened for cleaning), during PPE decisions, when investigating reports of skin or eye irritation, and as part of a UV safety job hazard analysis.
  • TLV math is wavelength-band sensitive. The 3.0 mJ/cm² number is the simple effective UV-actinic TLV; UV-A has a separate 1 J/cm² limit for the eye. For a defensible compliance number, use a radiometer that reports band-weighted effective irradiance, not raw broadband.

Common questions

  • What does the TLV protect against? Photokeratitis (welder's eye / arc eye) and erythema (UV burn / sunburn) from acute exposure to UV-B and UV-C, plus longer-term cataract and skin cancer risk. The 3 mJ/cm² day limit is sized to keep all three risks at acceptable levels for a working lifetime.
  • What if my permissible exposure is just a few seconds? You have a guarding problem, not a procedural one. A few-second TLV at the operator means stray UV is too high for any realistic work pattern. Add interlock-protected guards, side curtains, or a tunnel enclosure — not PPE alone. PPE protects skin and eyes during incidental exposure; it doesn't substitute for engineering controls.
  • What PPE is appropriate? UV-rated face shield (not standard safety glasses — most clear safety glass passes UV-A), long sleeves in UV-blocking fabric, gloves at any reach-in point. Eye PPE should be marked for the relevant UV band. Don't substitute welding shade for UV — different filter chemistry.
  • Why a 4× safety multiplier? Industrial-hygiene practice — accounts for measurement uncertainty (often ±20%), operator posture (a 6'2" operator's eye level is different from a 5'4" operator's), and exposure-time uncertainty (operators rarely stand for exactly the planned time). 4× is the conventional default; some plants use 2× with documented reasoning.

Last reviewed 2026-05-12.