c06_work_equipment_workplace_machinery_COMPLETE

Question 1

The Supply of Machinery (Safety) Regulations 2008 (SMSR) and the Provision and Use of Work Equipment Regulations 1998 (PUWER) originate from

Answer 1

Article 95 and Article 137 Directives respectively Article 95 DirectivesHarmonisation of productstandardsArticle 137 DirectivesWorking conditions

Question 2

The aim should be to eliminate any risk throughout the foreseeable life cycle of the machinery, including transport, assembly, dismantling, disabling and scrapping. The following principles should be applied, in the order given: 3

Answer 2

(1) Eliminate or reduce risks as far as possible (inherently safe machinery design and construction). (2) Take the necessary protective measures in relation to risks that cannot be eliminated. (3) Inform users of the residual risks due to any shortcomings of the protective measures adopted, indicate whether any particular training is required and specify any need to provide personal protective equipment. Design danger out (inherently safe design)  Design safety in (guards and protection devices)  Protect end user from residual risks (IT IS / PPE)

Question 3

The responsible person must ensure that a risk assessment is carried out in order to determine the health and safety requirements which apply to the machinery. The machinery must then be designed and constructed taking into account the results of the risk assessment. The risk assessment and risk reduction process should: 5

Answer 3

 Determine the limits of the machinery, which include the intended use and any reasonably foreseeable misuse thereof.  Identify the hazards that can be generated by the machinery and the associated hazardous situations.  Estimate the risks, taking into account the severity of the possible injury or damage to health and the probability of its occurrence.  Evaluate the risks, with a view to determining whether risk reduction is required, in accordance with the objective of the directive.  Eliminate the hazards or reduce the risks associated with these hazards by application of the hierarchical approach specified in the principles of safety integration.

Question 4

Establishing the limits of the machinery should take into account 4

Answer 4

 Use  Space  Time  Other

Question 5

Risk is the combination of the probability of occurrence of harm and the severity of that harm, where the probability of occurrence of harm, is a function of: 3

Answer 5

(1) the exposure of person(s) to the hazard (2) the occurrence of a hazardous event (3) the technical and human possibilities of avoiding or limiting the harm.

Question 6

The following aspects require careful consideration during risk estimation: 8

Answer 6

 Persons exposed  Type, frequency and duration of exposure  Relationship between exposure and effects  Human factors  Reliability of safety functions  Possibility to defeat or circumvent safety measures  Ability to maintain safety measures  Information for use.

Question 7

Risks are reduced in accordance with the three stage hierarchical approach, discussed earlier as part of the principles of safety integration: 3

Answer 7

(1) Inherently safe design measures - the hazard is eliminated or the risk reduced by design or by the substitution through less hazardous materials and substances, or by application of ergonomic principles. (2) Risk reduction by the application of safeguarding and complementary protective measures, of a type that adequately reduces risk for the intended use and reasonably foreseeable misuse. (3) The provision of information for use to address any residual risk (operating procedures, safety information, training and PPE).

Question 8

Adequate risk reduction is considered to be achieved when: 7

Answer 8

 All operating conditions and all intervention procedures have been considered.  The hazards have been eliminated or risks reduced to the lowest practicable level.  Any new hazards introduced by the protective measures have been properly addressed.  Users are sufficiently informed and warned about the residual risks.  Protective measures are compatible with one another.  Sufficient consideration has been given to the consequences that can arise from the use of a machine designed for professional/industrial use, when it is used in a non-professional/non-industrial context.  The protective measures do not adversely affect the operator’s working conditions or the usability of the machine.

Question 9

The CE marking requirements under the Machinery Directive relate to new machinery. However, if a machine is modified to such an extent that new hazards are anticipated, this will be considered a significant modification and the same measures will need to be taken as for new machinery. The process can be broken down into the following stages: 7

Answer 9

(1) Categorise the product. (2) Check the application of additional directives. (3) Ensure that requirements of safety regulations are met. (4) Perform the risk assessment. (5) Compile the technical file. (6) Issue the declaration of conformity. (7) Affix the CE mark.

Question 10

With reference to European machinery standards, explain the meaning of the following categories of standard: Type A, Type B1, Type B2 and Type C AND give a practical example in EACH case. 10 marks

Answer 10

Type A standards are concerned with basic safety concepts and design criteria and apply to all machinery. Examples quoted could have included general safety requirements contained in EN ISO 12100 and the principles for risk assessment ISO 14121 (EN 1050). Type B standards relate to particular safety aspects in support of the general principles of the A standard. B1 standards for example refer to safety distances, such as in the design of fencing or the approach speed that is required for calculating the safety distance for safety light curtains or multiple light beam safety devices. B2 standards deal with the performance requirements of special protective devices, and contain notes on the design and testing of components or devices such as stop buttons, safety door switches, safety mats and safety light curtains. Type C standards describe specific risks and the measures for reducing these risks at specific machines or machine types. A relevant example would have been BS EN 693 concerned with hydraulic presses. A general point which should have been made was that if a C standard exists for a particular machine type, it takes priority over a B or A type standard. If, however, no C type standard exists for a machine being designed or manufactured, risk reduction in accordance with A and B standards should be made.

