Laser Safety. Laser Sam's Laser Safety is a must read!
Laser Alignment Safety from LBL.
- 1 Eye Hazards
- 2 Electrical Hazards
- 2.1 How Much Current is Dangerous?
- 2.2 Types of Damage Caused by Electrical Hazards
- 2.3 Proper Procedures for Clearing High Voltage Circuits
- 2.4 Proper Procedures for Testing Live High Voltage Circuits
- 2.5 Laser Sam's Safety Tips for High Voltage Work
- 3 Causes of Laser Accidents
- 4 Laser Classes
- 5 Lasers and the FDA
Most importantly, any laser, even a 1/2 milliwatt laser pointer can be dangerous to The Eyes. Never point a laser directly in anyone's eye. Also it is very easy to catch a laser reflection off of something into your eye. Wear Laser protective glasses whenever possible and avoid directing the beam to any shiny surfaces.
When a laser beam reflects off a flat surface it becomes a spot that your eye must avoid. When it reflects of a cylindrical surface it becomes a line. While, it is a lower power density it is also large and harder to avoid. If you reflect off a spherical surface it becomes a very large object to avoid. Try, whenever posible, to make any mounts black and aim optics at the lowest power possible.
Higher power lasers (generally 5 Mw or more) should have a time delay connected to the ON switch. Often a key is required to prevent the high power laser from accidentally being activated.
When using high power lasers, turn the energy down as low as possible when aligning optics.
Eye Hazards for Pulsed Lasers
It is important to calculate the maximum power density of the object beam when making a pulsed portrait. Use large diffuser plates to enlarge the light source.
Here is some more information about The Eye.
Infra-Red Eye Hazards
Holographic lasers can be sources of 808nm light, 1064nm light in both continuous and pulsed modes. Most people can not detect any light at these frequencies. This makes verifying a non-function laser quite important. It is conceivable that light is emanating from a laser that appears dead.
The 532nm beam can be contaminated with IR light in some circumstances. Mirrors can be designed to reflect the 1064nm light and not the 532nm light (or visa versa). It is important to send any un-wanted IR light to a beam dump.
Flash Lamp Eye Hazzards
Flash Lamps can emit light from the UV to the Far IR. This light is very short but can cause considerable damage. Always shield flash lamps for testing. This helps protect from light and from lamp explosion. Do not operate flash lamps without a guard.
Quite a few laser use high voltage power supplies. Know your laser and it's power supply. Even some small HeNe lasers use high voltage capacitors that can discharge even when the laser is unplugged. Practice Safe Electrical Procedures.
Grounding is a very important aspect of safety in power supplies. Frayed cables, loose parts, motor or coil windings can be a source for an electrical fault. (metal etc becoming energized with voltage) With proper grounding this will cause a short as the ground takes the current back without much resistance which will trip a circuit breaker either in the unit or building.
Unfortunately, some buildings may not be wired correctly regarding ground safety or the wall outlet may not actually have a ground wire that runs back to the electrical circuit ground point and earth ground. Such ungrounded conditions will allow the voltage to remain present and if you become grounded by some condition and you become part of that path then you will take the current load.
Additionally high voltage (HV) used in the laser system also for the same reason should be grounded so that if a fault occurs it's current will induce a load that causes the power supply to disconnect via it's circuit breakers. It is the voltage difference that causes current to flow and you don't want to be in that path, so it's best to have the laser head hard grounded (at the same equip-potential) to the power supply and the power supply hard grounded to the building etc so that any faults trips breakers which prevent fires and hopefully electrocutions. Ground fault interrupters are better at breaking the current sooner since they operate at milliamp levels of current on the ground wire. More information about GFI at Sam's GFI
Always design circuits that have large capacitors so they automatically discharge if left unused.
A 1000V potential will easily jump 1cm. A 3000V potential will jump 3cm.
How Much Current is Dangerous?
- Electrical Current -- Biological Effect
- 1 mA threshold for feeling
- 10-20 mA voluntary let-go of circuit impossible
- 25 mA onset of muscular contractions
- 50-200 mA ventricular fibrillation or cardiac arrest
Types of Damage Caused by Electrical Hazards
Accidental contact with EXPOSED electrical parts operating at a VOLTAGE greater than 50 volts to ground, and having a current greater than 5 milliamperes, can cause serious injury or death. Fatal ventricular fibrillation of the heart can be triggered by a current flow of as little as several milliamperes. Severe injuries, such as deep internal burns, can occur even if the current does not pass through the vital organs or nerves.
Damage to the internal tissues may not be apparent immediately after contact with the current. Delayed internal tissue swelling and irritation are possible. Prompt medical attention can help minimize these effects and avoid death or long-term injury.
When an electric current passes through the air between two conductors, the temperature can reach 35,000°F. Exposure to these extreme temperatures can result in life threatening burns. The majority of hospital admissions due to electrical accidents are from arc-flash burns, not electrical shocks. Arc-flashes can and do kill at distances in excess of 10 ft.
