Safety at Work 6 E Part 12 pdf

Applied ergonomics 635 3.9.3.5 Humidity The degree of moisture in the air needs to be controlled within certain limits. Excessive levels of moisture (high humidity) can seriously interfere with the body’s ability to sweat and can cause considerable discomfort. Where the production process requires high humidity, such as in papermaking, exposure times should be kept to a minimum. A dry atmosphere (low humidity) can cause dryness of the throat and de- hydration. Normal comfort levels of humidity lie between 40% and 50% relative humidity but may vary slightly between different types of work. Extended exposures to a relative humidity below 30% can give rise to adverse pulmonary health effects. In considering optimum temperatures and humidity account should be taken of the clothing normally worn, whether personal choice or company issue, the physical nature of the work, exposure to sources of heat (from the process or naturally from sunlight) and the amount of ventilation provided. The measurement of the thermal environment is discussed in section 3.6.2. 3.9.3.6 Lighting To be able to carry out any work effectively and accurately proper and appropriate lighting is essential. The eye reacts to strong or bright light such that areas of shadow or darkness are not seen in as much detail if at all. With all work situations suitable and sufficient lighting that enables the eye to see all the facets of the work and the surrounding area is necessary. Recommended levels of illuminance for various locations and tasks are give in section 3.7.6. While ensuring an adequate level of illumination, care must be taken to avoid positioning illuminaires where they can interfere with the clarity of vision. Typical situations to avoid include: (a) Glare and dazzle from a source of light positioned behind the object to be viewed effectively prevents the object from being seen. This can occur with low level lighting on access ways (Figure 3.9.15) or high level lights in areas of lifting operations. Similarly, viewing is interfered with if the emissions from a source of light shine directly on the eye. (b) Areas of sharp contrast since the eye reacts to the bright areas with the result that the darker areas will either not be seen or be seen only with difficulty by straining the eyes (Figure 3.9.16). Deep shadows and fluctuating levels of light have the same effect. (c) Reflections of a light source on the object being viewed whether paper, metal, desk top or monitor screens. (d) Flicker, which is a cyclic variation of light intensity that is more noticeable at frequencies below 50Hz. It is particularly noticeable at the edge of the visual field and can be distracting, cause fatigue and, in some cases, epileptic seizures. 636 Safety at Work Figure 3.9.15 Disability glare from a light fitting (Courtesy The Stationery Office) Figure 3.9.16 Sharp contrast between exterior light and interior shadow (Courtesy the Stationery Office) Applied ergonomics 637 (e) Stroboscopic effect occurs when the flicker from fluorescent lamps coincides with the speed of rotating objects making them appear stationary. This can be avoided by utilising twin tube fittings wired 90° out of phase. 3.9.3.6.1 Types of illuminaires Sources of artificial light split broadly into two types: (i) point sources such as the tungsten filament lamp where a glass envelope containing either a vacuum or a filling of halogen, mercury or sodium vapour at pressure. Since the filament is heated to white heat to provide the illumination the surrounding glass envelope can get hot. Adequate arrangements for cooling are needed and the lamp should not be located near flammable materials. Because this type of illuminaire is a point source of light it is important that it does not: ᭹ create areas of bright light and deep shadows, ᭹ reflect on work surfaces and ᭹ mask information on VDU monitors. The gas used to fill the bulb – mercury, sodium or halogen – creates a colour bias in the light emitted. This must be allowed for in processes where colour recognition is important, such as electrical wiring, paint colour matching, etc. (ii) fluorescent strip light fittings in which the light emanates from the fluorescent coating on the inside of the tube. Although giving a much more even spread of light than tungsten lamps they can still cause reflections on surfaces. This effect can be reduced to a minimum by the use of diffusers and louvre fittings. Problems that are met with this type of illuminaire include: ᭹ flicker and ᭹ stroboscopic effect. The positioning of illuminaires is important to ensure they do not create interference with viewing. Where interference does occur, the object being viewed should be moved or the illuminaire repositioned. Advice on the type and positioning of luminaires is given in a guidance note 5 . 