Question 11

In relation to a newly designed machine that falls within Schedule 2 Part 4 Annex (iv) of the Supply of Machinery (Safety) Regulations 2008, outline the procedures that must be followed, and the requirements that must be met, before such a machine is placed on the market for sale in the European Economic Area. 10 marks

Answer 11

The machine designer/manufacturer should to ensure the machine satisfies the Essential Health and Safety Requirements (EHSRs), by reference to relevant EN standards, and should compile a technical file. If the machine is consequently found to be safe, and has been designed and manufactured according to EN standards, the manufacturer may either ensure that the machine is manufactured in accordance with the technical file by carrying out internal checks, or developing a quality assurance (QA) system and having it approved by an approval body, or obtaining EC type approval from an approval body. When any of these procedures is completed satisfactorily, the approved body issues either an EC type examination certificate or approval for the quality assurance system. If the machine is not designed and manufactured according to EN standards, the manufacturer may again either develop a QA system and have it approved, or obtain EC type approval from an approval body. A successful completion of either of the above will again result in the issue of an EC type examination certificate or approval for the QA system. Finally the manufacturer should ensure the machine conforms with other non-machinery directives before issuing a declaration of conformity and fixing the CE mark to the machine.

Question 12

Hazards associated with the use of machinery are normally categorised as 2

Answer 12

mechanical (to do with the moving parts) or non-mechanical (to do with all other aspects).

Question 13

Mechanical hazards associated with a machine, machine parts or surfaces, tools, work-pieces, loads, or projected solid or fluid materials These can be summarised and remembered with the acronym

Answer 13

EnTICE. En tanglement T raps – crushing, shearing, and drawing-in I mpacts C ontacts – cutting / severing, friction / abrasion, stabbing / puncture E ejection, including high pressure fluid injection.

Question 14

Non-mechanical hazards arising from the use of machinery include: 10

Answer 14

 Electrical (Element C8)  Thermal (Element B10)  Noise (Element B6)  Vibration (Element B6)  Radiation (Element B7)  Materials and substance (Element B1)  Ergonomic (Elements A7, B9 and C5)  Slip trip (Element C1)  Environmental hazards (Element C4)  Hazard combinations (Minor individual hazards can combine to be equivalent to a significant hazard).

Question 15

The primary causes of material failure are

Answer 15

operating loads, such as stress, impact and frictional loading, and environmental conditions, such as corrosive, high temperature, and high energy environments, with combinations of both often leading to rapid wear-out and failure.

Question 16

_____ & _____ are the key measurements used to understand the properties of the materials that objects are made of.

Answer 16

Stress and strain

Question 17

Stress describes the relationship between the applied force and the area over which it acts. It can be expressed as a formula:

Answer 17

S = F/A

Question 18

Stress is measured in

Answer 18

Newtons per metre squared (Nm-2), which is the same units as for pressure).

Question 19

Strain is the measurement of the change in the shape of the material / object as a result of the application of the stress force. The precise definition of strain depends on the type of deformation produced. The simplest case is of forces of tension applied to opposite ends of a wire or rod which stretch or extend the length of the wire or rod. In this case:

Answer 19

Strain = Length change / original length

Question 20

Strain is also caused by the application of stresses other than tension, notably: 4

Answer 20

compression, bending, shearing and torsion,

Question 21

Materials can fail in more than twenty different recognizable ways. The following common failure modes are specified on the NEBOSH Diploma syllabus: 5

Answer 21

 Fatigue  Ductile failure  Brittle fracture  Buckling  Corrosive failure.

Question 22

Fatigue failure occurs when

Answer 22

a material fractures into two or more pieces after being subjected to a cyclic stress (fluctuating load) over a period of time.

Question 23

The fatigue failure mechanism involves three stages:

Answer 23

 Crack initiation - usually at a ‘material inhomogeneity’, such as notch, groove, surface discontinuity, flaw or other material defect.  Crack propagation - the applied stress concentrates until it exceeds the local strength of the material and produces a crack.  Material rupture - when the crack has weakened the material to a point such that it can no longer support the applied load it will rupture, by shear or by tension.

