Laser control measures

The hierarchy of control for selecting appropriate control measures for laser safety is:

1. Engineering controls
2. Administrative controls
3. Personal protective equipment

Even then there is a hierarchy within each type of control and in practical terms, laser safety will be a combination of some or all elements depending on the risk or class of laser.

Where an assessment identifies a specific risk with the laser system, then a ‘hierarchy of control’ must be followed. For non-beam hazards these are outlined within individual University policy statements. For beam hazards, the starting point for all lasers is ‘fully enclosed with fixed guarding’. 

If a risk assessment identifies that it is not practical to fully enclose the laser at all times, then it must be justified within the assessment and a suitable combination of engineering, administrative and personal protective controls identified to manage the risk. The use of personal protective equipment must always be the last option and, if necessary, there must be clear administrative controls to ensure it is correctly applied.

British standard PD IEC TR 60825−14: 2004 outlines a basic approach to laser safety for the different class of lasers. This can be summarised as:

Class 1

Class 1 laser products/systems do not require any special precautions or formal control measures. The exception is where a product consists of a totally enclosed Class 3B/4 laser system and access is required for the purpose of servicing or alignment. In this case, it should be included on the laser inventory and there should be local rules developed for that activity.

Class 1M and 2M

Class 1M and 2M products can be hazardous if the output is viewed with optical instruments. Modification of these products needs to be carefully assessed, reclassification may be necessary and the appropriate control measures detailed.

Class 2

For Class 2 laser products, protection is based on exposure being limited by the natural aversion response (0.25 sec). Simple measures such as information to users not to deliberately aim the beam at people, stare into the beam and terminate the beam at the end of its useful path will be sufficient.

Class 3R

For Class 3R products, the control measures will include:

• terminating the beam at the end of its useful path
• avoiding beam paths at eye level and where practicable enclose the beam
• instruction and training to an appropriate level
• taking care to prevent unintentional specular reflections
• where non-visible wavelengths are used, an emission indicator device is to be used to indicate the laser is energised

Class 3B and 4

By default, the beam from Class 3B and 4 should be enclosed. Open beam work should be the exception and must be supported by documenting the justification within the risk assessment.

For Class 3B or 4 lasers, each laser laboratory or experiment, as appropriate, should have its own documented local rules based upon the conclusions of a risk assessment.

The name of the departmental laser supervisor and the permitted authorised users, the extent of any laser controlled area and reference to specific protocols that are to be used should be included in the local rules.

All the above control measures indicated for Class 3R lasers should be used as well as remote interlocks, safety interlocks (where a risk assessment justifies this), key control, beam stop/shutter and the full list of user precautions outlined in the British Standard. Laser controlled areas need to be defined and warning signs used.

The local rules should be displayed in a prominent position, ideally on the entrance door to the laser controlled area.

Fully enclose the beam or if not, outline the reason within the relevant risk assessment and ensure as much of the beam is enclosed/controlled as far as is reasonably practicable.

The following outlines general levels of engineering controls. As stated, the expected starting point for all lasers is ‘fully enclosed with fixed guarding’, but the assessment should identify what level or combination of controls is relevant.

1. Fully enclosed with fixed guarding

• This would result in a ‘Class 1 by design’ product
• Guarding should be in line with BS EN 60825-4
• Guarding should ideally be localised to the beam(s) itself, such as the use of optical fibres, fixed flight tubes or enclosures directly secured around the beam
• Guarding may encompass the whole laser system, such as the use of polycarbonate or acrylic screens of suitable optical protection for the laser in use
• Guarding must be robust, secure, and ‘fit for purpose’. The material used should be appropriate to the laser classification. For lower class lasers, where the guarding is to avoid intrabeam (i.e. direct) viewing, then certain plastics or MDF could be appropriate. For Class 3B or 4 lasers, where there is an added risk from reflectance or scatter, then appropriate metal guarding should be used to ensure containment of the beam
• Guarding should be secured into position with screws that limit ease of removal, such as the use of tamper-resistant screw heads or at the very least, less common screw heads such as Torx or Tri-wing

2. Fully enclosed with removable interlocked guarding

• This would result in a ‘Class 1 by design’ product
• Where guarding may need to be opened, for instance to permit alignment, then interlocks must be fitted which connect either to a laser shutter or laser power supply. Override systems may be used to enable alignment to take place, but these must be used in conjunction with clear administrative controls and, where necessary, personal protective equipment
• Interlocks must be designed so as to ‘fail to safe’. Proprietary interlock systems are recommended, but in-house developed interlocks may be used provided they comply with the general requirements of BS EN 60825-4
• Interlocks must require some form of positive action for resetting i.e. it must not be possible to simply turn the laser back, leading to emission, by closing the interlock alone.