The tremendous temperatures of the arc cause an explosive expansion of both metal and the surrounding air in the arc path. For example, copper expands by a factor of 67,000 times when changed from a solid into a vapor. The dangers of this explosion are of high blast pressure wave, high decibel levels of sound and high velocity shrapnel. Finally the material and molten metal is expelled away from the arc at speeds exceeding 700 miles per hour. Arc blasts often cause severe injuries and death.
Other burns suffered in electrical accidents are of two basic types: electrical burns and thermal contact burns. In electrical burns, tissue damage (whether skin deep or deeper) occurs because the body is unable to dissipate the heat caused by the current flow. Typically, electrical burns are slow to heal. Thermal contact burns are those normally experienced from skin contact with the hot surfaces of overheated electric conductors.
Proper Procedures for Clearing High Voltage Circuits
Proper Procedures for Testing Live High Voltage Circuits
Laser Sam's Safety Tips for High Voltage Work
- Author: Samuel M. Goldwasser
- Copyright (c) 1994, 1995, 1996, 1997, 1998 All Rights Reserved
Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:
- This notice is included in its entirety at the beginning.
- There is no charge except to cover the costs of copying.
The purpose of this set of guidelines is not to frighten you but rather to make you aware of the appropriate precautions. Repair of TVs, monitors, microwave ovens, and other consumer and industrial equipment can be both rewarding and economical. Just be sure that it is also safe!
- Don't work alone - in the event of an emergency another person's presence may be essential.
- Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system.
- Wear rubber bottom shoes or sneakers. An insulated floor is better than metal or bare concrete but this may be outside of your control. A rubber mat should be an acceptable substitute but a carpet, not matter how thick, may not be a particularly good insulator.
- Wear eye protection - large plastic lensed eyeglasses or safety goggles.
- Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts.
- Set up your work area away from possible grounds that you may accidentally contact.
- Have a fire extinguisher rated for electrical fires readily accessible in a location that won't get blocked should something burst into flames.
- Use a dust mask when cleaning inside electronic equipment and appliances, particularly TVs, monitors, vacuum cleaners, and other dust collectors.
- Know your equipment: TVs and monitors may use parts of the metal chassis as ground return yet the chassis may be electrically live with respect to the earth ground of the AC line. Microwave ovens use the chassis as ground return for the high voltage. In addition, do not assume that the chassis is a suitable ground for your test equipment!
- If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to. Hold them in place with string or electrical tape. Prop them up with insulation sticks - plastic or wood.
- If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a 2 W or greater resistor of 100 to 500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K to 100K ohm resistor). Monitor while discharging and/or verify that there is no residual charge with a suitable voltmeter. In a TV or monitor, if you are removing the high voltage connection to the CRT (to replace the flyback transformer for example) first discharge the CRT contact (under the insulating cup at the end of the fat red wire). Use a 1M to 10M ohm 1W or greater wattage resistor on the end of an insulating stick or the probe of a high voltage meter. Discharge to the metal frame which is connected to the outside of the CRT.
- For TVs and monitors in particular, there is the additional danger of CRT implosion - take care not to bang the CRT envelope with your tools. An implosion will scatter shards of glass at high velocity in every direction. There is several tons of force attempting to crush the typical CRT. Always wear eye protection. While the actual chance of a violent implosion is relatively small, why take chances? (However, breaking the relatively fragile neck off the CRT WILL be embarrassing at the very least.)
- Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations.
- If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand.
- Perform as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in the power supply section of a TV or monitor can be tested for short circuits with an ohmmeter.
- Use an isolation transformer if there is any chance of contacting line connected circuits. A Variac(tm) (variable autotransformer) is not an isolation transformer! However, the combination of a Variac and isolation transformer maintains the safety benefits and is a very versatile device. See the document "Repair Briefs, An Introduction", available at this site, for more details.
- The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but may not protect you from shock from many points in a line connected TV or monitor, or the high voltage side of a microwave oven, for example. (Note however, that, a GFCI may nuisance trip at power-on or at other random times due to leakage paths (like your scope probe ground) or the highly capacitive or inductive input characteristics of line powered equipment.) A GFCI is also a relatively complex active device which may not be designed for repeated tripping - you are depending on some action to be taken (and bad things happen if it doesn't!) - unlike the passive nature of an isolation transformer. A fuse or circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment. However, these devices may save your scope probe ground wire should you accidentally connect it to a live chassis.
- When handling static sensitive components, an anti-static wrist strap is recommended. However, it should be constructed of high resistance materials with a high resistance path between you and the chassis (greater than 100K ohms). Never use metallic conductors as you would then become an excellent path to ground for line current or risk amputating your hand at the wrist when you accidentally contacted that 1000 A welder supply!