Question 24

Ductile failure

Answer 24

Ductile materials that are subjected to a tensile or shear stress will elastically or plastically strain to accommodate the load and absorb the energy. Yielding occurs when the material’s yield strength is exceeded and can no longer return to its original shape and size. This is followed by ductile fracture, which occurs when the deformation processes can no longer sustain the applied load.

Question 25

Brittle fracture occurs when

Answer 25

mechanical loads exceed a material’s ultimate tensile strength, causing it to fracture into two or more parts without undergoing any significant plastic deformation or strain failure.

Question 26

Buckling occurs when

Answer 26

a material subjected to compressive or torsional stresses can no longer support the load, and it consequently fails by bulging, bending, bowing or forming a kink or other unnatural characteristic.

Question 27

Corrosion is

Answer 27

the deterioration of a metal or alloy and its properties due to a chemical or electrochemical reaction with the surrounding environment.

Question 28

Galvanic corrosion is

Answer 28

a form of corrosive attack that occurs when two dissimilar metals (such as stainless steel and magnesium) are electrically connected, either through physically touching each other or through an electrically conducting medium, such as an electrolyte. When this occurs, an electrochemical cell can be established, resulting in an increased rate of oxidation of the more anodic material (lower electrical potential). The opposing metal, the cathode, will consequently receive a boost in its resistance to corrosion.

Question 29

Outline the characteristic features of, and factors that promote, the following types of materials failure: (a) brittle fracture 5 marks (b) ductile fracture 5 marks

Answer 29

(a) A brittle fracture generally occurs without warning or prior evidence of distress. It is a crystalline structure failure with minimal plastic or elastic deformation. There are generally characteristic ‘chevron’ marks from the point of initiation and the failure is sudden from rapid stress loading. The factors promoting a brittle fracture are high tensile stresses, residual or built in stresses, sudden loading which does not give the material time to deform plastically, case hardening, low temperatures and the degree of brittleness of the material. (b) A ductile fracture generally has a smooth fracture surface with plastic deformation of the material before final fracture. There is evidence of necking and the final fracture is often brittle because there is insufficient material left to sustain a load. This type of failure generally occurs as the result of a single stress overload although other promoting factors include high temperatures, cold work hardening and the plasticity of the material.

Question 30

NDT encompasses a range of test processes that produce no harmful effects on the material or structure under test. NDT techniques include: 6

Answer 30

 Simple visual examination of surfaces  Dye penetrant techniques  Radiography (Gamma and X-ray)  Ultrasonic testing  Eddy currents  Magnetic particle inspection.

Question 31

Dye penetrant outline

Answer 31

The liquid penetrant is drawn into the surface-breaking crack by capillary action, and excess surface penetrant is then removed. A developer (typically a dry powder) is then applied to the surface, to draw out the penetrant in the crack and produce a surface indication. Fluorescent penetrants are usually used when the maximum flaw sensitivity is required, and can detect cracks as narrow as 150 nm.

Question 32

Radiography outline

Answer 32

The radioactive source is placed on one side of a specimen and a photographic film on the other side, an image is obtained on the film of the thickness variations in the specimen, whether these are surface or internal.

Question 33

Ultrasonic outline

Answer 33

Ultrasonic methods use beams short wavelength (1 to 10 mm) and high-frequency (0.1 to 20 MHz) mechanical waves (vibrations) transmitted from a small probe and detected by the same, or other, probes.

Question 34

Eddy current testing outline

Answer 34

Eddy current testing places a coil carrying an AC current close to the specimen surface, or around the specimen. The current in the coil generates circulating eddy currents in the specimen close to the surface, which in turn affect the current in the coil by mutual induction. Flaws and material variations in the specimen affect the strength of the eddy currents.

Question 35

Magnetic particle inspection (MPI) outline

Answer 35

The specimen is magnetised either locally or overall, and if the material is sound the magnetic flux is predominantly inside the material. If, however, there is a surface-breaking flaw, the magnetic field is distorted, causing local magnetic flux leakage around the flaw. This leakage flux is displayed by covering the surface with very fine iron particles, applied either dry or suspended in a liquid. The particles accumulate at the regions of flux leakage, producing a build-up which can be seen visually, even when the crack opening is very narrow. Thus, a crack is indicated as a line of iron powder particles on the surface.

