WHAT IS A CLASS 4 LASER?
Class 4 lasers are hazardous for eye exposure. They also can burn skin and materials, especially dark and/or lightweight materials at close range. They should be used with extreme care. For visible-light lasers, Class 4 lasers’ have an output power 500 milliwatts and above. There is no upper limit for Class 4 — this is the most hazardous laser classification. Class 4 is the same as the Roman numeral “Class IV” you may see on some lasers’ labels.
A class 4 laser pointer beam can cause materials to smolder or burn, especially at close range. Keep the beam moving to avoid burning materials at close range. Dark materials which absorb heat, and lightweight materials such as paper and fabric, are most easily burned by visible laser beams. Laser glasses or goggles should be used when working with Class IV lasers, especially at close range. They should be selected to protect against the laser’s power and wavelength.
SAFE USE GUIDANCE – GENERAL
Class IV visible-beam lasers are high-powered. A Class 4 laser can cause a significant eye injury if the beam, whether direct or reflected, enters the eye. Even staring at the diffuse reflection of a laser “dot” on a wall or other surface, may cause an eye injury within a few feet of the dot. Do not stare at the laser “dot” when it is close to you.
To prevent eye exposure, always be aware of the beam location. Keep it away from people’s eyes and heads. Watch out for reflected beams from glass and shiny surfaces. Use of laser protective eyewear is recommended, as discussed elsewhere on this page.
AVOID SKIN EXPOSURE
Avoid exposure to skin and sensitive materials. A Class iv laser can burn skin and materials, especially dark and/or lightweight materials at close range.
DO NOT AIM AT AIRCRAFT OR VEHICLES
A Class 4 laser can be a distraction, glare or flashblindness hazard for pilots and drivers. It may also be a potential eye injury hazard for pilots at relatively close range. NEVER aim any laser towards an aircraft or moving vehicle.
ONLY ALLOW USE BY RESPONSIBLE PERSONS
This is not a toy. Children should never be permitted to use Class 4 lasers. Any teenager using a Class IV laser pointers should be continuously supervised by a responsible adult. A number of teenagers have caused eye injuries to themselves or others by misusing Class 3B and Class 4 lasers.
DO NOT USE AS A LASER POINTER
Even if this laser looks like a pointer or flashlight, do not use this laser for pointing purposes. Class 4 lasers are too powerful to be used as pointers. Use a Class 2 (less than 1 mW) or Class 3A (less than 5 mW) laser for pointing purposes.
EYE INJURY HAZARDS
Class 4 visible-light lasers are significantly hazardous for eye exposure. They can cause burns to the retina. A person cannot turn away or blink fast enough to prevent retinal eye injury from a Class IV laser. Prevent all eye exposure to beams from Class iv lasers. This includes accidental exposures — be careful to keep the beam away from eyes and faces.
Also, remember that reflections off mirrors, glass, and shiny surfaces can be just as hazardous as the direct beam. Avoid reflected Class 4 beams the same way you would avoid the direct beam. If this is not listed, here are some example Class 4 lasers:
The Nominal Ocular Hazard Distance (NOHD) for a 1000 milliwatt (1 Watt) visible-beam laser with 1 milliradian divergence is 740 ft (225 m). The NOHD for a 5 Watt laser with a 1 milliradian divergence is 1640 ft (500 m). Additional types of Class 4 lasers are listed in the Laser hazard distance chart. You can also use the online laser hazard distance calculator to precisely determine the NOHD and visual interference distances of this laser.
If you are closer than the NOHD distance to the blue laser, there is a possibility of retinal damage if the direct or reflected beam enters your eye. The closer you are to the laser and the longer the beam is in the eye, the greater the chance of injury.
The scattered light from the laser “dot” as viewed on a surface, can be an eye hazard. Avoid looking directly at the laser dot for more than a few seconds. The light is too bright if you see a sustained afterimage, lasting more than about 10 seconds. The more powerful laser, and the closer your eye is to the laser dot, the greater the chance of injury. This can occur during certain actions, such as aligning the beam or trying to hold the laser dot on a fixed location in order to burn a material.
Looking at the laser dot from a 1,000 milliwatt (1 Watt) Class 4 blue (445 nm) laser beam for more than 1 minute is an eye hazard within 1.5 ft (44 cm) of the laser. Looking at the laser dot from a 10,000 milliwatt (10 Watt) Class 4 blue (445 nm) laser beam for more than 1 minute is an eye hazard within 4.5 ft (1.4 m) of the laser. Even just for 10 seconds, viewing the laser dot is a hazard within 1.8 ft (0.6 m).
If you must look at the laser dot for relatively long periods of time within the hazard distances, use laser protective eyewear.
SKIN INJURY (BURN) HAZARD
A Class 4 laser beam can burn skin and some materials. The more powerful laser, the faster the burn will occur. In some cases, the burn may be almost instantaneous. A 1000 milliwatt (1 Watt) Class 4 laser beam is a skin injury hazard within 39 in (1 meter) of the laser. Avoid skin exposure to a Class iv laser beam, especially at close range. A skin burn can be very painful, can take long to heal, and can leave a permanent scar.
MATERIALS DAMAGE AND BURNING
A Class IV laser beam can cause materials to smolder or burn, especially at close range. Keep the beam moving to avoid burning materials at close range. Dark materials which absorb heat, and lightweight materials such as paper and fabric, are most easily burned by visible laser beams. A 1000 milliwatt (1 Watt) Class 4 laser beam is considered a burn hazard within 26 inches (67 cm) of the laser.
AIRCRAFT AND VEHICLE SAFETY
NEVER aim any laser towards an aircraft or vehicle that is in motion. The bright light can flashblind, cause glare, or distract the pilot or driver.
A 1000 mW (1 Watt) Class 4 laser beam can temporarily flashblind a pilot or driver, causing afterimages, within 0.7 miles (1.1 km) of the laser. It can cause glare, blocking a pilot or driver’s vision, within 3.1 miles (5 km) of the laser. It can cause distraction, being brighter than surrounding lights, within 31 miles (50 km) of the laser.
The above calculations are for a 555 nanometer green laser pointers with 1 milliradian divergence. These parameters are very conservative and thus result in the longest visual interference distances for a 1 Watt consumer laser. The more the beam spreads out, the shorter the hazard distances. For example, for a 1 Watt 555 nm green laser pointer with a beam spread of 2 milliradians, divide the above numbers by 2 to find the visual interference distances.
Green is the most visible color to the human eye. It will appear brighter and more distracting than other colors of equal power. For red, divide the above numbers by about 5 to get an approximation of the visual interference distances. For blue, divide the above numbers by about 20.