3. Enclosed with removable guarding

• Localised guarding, of suitable material, secured into position to restrict access to an open beam. The guards can be removed where necessary to expose the beam. For instance, where side shields are used, top covers can be applied to not only reduce exposure to the beam, but also help protect the optics
• Such guarding must be used in conjunction with appropriate administrative controls and, where necessary, personal protective equipment
• Guarding should, where possible, be compartmentalised to limit the amount of beam that needs to be exposed at any one time
• If flight tubes are used, they should be of suitable robust construction and appropriately secured. Two or more fixed clamps must be used to secure the tubes. Gravity-held shutters should be used as connectors so the beam path is closed when the tubes are removed

4. Horizontal beam lines with side shields on tables

• If localised enclosures/guarding is not possible, then, as a minimum, all laser tables must be fitted with appropriate side shields

5. Other engineering controls

• Beams must, wherever possible, be held in the horizontal plane either significantly below or significantly above the operator’s eye line. If a beam path must change level, then initial consideration must be given to increasing the height of the equipment, before the introduction of any periscope. If a periscope is required, the departmental laser supervisor must be satisfied that the optics are sufficiently rigid to prevent movement and a fixed beam stop placed at the top of the periscope to prevent someone looking directly into the beam
• All Class 3B and Class 4 lasers must be fitted with a shutter. However, where the risk assessment identifies that the existing shutter is not suitable, additional shutters should be introduced. For instance some lasers are fitted with manually operated shutters, which cannot be linked into an interlock system. In this case, it might be necessary to fit additional electrically operated shutters, but these must comply with BS EN 60825-1. Laser shutters should only be used for control of lasers over short periods of time
• All Class 3B and Class 4 lasers must be fitted with key control systems to prevent unauthorised persons operating the laser. When a laser is not in use, the keys must be removed and kept in a secure area, such as a locked key press or drawer. When lasers are not required for long or extended periods, they should be switched off
• Laser beams of Class 3R and above (and when magnifying instruments are used with Class 1M and 2M) should be terminated at the end of their useful paths using a suitable beam stop. If this is not practicable, then additional administrative control and, if necessary, suitable personal protective equipment must be worn by all those present in the area

Where engineering controls are not adequate to fully control the associated risks with a laser beam, there will be a requirement for administrative controls, which must be specified and documented to ensure individuals minimise the risk. The risk assessment should identify the additional precautions that are required and these must be recorded as Local Rules for the laser system.

In general, local rules will be required for Class 3R, 3B, and 4 lasers and any other location identified as a Laser Controlled Area. Both the supervisor and departmental laser supervisor must approve the local rules and a copy should be displayed at the entrance(s) to a Laser Controlled Area.

In addition to the Laser Registration Form (LS-1) and Laser Risk Assessment Form (LS-2) in Appendix 2, the Laser Local Rules (LS-3) can be used for this purpose, following the guidance for completing these rules given below.

1. Overview/risk assessment

• The Laser Registration Form (LS-1) and Laser Risk Assessment (LS-2) will form part of the local rules. This outlines the system and the identified hazards and risks

2. Training requirements for authorised users

• This section should outline the minimum training requirements required to undertake certain activities. It should describe any particular courses that have to be attended, along with the documentation that needs to be read and any localised training that needs to be given. The persons responsible for the training should be stated
• The names of all authorised laser users must be recorded. However, reference can be made to the separate Laser User Authorisation/Training Record (LS-4), thus enabling an ongoing update of authorised users. The activities to which a person is permitted to undertake should be recorded

3. Laser controlled area                                                                          

• Where such an area exists, the area should be stated and the extent of the area described. Details of the access restrictions should be recorded, along with the general rules for entering and working inside the area.
• Information for non-authorised users should also be recorded, stating under what circumstances they are permitted to enter (e.g. accompanied by an authorised person, use of a Permit to Work etc.)

4. Procedures                                                                                              

• The general operating procedures should clearly outline the safe operating procedures, covering:
  • operation of door entry systems, warning sign illumination, use of interlock systems, use of curtains or screens
  • pre-use inspections, including checking the optical path, guarding, interlocks, cooling system, gas connections etc.
  • general procedures, such as the use of lighting, avoidance of reflective surfaces or jewellery, seating restrictions, housekeeping, storage and the need to restrict beams from crossing circulation routes
  • instructions that need to be given to other room users
  • key control, including security requirements for the key
  • start-up procedures and checks to ensure it is operating correctly
  • ongoing operating checks
  • shut-down procedures and, if relevant, emergency shut-down procedures
  • any non-routine procedures, such as alignment or maintenance that increases the level of risk and requires additional controls must also be clearly stated.
  • permitted guarding or override procedures to be followed
  • introduction of additional screens, guarding, beam stops, or instructions
  • use of remote adjustment
  • alignment in sections and with aperture slots to reduce exposure
  • use of other low powered lasers or filters and beam splitters for reducing power output
  • use of additional visual aids such as CCD cameras or cards
  • re-installation of existing controls and checks