Question 36

X-ray radiography is a non-destructive testing (NDT) technique that is sometimes used to examine the internal structure of fuel tanks in the wings of large passenger aircraft. (a) Outline the principles of operation when using X-ray radiography for this application. 4 marks (b) Other than visual inspection, explain why different forms of NDT might not be appropriate for this application. 4 marks (c) Identify TWO disadvantages in the application of X-ray radiography. 2 marks

Answer 36

(a) Radiation would be generated by a portable electrically powered machine such as a generator focussed into a beam by lead shielding. The beam would be directed to penetrate the wing skin to reach a film or electronic sensor placed inside the tank on the opposite side of the wing. An image of the intervening structure within the wing is created on film after photographic development or on the electronic sensor after electronic processing, with defects being revealed by the contrast between light and dark areas. The image has light areas where less radiation reaches the film or sensor after passing through unbroken or sound structure, whereas the image has darker areas where more radiation reaches the film or sensor through voids or cracks in a structural element which is faulty. This part of the question was not well answered with many candidates showing confusion between radioactive sources and x-rays generated by a machine. (b) 4 other forms of NDT which might not be appropriate for the scenario include:  gamma radiography, which would be impractical and too expensive  eddy current can experience spurious defect indications and does not provide a permanent record  dye penetrant shows only surface cracks with accessibility to tanks being impossible  magnetic particle testing does not work on non-ferrous metal and there would again be the problem of tank inaccessibility  there would be no indication of fault location from tap testing. (c) Disadvantages in the application of x-ray radiography include:  the manual handling of heavy equipment  the possibility of exposure to x-rays training in interpretation skills is necessary for the operators  its use is relatively expensive.

Question 37

The NEBOSH Diploma specifies the following four major accidents to illustrate the causes and effects of materials failure:

Answer 37

 Brent Cross 1964 (Overloading, bending moments, buckling of crane jib)  Markham Colliery 1973 (fatigue failure of winding engine brake rod)  Littlebrook D 1978 (corrosion of hoist cage wire ropes)  Ramsgate Walkway Collapse 1994 (fatigue failure of bearing mount welds due to torsional stresses ‘roll’).

Question 38

A serious accident occurred when a threaded steel rod in the braking mechanism of a hoist broke. An investigation revealed that the cause of the breakage was fatigue failure. (a) Outline the mechanism and characteristics of fatigue failure. 6 marks (b) Identify THREE factors which can contribute to such a failure AND for EACH factor outline ONE circumstance in which it may occur. 6 marks (c) Outline the measures that could have been taken to minimise the likelihood of such a failure. 8 marks

Answer 38

(a) Characteristics of fatigue failure include:  crack propagation from points of stress concentration  fluctuating stress environments  characteristic conchoidal fracture pattern (beach marks), which progress as narrow rings at low load, extending at full load. There is little or no deformation prior to the final failure which may be ductile or brittle. (b) Factors which could give rise to fatigue failure in practice include:  stress concentration particularly at sharp corners and holes  surface and sub-surface defects such as flaws, cracks, occlusions and impurities  design and fatigue strength issues  residual stresses imposed during manufacture or assembly  the effects of factors such as corrosion or temperature. (c) Measures to minimise the likelihood of fatigue include:  those connected with design, manufacture and installation involving the correct specification of materials and components to match service conditions, correct assembly and quality assurance  the maintenance, inspection and examination (with NDT) particularly of critical components and their replacement at planned intervals  measures connected with use such as avoiding abuse and remaining within designed operational limits, the provision of training and instruction for those involved in the use and the keeping of service history records.

Question 39

Regulation 11 of PUWER places an absolute duty on the employer to take effective measures to either:

Answer 39

 prevent access to any dangerous part of machinery or to any rotating stock-bar  to stop the movement of any dangerous part of machinery or rotating stock-bar before any part of a person enters a danger zone.

Question 40

The hierarchy for machinery guarding, which should be applied so far as is ‘practicable’ is: 3

Answer 40

 Fixed guards to the extent that it is practicable to do so, but where or to the extent that it is not, then …  Other guards or protection devices to the extent that it is practicable to do so, but where or to the extent that it is not, then …  Protection appliances.

Question 41

Protection devices do not prevent access to the danger zone but stop the movement of the dangerous part before contact is made. They will normally be used in conjunction with a guard. Examples include: 4

Answer 41

trip devices, light curtains, pressure-sensitive mats and two-hand controls.

Question 42

Protection appliances are used to

Answer 42

hold or manipulate a work piece at a machine while keeping the operators body clear of the danger zone. They are commonly used in conjunction with manually fed woodworking machines.

Question 43

All guards and protection devices should be designed, fitted and used in accordance with the following principles: 8

Answer 43

 be suitable for the purpose for which they are provided  be of good construction, sound material and adequate strength  be maintained in an efficient state, in efficient working order and in good repair  not give rise to any increased risk to health or safety  not be easily bypassed or disabled  be situated a sufficient distance from the danger zone  not unduly restrict the view of the operating cycle of the machinery, where a view is necessary  allow safe access for maintenance work, restricted to the area where the work is to be carried out and, if possible, without having to dismantle the guard or protection device.