- Don't attempt repair work when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity.
- Finally, never assume anything without checking it out for yourself! Don't take shortcuts!
Causes of Laser Accidents
Some Common Causes of Laser Accidents from LBL.
- Not wearing protective eyewear during alignment procedures
- Not wearing protective eyewear in the laser control area
- Misaligned optics and upwardly directed beams
- Equipment malfunction
- Improper methods of handling high voltage
- Available eye protection not used
- Intentional exposure of unprotected personnel
- Lack of protection from nonbeam hazards
- Failure to follow the AHD
- Bypassing of interlocks, door, and laser housing
- Insertion of reflective materials into beam paths
- Lack of preplanning
- Turning on power supply accidentally
- Operating unfamiliar equipment
- Wearing the wrong eyewear
Laser usually contained within the product and considered non- hazardous. Laers are less than .4 mw and require no labeling.
Laser printers, CD players, DVD players
Visible laser or laser system that cannot cause eye damage unless viewed directly for an extended period of time, or with magnifiers, binoculars, or telescopes. Laser power .4 mw to 1mw.
Bar code scanners
Laser Power is less than 1mw. Labled: Caution - Do not stare into beam.
Laser that normally does not present a risk of injury if viewed momentarily with an unaided eye, but may present a greater risk if viewed using magnifiers, binoculars, or telescopes.
Laser Power < 5 mw. Labled:CAUTION - Laser Radiation - Do Not Stare into Beam or View Directly with Optical Instruments.
Laser can cause eye damage if viewed directly.
Laser power < 500 mw. Labled: DANGER - Laser Radiation - Avoid Direct Exposure to Beam
Laser light shows, Industrial lasers, Research lasers.
Laser may cause severe eye injury with short duration exposure to the direct or reflected beam. May also cause severe skin damage and present a fire hazard.
Laser Power: > 500 mw. Labled - DANGER - Laser Radiation - Avoid Eye or Skin Exposure to Beam.
Laser light shows, Industrial lasers, Research lasers
Lasers and the FDA
All laser devices distributed for both human and animal treatment in the U.S. are subject to Mandatory Performance Standards. They must meet the Federal laser product performance standard and must submit an "initial report" to CDRH's Office of Compliance prior to distributing the product (see 21 CFR 1000-1040.11). This performance standard specifies the safety features and labeling that all laser products must have in order to provide adequate safety to users and patients. A laser product manufacturer must certify that each model complies with the standard before introducing the laser into U.S. commerce. This includes distribution for use during clinical investigations prior to device approval.
Certification of a laser product means that each unit has passed a quality assurance test and that it complies with the performance standard. The firm that certifies a laser product assumes responsibility for product reporting, recordkeeping, and notification of defects, noncompliances, and accidental radiation occurrences, as specified in sections 21 CFR 1000-1010. A certifier of a laser product is required to report the product via a Laser Product Report submitted to CDRH. Reporting guides and related regulatory information are available from the DSMA web site at: http://www.fda.gov/cdrh/devadvice. Distribution of any certified laser products internationally would also require submission of the report.
The FDA has the authority to regulate all kinds of lasers. Under the Medical Device Amendments to the Federal Food, Drug, and Cosmetic Act, the agency regulates lasers used in medicine. And under the Electronic Product Radiation Control Provisions of the act, the FDA regulates both medical and nonmedical lasers such as those used to solder circuits in factories, to scan groceries in a supermarket, or to entertain a crowd with a light show in the night sky.
The FDA may inspect manufacturers of laser products and require the recall of products that don't comply with federal standards or that have radiation safety defects. The agency also may test laser products and inspect displays of laser light shows to ensure the public is protected. Producers of laser light shows are required to tell the FDA where they are planning a display so that the agency can inspect it if possible and take action if required. In 1995, the FDA, working with the Federal Aviation Administration, issued a moratorium that remains in effect on outdoor laser light shows in and near Las Vegas. The action, which affects Clark County, Nev., was taken after airline pilots reported experiencing temporary visual impairment during flights into or out of the county's three airports.
The FDA requires that labeling on most laser products contain a warning about radiation and other hazards and a statement certifying that the laser complies with FDA safety regulations. The label must also state the power output and the hazard class of the product.
The FDA recognizes four major hazard classes (I to IV), including two subclasses (IIIa and IIIb), of lasers--ranging from those that pose no known hazard to those that pose serious danger if used improperly. The higher the class, the more powerful the laser. Class I laser products, for example, include laser printers and CD players, which are not considered hazardous because the laser radiation is contained within the product.
Class IIIb and class IV laser products are very powerful and permit ready access to the laser radiation, which can cause eye or skin injury. Research and industrial lasers and laser light show projectors fall into these classes. Class IIIb and class IV laser light show projectors may be sold only by or to individuals or firms that have obtained approval from the FDA.