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Laser and smoke generator

Flow visualization uses a small green laser to illuminate a sheet of glycol smoke. Both components are low-hazard for trained operators but can cause real injuries when mishandled — eye damage from beam mis-alignment, respiratory irritation from over-fogged enclosed spaces.

Laser

Current installation: a 5 mW Class 2 laser, powered from a DC bench supply preset to 12 V, with a glass rod placed in front of the beam to spread it into a sheet for slicing the smoke (see Hardware → Laser & smoke generator for photos).

Hazard class

Class 2 (visible, < 1 mW continuous wave per ANSI Z136.1) is considered eye-safe via the blink reflex at the cornea: looking directly into the beam for less than 0.25 s does not damage the retina. The 5 mW device in this lab is at the upper end of Class 2 (some references classify it as 3R); treat it conservatively.

Rules

  1. No staring into the beam, even briefly. Blink reflex assumes an involuntary blink within 0.25 s; intentional staring overrides it.
  2. No reflective objects in the beam path. Watches, jewellery, polished metal — remove or cover. The beam reflects off curved surfaces at angles that can find an eye.
  3. The beam must terminate on a diffuse, non-reflective surface. Black-anodized aluminium or matte black painted card, not bare metal or glossy plastic.
  4. Door placard updated when the laser is in use: "Laser in use — Class 2, do not enter without authorization."
  5. Eyewear is not strictly required for Class 2 but is recommended during alignment. UCI EH&S can advise on appropriate optical density if alignment becomes a frequent activity.
  6. Power supply 12 V exactly — do not raise the voltage. Higher voltage will raise the optical power output past Class 2.

Current known issue

The glass-rod sheet former produces a sheet with intensity concentrated at the centre rather than uniform across the sheet. This is the subject of the Project improvements thread. For now, position the test article within the centre of the sheet where intensity is highest, and do not expect quantitative streamline analysis from the current optics.

Reference

Smoke generator

Current installation: small commercial smoke generator with wired remote placed at the computer station; generator itself sits near the tunnel inlet. Current settings are recorded in the Hardware → Laser & smoke generator photo.

Hazard

Glycol smoke is low-toxicity but respiratory-irritating in enclosed spaces. Symptoms of overexposure are coughing, eye irritation, and shortness of breath. The smoke generator vents into the tunnel inlet and is carried through the test section to the exhaust path, so the operator is usually downstream of the smoke — but a stalled tunnel or a back-eddy can put smoke into the operator's breathing space.

Rules

  1. The tunnel must be running before the smoke generator is enabled. Smoke is meant to be entrained by airflow; without airflow it pools in the room.
  2. Stop the smoke generator before stopping the tunnel. Order of shutdown: smoke off → wait for the test section to clear → tunnel off. See Operations → Shutdown.
  3. Stop the run immediately if anyone reports respiratory irritation or eye irritation. Open the lab door for ventilation. UCI EH&S "Who Do I Call?" odor / irritation contact: safety@uci.edu, 949-824-6200.
  4. No smoke generator while the door placard does not warn of fog. Class 2 laser plus smoke can trip a fire alarm if a stray detector is in the airflow path; coordinate with building management if you're not sure.
  5. Refill the glycol reservoir in the off state with the unit unplugged. Spills onto the heater element are an electrical hazard and a smoke-quality hazard (uneven dispersion next run).

Optimizing settings

Smoke density, particle size, and dispersion stability depend on the generator's settings (heater temperature, fluid flow rate, fan speed) and on the ambient tunnel airflow. The current settings (photographed) are a starting point, not a calibrated optimum. The Project improvements thread plans an empirical sweep.

Door placard policy

The lab door placard must reflect the currently active hazards. When the laser or smoke generator is in use, the placard must show:

  • the laser pictogram and "Class 2 in use" annotation;
  • the smoke / fog warning;
  • the PI name and emergency contacts;
  • the date of last chemical inventory.

UCI placard policy and the generator app are at https://www.ehs.uci.edu/research-safety/lab-safety-inspections/labels-signs.php. The full reference guide is the Laboratory Door Placards Reference Guide (PDF).