Question 44

A fixed guard may be: (2 types)

Answer 44

enclosing guarddistance guard

Question 45

a distance guard which does not completely enclose the danger zone but prevents access by virtue of its dimensions and distance from the danger zone, for example: 2

Answer 45

• a perimeter fence (Figure 6.22) - a tunnel guard (Figure 6.23).

Question 46

Advantages and disadvantages of fixed guards

Answer 46

Advantages  Low cost.  Easy to monitor by visual inspection.  Can only be defeated by intentional act.  Minimal on-going maintenance – no moving parts or complex systems.  May offer some protection from other hazards such as noise, dust or ejected parts and materialsDisadvantages Removal of the guard does not stop the machine.  If the guard needs to be removed regularly for maintenance it is likely to be left off.  May impede operators view.  May impede ventilation.

Question 47

The second level in the hierarchy allows a choice from a broad range of guards and protection devices. Other guards include: 4

Answer 47

 Interlocked (moveable) guards  Adjustable guards  Self-adjusting guards  Automatic (sweep) guards.

Question 48

The second level in the hierarchy allows a choice from a broad range of guards and protection devices. Protection devices include: 4

Answer 48

 Mechanical trip devices  Active opto-electronic devices (AOED) such as light curtains  Pressure-sensitive mats  Two-hand controls.

Question 49

Advantages and disadvantages of interlocked guards

Answer 49

Advantages  Convenient where frequent access is required.  Allow safe access when opened – machine is powered down. Disadvantages Complex systems requiring regular testing and maintenance.  Components may fail in use.  May be defeated (spare keys, stuck contacts etc.).  Failure may not be apparent until after an incident.

Question 50

Advantages and disadvantages of self-closing guards

Answer 50

Advantages Disadvantages  Automatically adjust to accommodate the work piece. Disadvantages Only provide a partial guarding solution – still allows some access to the dangerous parts.  Require regular inspection and maintenance.

Question 51

Advantages and disadvantages of adjustable guards

Answer 51

Advantages Disadvantages  Probably the only practical solution where a work piece needs to be brought into contact with a cutting tool, especially if used in conjunction with a protection appliance. Disadvantages Have to leave part of the cutting tool accessible for it to do its job.  May be set up to accommodate largest job of a shift, rather than adjusted to best setting for each job.  Can be removed and machine is still useable.

Question 52

(a) Outline what is meant by the term ‘fixed guard’ and ‘automatic guard’ in relation to machinery safety AND identify the circumstances where each type of guard might be appropriate AND give a typical example in EACH case. 8 marks

Answer 52

(a) A fixed guard is a guard which is not connected in any way to the controls, motion or hazardous condition of a machine and is fixed to the machine in such a manner, for example with screws, nuts or by welding, that it can only be opened or removed by the use of special tools or by the destruction of the means of fixing. It is an appropriate method of providing protection against mechanical hazards when infrequent or no access is required to dangerous parts of a machine during its normal operation. A typical example of its use would be as a guard for a belt and pulley drive. An automatic guard is a guard connected to the machine mechanism which, when the machine is operated, pushes the operator away from the danger area. It is generally used on slow moving, long stroke machines such as certain types of press.

Question 53

(b) To ensure that machine operators are adequately protected, describe the factors to be considered in the design and use of: (i) fixed guards (ii) automatic guards 6 marks 6 marks

Answer 53

(b) (i) With respect to the design features of a fixed guard, factors include:  the material of construction, which should be sufficiently robust to  withstand the rigours of the workplace and be able to contain any ejected material, but still allow sight of the process when required  the method of fixing, usually requiring the use of a special tool for the guard’s removal  the need to ensure that any necessary openings in guards are such that they do not allow access to the dangerous parts  the need to address the possibility of the guard reverberating and exacerbating a noise problem. (b) continued … Factors to be considered in the use of fixed guards include:  monitoring and supervision to ensure that the guard is not compromised  safe systems of work for the carrying out of maintenance operations with the guard removed  the provision of information and training for both operators and maintenance staff. (ii) For automatic guards, factors to be considered would be:  the compatibility of the guard with the machine function and the convenience of its use  the speed of movement of the machine since this type of guard would be inappropriate on fast moving machines  the height and reach of the operator  the force of movement of the guard together with the possibility that the operator might be crushed between the guard and an adjacent fixed object or structure  the possibility that the guard might fail to danger  the ease or difficulty with which the guard could be defeated  the training that would have to be given to operating and maintenance staff.

