[Univ of Cambridge][Dept of Engineering]


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Beginners Guide to CUED Laser Risk Assessments and Local Rules

 

The risk assessment and local rules are the most important safety items which MUST be initiated before a class 3b or class 4 laser is switched on. The basic guide below explains the methodology behind a risk assessment at the Department of Engineering. Please note that this a guide only to help complete the process.

The laser safety risk assessment can be an iterative procedure. As installations, lasers and procedures are altered, then the risk assessment and local rules should be altered as well.

The risk assessment and local rules must be submitted to the laser safety officer and be available for inspection at the site of the laser experiment.

 

The Risk Assessment process.

 

For any one using a class 3b or class 4 laser, a risk assessment and local rules must be in place before the laser is switched on. Once a risk assessment and local rules have been approved by the laser safety officer within the Engineering Department (Dr Tim Wilkinson), then the laser can be used. A copy of the risk assessment and local rules must be kept on site with the laser(s) being assessed. These documents can be requested for inspection at any time.

The purpose of the risk assessment is to identify potential hazards within an experiment and put in place as many safety controls to minimise those hazards where practicable. These controls can vary from physical barriers to training and procedural awareness.

The risk assessment is expressed through the NRPB format laser risk assessment form. This is designed to set out the risk assessment into 4 logical stages. The laser itself, the beam delivery system, the experimental system and the environment. Each of these are expressed on a separate page of the risk assessment form. Your particular system may not need all 4 sections, hence some pages may be blank or refer to others.

Each of the 4 sections has been set out to list the hazard, the person(s) at risk, the control measures and the actions (if required). The action section (second page) is there in case further work is needed to control a particular hazard. Any outstanding actions should be accompanied by a rough estimate of the date of completion. There is also an extra sheet for each section of the form to allow more detailed actions to be specified and administered.

The 4 main sections are set out as follows: 

·  The laser.  This section covers everything that might be a hazard BEFORE the laser actually emits light. This includes potential hazards such as electrocution from high voltage power supplies, flooding due to water based chilling systems, hazardous chemicals such as dyes which may be contained within the laser or even possibly the size and weight of the laser itself crushing someone (or their foot!). Typical control mechanisms will include the type of box the laser is in, how (and by whom) is it maintained, plumbed in etc.

 

·  The Beam Delivery.  This section covers the way in which the beam gets from the laser to the experimental setup. This is often a very important section, especially if the beam is propagating in free-space as this must be very carefully justified and assessed under the latest HSE rulings. The commonest type of hazard here is either eye or skin exposure to the beam. It is important as part of the assessment process to be aware of the type and nature of the hazards being assessed. What sort of eye or skin  damage might occur? To which part of the eye? Over what length of exposure, wavelength and power level? Further information about the exposure limits for both eye and skin are given in the Safe Use of Lasers: University Safety Manual Radiations Book 1 [PDF, 368KB].

What sort of controls will you put in place to avoid these hazards? The best is always to enclose the beam as much as possible. This is always the recommended course of action, however there are always extreme cases where enclosure is not possible. YOU MUST EXPLICITELY SAY WHY IN YOUR RISK ASSESSMENT. Other control mechanisms include sensible layout of components, alignment at reduced (specified) power levels, training, operating procedures and as a last defence mechanism, personal protective equipment (PPE). PPE includes goggles, gloves and protective clothing.

The basic rule of thumb is that open access to hazardous levels of laser radiation should be avoided. Any open access MUST be justifield in the local rules and operating procedures under these conditions must be listed. An example might be a laser system where normal operation is when the beam is fully enclosed, but when the system has to be aligned or adjusted, then open beam access is necessary. The local rules must contain a description of this open access, including any restrictions on the training level required, the operating procedure (normally bullet points, step by step), the level of PPE worn and also the controls in place to avoid any hazards to other members of the lab or people in the same area.

At any point where the beam may be accessed (either directly or by reflection/scatter), an estimate of the power or energy level must be included in the Risk Assessment.

·  The Experiment.  This is where the light ends up after the beam delivery system and may well have the same hazards and even be the same actual system. Once again if there is any reason for not enclosing the experiment, then this must be explained in the risk assessment and local rules. Other possible hazards in the experimental setup include; where does the beam go after the experiment with or without a sample? Are there any possible specular or diffuse reflections? What other hazards might there be such as gases, fire, ionisation etc? What are the by-products of the experiment? Harmful fume or gases?

One of the main control mechanisms will be the training and operational procedures for the experiment. This should be highlighted in the risk assessment and then defined in detail (such as bullet points) in the local rules for safe operation. This is particularly important for procedures such as alignment of the laser and beam system as there could be direct exposure to the beam and the procedural steps are the only control mechanism. This is also one of the mechanisms which must be explained when describing a non-enclosed laser system.

 

·  The Environment. This section covers the location of the laser and experiment. Those at risk might be the users or possibly others who might use the lab or stumble in by accident. Where is the system located? Who else has access? How is access to the laser/lab controlled? Are there keys, codes or cards? Who has them? Are there interlocks in place to prevent exposure if the box or lab is opened unexpectedly? Is the signage suitable to warn others in the lab?

 

Local Rules

The second part of the risk assessment process is to produce a set of local rules for safe operation. This is a compulsory part of the risk assessment process and should contain the following information:

The local rules summarise the key points from the risk assessment as well as outline any detailed procedures which must be used to operate or align a laser based experiment or system. They should also contain useful details and contacts should a hazardous incident occur.

A pro-forma set of local rules are shown here. A fully completed set for a typical PIV system are shown here.

 

If you have any queries don't hesitate to contact me:

 

Dr Tim Wilkinson

Office: Rm 107, Electrical Engineering (CAPE)

9JJ Thomson Av, Cambridge

Email: tdw13@cam.ac.uk

Telephone: 01223 748353

Mobile: 07879 458561

 

 


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Please send comments & suggestions to tdw13@cam.ac.uk

Last content change : Jan 12