5. Protection measures                                                                           

• A summary of engineering and administrative controls should be given
• If Personal Protective Equipment is required, this must be clearly stated for each laser and under what circumstances. Monitoring requirements, such as routine checks, annual inspections, and assessment/local rules review should be summarised

6. Emergency plan                                                                                     

• An outline of what to do in the event of an accident involving a foreseeable beam and/or non-beam accident should be given. This should include safe isolation of the area, possible first aid assistance, procedures for transferring to the eye hospital, information to be given to the ophthalmologist and reporting/investigation arrangements

Personal protective eyewear must only be used where engineering and administrative controls cannot adequately control the risk.

Personal protective equipment in the context of laser safety normally implies the use of laser protective eyewear. As with any PPE though, there are serious limitations when relying on laser protective eyewear alone. Notably, it requires careful selection against all possible wavelengths and as such, could result in the need for more than one type of protective eyewear to cover all potential operating conditions.

It also requires very careful training and supervision to ensure the eyewear is actually worn, particularly as laser eyewear will reduce normal viewing. In some cases, this will actually increase the risk, as people might be unable to see the beam or indeed any other non-beam hazard. Most importantly, when laser eye protection is required, it generally implies there is both an eye and a skin hazard. The risk to the skin must not be discounted, although the options for protection are significantly less.

If we assume that more than one person at any one time is likely to require suitable eye protection, the actual cost of implementing personal eye protection may be greater than the cost of implementing appropriate guarding and administrative controls, albeit with a lower level of confidence in its control.

1. Laser eye protection

Laser eye protection can be in the form of either spectacles (with frames that rest on the ears) or goggles (secured by a band around the head). The latter is more suitable for those who already wear spectacles, although it is possible to incorporate the wearer’s own spectacle correction in the safety eyewear. Laser protective eyewear should be a comfortable fit to the face and provide adequate protection from laser radiation that might be incident around the edges of the frames.

Laser eye protection utilises optical filters to reduce the laser exposure that might otherwise impinge on the surface of the eye. Supervisors must ensure that any eye protection is suitable for protecting against all wavelengths or laser pulses that are in use. It should also provide an adequate level of Visible Light Transmission to ensure that normal visual tasks are not unduly affected. They should be capable of withstanding the maximum foreseeable laser exposure long enough for the wearers to take action to remove themselves from further risk. 

British Standard BS EN 207 defines the requirements for laser eye protection to reduce any accidental eye exposure to below the level of the Maximum Permissible Exposure (MPE).  However, it is sometimes desirable, with visible beams, to be able to see the beam for alignment purposes. British Standard BS EN 208 covers requirements for laser eye protection designed to reduce the exposure to the equivalent of a Class 2 laser, where protection is afforded by the natural aversion response.

Where laser eye protection is deemed necessary, then the following must be applied:

• There must be a documented in-house assessment of the required specification of eyewear for each type of laser, taking into account the varying wavelengths used and the degree of optical clarity required. The assessment must state both the optical density and scale factor attenuation for all relevant wavelengths. It is not appropriate to rely on laser equipment suppliers to undertake this assessment or specify eyewear. Eyewear must be selected against the relevant standard, BS EN 207 for general use and BS EN 208 for alignment procedures. The University has access to the LaserBee software which can be used to help with this assessment. However, individuals using the LaserBee software are strongly advised to attend the University’s Laser Safety for Research Supervisor training before carrying out these calculations.
• There must be evidence, either on the frames or in accompanying documents, that the eyewear used is CE marked and conforms to the required standard. Eyewear that does not meet these requirements must be replaced.
• The protective eyewear should be labelled indicating which laser(s) and wavelengths they are suitable for.
• Where multiple lasers are used in a single area, each set of protective eyewear must be unambiguously marked to ensure correct selection for the relevant laser.
• When not in use, protective eyewear must be stored correctly to prevent damage. It must not be left on benches but stored in protective cases or suitable racking.
• Individuals must be trained in the selection, fitting, storage, and inspection of protective eyewear.

2. Skin protection

Where there is a serious co-existent risk of skin injury from laser exposure, then protective eyewear should not be used. Alternative means of providing protection (by total enclosure of the laser radiation or filter windows) should be adopted instead. If this is still not possible, then suitable gloves, goggles, face shields etc. should be selected and used.