Question 54

Advantages and disadvantages of two handed controls

Answer 54

Advantages  Ensures the operator is in a safe position. Disadvantages Only protects the operator.  Can be defeated.

Question 55

Advantages and disadvantages of light beam devices

Answer 55

Advantages Disadvantages  Allow an unobstructed view of the machine. Disadvantages Not suitable in all environments, for example: dust may trigger false positive trips.  No physical barrier therefore no protection from ejections or non-mechanical hazards.  Do not protect anyone working inside the danger zone.

Question 56

(a) Describe the following hazards associated with an abrasive wheel: (i) mechanical (ii) non-mechanical 5 5 marks

Answer 56

(a) (i) mechanical hazards associated with an abrasive wheel include:  Contact with rotating wheel  Trap between wheel and tool rest  Entanglement around axle  Ejection of parts of work piece or from burst wheel (ii) non-mechanical hazards associated with an abrasive wheel include:  Dust  Sparks / fire  Electricity  Noise  Vibration  Stability of machine  Positioning / working posture

Question 57

(b) Describe the protective devices and guards that would be found on an abrasive wheel to minimise the risk of injury from mechanical hazards. 4 marks

Answer 57

(b) Protective devices and guards against mechanical hazards would include:  wheel enclosed as much as possible by a fixed guard  adjustable guard over exposed part of wheel (if fixed guard not appropriate)  interlocked guard to ensure the machine can’t operate until the guard is in place, that opening the guard will stop the machine and that closing the machine doesn’t itself restart the machine.  transparent screens fitted to fixed machines to intercept sparks and particles (as an alternative to eye protection).

Question 58

(c) Explain the risks associated with an abrasive wheel arising from its deterioration. 3 marks

Answer 58

(c) Risks associated with abrasive wheels include:  injury from flying abrasive and metallic particles  inhalation of dust from dry grinding operations  noise and vibration related injury  physical injury from flying fragments if the wheel burst (centrifugal force/speed increase)  wheel breakage

Question 59

(d) Explain why employees require training for activities involving an abrasive wheel. 3 marks

Answer 59

(d) Employee training in all aspects of mounting and using abrasive wheels is essential to ensure that employees are aware of the hazards, risks and precautions, including how to store, handle and transport them, inspect for damage, to assemble and balance correctly before use, to adjust and use suitable PPE while using. Note: More in the HSE guide Safety in the use of abrasive wheels (HSG17)

Question 60

A manually operated lathe is to be fitted with a Computer Numeric Control (CNC) system. Outline: (a) additional hazards this may introduce 4 marks (b) measures required to minimise the risks associated with these hazards 6 marks

Answer 60

(a) The fitting of a computer numeric control to a manually operated lathe would introduce additional risks such as:  an increase in the speed of the machine and the potential rise in noise levels that could accompany this increase  the possibility of unexpected movements or aberrant behaviour  errors in programming and software  risks arising during setting and teaching operations together with those arising from the operators’ unfamiliarity with the system. (b) Measures that would be required to minimise the risks include:  the completion of a risk assessment for the new system  the provision of fixed or interlocked guards to prevent access during the automatic cycle  the provision of manual operation for setting and cleaning such as a hold to run system  the relocation of the controls outside the danger zone  the provision of additional training for operators and maintenance staff  updating the instruction manual for using, setting, cleaning and maintaining the machine  carrying out regular testing of the software and screening for RF interference.

Question 61

All machinery must be marked visibly, legibly and indelibly with the following minimum particulars: 6

Answer 61

 the business name and full address of the manufacturer and, where applicable, the manufacturer’s authorised representative  designation of the machinery  the CE marking  designation of series or type  serial number, if any  the year of construction, that is the year in which the manufacturing process is completed.

Question 62

Instructions must be drafted in accordance with the principles set out below 4

Answer 62

(a) The instructions must be drafted in one or more official Community languages. (b) The instructions must be marked and verified as ‘Original instructions’ or ‘Translation of the original instructions’, as appropriate. (c) The contents must take into account any reasonably foreseeable misuse of the machinery, as well as the intended use. (d) Where the machinery is intended for use by non-professional operators, the wording and layout of the instructions for use must take into account the level of general education and acumen that can reasonably be expected from such operators.

Question 63

PUWER Regulation 8 places a duty on employers to

Answer 63

make available all relevant health and safety information and, where appropriate, written instructions on the use of work equipment to their workforce.

Question 64

Regulation 23: Markings The employer has a duty to ensure that work equipment is marked in a clearly visible manner with any marking appropriate for reasons of health and safety. This might include: 6

Answer 64

 Identification of stop and start controls.  Marking the maximum rotation speed of an abrasive wheel.  Marking the maximum safe working load (rated capacity) on lifting equipment.  Indicating the content of gas cylinders by colour coding.  Marking storage and feed vessels containing hazardous substances to show their contents, and associated hazards.  Colour coding service pipework to indicate contents.

Question 65

Warnings or warning devices may be appropriate where risks to health or safety remain after other hardware measures have been taken. They may be incorporated into systems of work (including permit-to-work systems), and can enforce measures of information, instruction and training. A warning is normally in the form of a notice or similar, for example: 3

Answer 65

 positive instructions (example: hard hats must be worn)  prohibitions (example: not to be operated by people under 18 years)  restrictions (example: do not heat above 60 ºC).

Question 66

If equipment has to run during a maintenance operation and this presents risks, appropriate controls should be introduced to reduce the risk, for example: 3

Answer 66

 provision of temporary guards  limited movement controls  crawl speed operated by hold-to-run controls.

Question 67

A SSW is required when

Answer 67

hazards cannot be eliminated and a degree of risk remains after technical control measures are introduced.

Question 68

The systematic analysis of a task may be undertaken in various ways: 3

Answer 68

 A job safety analysis (JSA) may be used to break the task down into its component steps and identify hazards at each stage.  A MEEP analysis may be used in conjunction with, or independent to, a JSA and uses the headings materials, equipment, environment or people (MEEP) to prompt consideration of potentially unsafe conditions, and unsafe acts.  Other approaches consider what, who, where and how, or the 4 Ps – premises, plant and substances, procedures and people.

Question 69

A simple SSW may be defined verbally, as a written procedure or become a formal Permit-to-Work (PTW) (discussed later), depending on the level of risk and the needs of the organisation. In all cases the SSW should: 5

Answer 69

 Consider the preparations and authorisations necessary before beginning work.  Ensure the job sequence is logically and clearly planned.  Specify safe methods for undertaking specific activities.  Specify safe means of access and egress if relevant.  Consider the end of activity tasks such as dismantling and disposal.

Question 70

In order to install a large item of machinery such as a turbine rotor, it is sometimes necessary to perform adjustments while the rotor is in motion. These adjustments are necessarily undertaken with the rotor in an unguarded condition. Outline the elements of a safe system of work for this activity. 10 marks

Answer 70

The elements of a safe system of work for carrying out the operation described in the question include:  the use of experienced workers fully trained in the systems to be adopted, since this is not a task to be carried out by the young or inexperienced  the provision and use of a single, one-piece, close fitting overall with no external pockets, together with arrangements to ensure there are no other entanglement hazards present, such as the wearing of jewellery, or long hair  the use of temporary guards or the isolation of parts of the machine which are unnecessarily exposed  where practicable the use of jigs to ensure workers’ hands are distanced from the unguarded rotor  the provision of a ‘stand by’ man in direct contact with the person carrying out the work, with means of immediate communication such as telephone or radio to ensure an emergency response, should the need arise  the provision, close at hand, of emergency stop or braking arrangements  the use of an inching device to minimise the free rotation period, or using the slowest speed possible consistent with the task  the provision of non-stroboscopic lighting  the introduction of a permit to work to formalise the establishment of the safe system of work  the erection of barriers and signs to prevent the close approach of non-involved personnel.

Question 71

The essential features of permit-to-work systems are: 5

Answer 71

 Clear identification of persons responsible for authorising particular jobs (and any limits to their authority) and persons responsible for specifying necessary precautions.  Clear identification of the types of hazardous work.  Clear and standardised identification of tasks, risk assessments, permitted task duration and supplemental or simultaneous activity and control measures.to-w  Training and instruction in the issue, use and closure of permits.  Monitoring and auditing to ensure that the system works as intended.

Question 72

The basic process involves:  Issue by a competent issuing authority, setting the parameters of the permit and confirming that precautions are in place.  Acceptance by a competent worker (performing authority), confirming understanding of the work to be done, hazards involved and corresponding precautions.  Handback of the PTW, by the performing authority, confirming that the work has been completed to plan.  Cancellation of the PTW by the issuing authority confirming the work has been tested and the work area returned to normal use.  Additional procedures are required for

Answer 72

extension of agreed time limits if necessary, and for managing shift handovers.

Question 73

Isolation (and energy dissipation) of external energy sources may require management of the following: 5

Answer 73

 Mechanical power transmission: by isolating clutches, by removal of drive belts or chains, or shaft sections. Scotching may also be used.  Electrical power: by isolating switches by removal of fuses, or by removal of plugs from sockets. Earthing or short-circuiting may also be needed.  Hydraulic or pneumatic power: by isolating valves, by electrical isolation of hydraulic pumps, or by disconnection from pneumatic mains. Open venting to atmosphere may also be required.  Services: isolation of water, steam, gas or fuel supplies. Draining or venting may also be needed.  Process and material supplies: isolation of process lines and line blinding or blanking off. Draining or venting may also be needed.

Question 74

The following sources of residual energy storage or material internal to the machine or equipment may also need to be dealt with, as follows. 6

Answer 74

 Mechanical power: allow flywheels or high speed rotating parts, such as centrifuge bowls, to run down, and to minimize the potential energy of other parts.  Electrical power: discharge of capacitors, disconnection of stand-by batteries, or earthing and short-circuiting of high voltage circuits.  Hydraulic power: discharge of accumulators, or relaxation of pressurized pipe-work.  Pneumatic power: discharge of air pressure throughout the system (except where used for hold-up. Note: where hydraulic or pneumatic hold-up devices have been provided for mechanical parts, those selected should be of high reliability.  Services: residual steam, gas or fuel may need to be vented, purged or drained.  Process and material supplies: emptying, venting, purging, draining and/or cleaning may be required before entry.

Question 75

The overall reliability of equipment depends on both the reliability of all components and the way in which they are arranged, which may be as: 3

Answer 75

 Series systems  Parallel systems  Combinations of both series and parallel systems - i.e. mixed (complex) systems.

Question 76

The overall reliability of a series system is calculated by

Answer 76

by multiplying the reliability of each individual component

Question 77

A designer is designing a safety-critical, electrical control system. The system consists of a number of components arranged in series. One of the components is a detector which has a reliability of 0.95. The designer is considering installing two identical detectors in parallel to improve the reliability of the system. (a) Calculate the improvement in reliability that using two identical detectors in parallel would give compared with a single detector. 4 marks (b) Outline the issues that would need to be considered when assessing whether the proposed extra detector in parallel should be adopted. 3 marks (c) Assuming that the decision is taken to use two detectors in parallel, outline other ways in which the reliability of the control system could be improved. 9 marks (d) The designer has been warned that his assumptions of improved reliability from two detectors might be undermined by common mode failure. Outline the meaning of ‘common mode failure’ AND outline why it may affect the reliability as calculated in (a) above. 4 marks

Answer 77

(a) The following calculation should have been produced to demonstrate a full understanding of the problem: The reliability of the parallel components: 1 – [(1 - 0.95)(1 - 0.95)] = 1 – (0.05 x 0.05) = 1 – 0.0025 = 0.9975 …or when rounded to 3 decimal places … 0.998 or 99.8% The improvement in reliability would therefore be: 0.998 – 0.95 = 0.048 or 4.8% (b) Issues that would need to be considered include:  the probability of system failure and its consequences  legal requirements and advice contained in industry and HSE codes of practice and guidance  the initial cost of the additional detector  the subsequent expense connected with the detector’s on-going maintenance and inspection  risk tolerability criteria such as those contained in ‘Reducing Risks, Protecting People’. (c) Additional ways in which the reliability of the control system could be improved include:  the use of design stage failure tracing techniques, such as HAZOP  introducing purchasing quality control arrangements to ensure the most reliable detectors are used  using two different types of equipment to minimise the risk of common mode failure  ensuring the system components are tested before installation and that they are correctly installed by competent personnel  arranging for the introduction of procedures for the periodic inspection, testing and maintenance of the system, including the replacement of components within their useful life  providing training to employees in operating the system and in fault detection using indicators or warnings to indicate component failure. (d) Common mode failure is as a type or cause of failure that could affect more than one component at a time, even when the components are supposed to be arranged to operate independently of each other. The reliability calculations for components in parallel assume independent failure modes and the existence of common mode failures would mean that the actual reliability was less than that calculated.

Question 78

HRA steps 4

Answer 78

 Identify all points in a sequence of operations at which incorrect human action, or inaction (‘sins of omission’), may lead to adverse consequences for plant and/or for people.  Assign a degree of probability on a numerical scale to each event in the chain.  Aggregate the probabilities to arrive at an overall figure for the probability of human failure for the whole chain of events.  Identify steps that need to be taken to reduce the likelihood of failure at certain points by introducing organisational, procedural, ergonomic or other changes.

Question 79

The major limitation of HRA techniques is the potential inaccuracy of the assigned values. Different techniques use different sources of data, but essentially the figures are derived from: 3

Answer 79

 expert opinion  historical data  experimental data. Each approach is prone to various selection and measurement biases.

Question 80

Practical methods for improving system reliability include: 7

Answer 80

 Use of reliable components  Quality assurance  Parallel redundancy  Standby systems  Minimising failures to danger  Planned preventive maintenance  Minimising human error.