3.9.3.7 Ventilation The presence of contaminants in the atmosphere is a potential source of distraction and annoyance. They may be there as a result of fumes or dust leaking from the process or of someone’s personal habits such as smoking. With contaminants there is also an associated potential health risk (from hazardous fumes and dusts, tobacco smoke, etc.). Legislation 7 requires the supply of a sufficient quantity of fresh or purified air. It does not specify quantities but guidance 5 suggests a minimum of 5–8 l/s per occupant (18–29 m 3 /h). However, this does not allow for the effects of the production process nor the type of work so these quantities may need to be increased. Fresh air is that drawn from outside but care needs to be taken to ensure the intake point is clear of exhaust outlets or other sources 10kg F u ll h e i g h t 20kg Shoulder height 25kg Elbow height 20kg Knuckle height Knee height 10kg 5kg 10kg 15kg 10kg 5kg 638 Safety at Work that might contaminate the air or be hazardous or evil smelling. Purified air refers to recirculated air that has been ‘conditioned’ but the Code of Practice 5 recommends that some fresh air should be added to it although again no quantity is specified. In many situations, an adequate supply of fresh air can be obtained from an open window but in the larger open plan offices and workshops some form of forced air ventilation may be required. The outlets from ventilation systems should be arranged so that they do not play on an individual since this can be a source of annoyance and also interfere with sweat rates to become a health hazard. Outlet velocities and directions of flow should ensure that the air velocity at any one workstation is not so high as to be unpleasant or uncomfortable. In general, the more active the work an airflow as high as 0.5 m/s can be tolerated. However, for sedentary work the flow should be less than 0.1 m/s while in jobs requiring deep concentration even that level of air movement can be distracting. 3.9.4 Manual handling Ideally, if objects have to be moved it should be done mechanically. Where this is neither technically feasible nor economically viable manual handling will have to be employed. Manual handling is a known and well documented source of occupational injury and in spite of publicity and training accident attributed to manual handling remains the highest cause of absences. Legislation 8 sets out the actions to be taken to reduce the hazards with advice on ways to achieve them given in a Code of Practice 9 . The ability to handle loads varies with the position of the load with respect to the body and Figure 3.9.17 indicates a suggested range of maximum Figure 3.9.17 Suggested maximum loads at various distances from the body Applied ergonomics 639 weights that can be lifted and carried. The values given are typical and will need to be adjusted to suit the physique and ability of the operator. It is important to remember that it is not only what is picked up but how. For manual handling, work should be arranged so that: ᭹ the load to be lifted is the smallest technically feasible and economi- cally viable; ᭹ loads that cannot be broken down to safe weights are handled by mechanical means such as sack barrow, special purpose handling equipment, lift trucks, etc.; ᭹ the level from which the load is lifted should be as high as possible up to waist level; ᭹ ideal height for picking up a load is waist level; ᭹ if necessary an intermediate resting platform is provided; ᭹ close body approach is possible to the delivery platform to prevent the need to lean with the load; ᭹ the final delivery level is not above shoulder height; ᭹ for placing loads at higher than shoulder level a lift truck or suitable step ladder is used. Where loads have to be carried manually, the floor surface should be level, smooth and in good condition. Where manual handling has to be carried out from the sitting position, the ability to lift may need to be reduced to as little as 20% of the equivalent load when standing. 3.9.5 Repetitive actions Actions that involve putting repeated loads on particular muscles, especially on the arms and the wrist, can cause a number of muscular conditions variously referred to as repetitive strain injury (RSI), tenosyno- vitis, carpal tunnel syndrome, work-related upper limb disorder, etc. Symptoms exhibited include soreness in the muscles that initially disappears when ceasing work but rapidly returns when work is recommenced. If the same work is continued, the condition can become very painful and have long lasting effects. On jobs where this condition is a known or suspected risk arrange- ments should be made to: ᭹ eliminate the type of work that causes the condition and replace it by alternative work methods; ᭹ restrict the time engaged on the suspect activity; ᭹ rotate jobs during the shift so that operators carry out a number of different functions using different muscles; ᭹ ensure tools and equipment used on suspect operations are, and are maintained, in good condition and do not require excessive force for their proper use; ᭹ build into the work programme adequate rest periods; ᭹ instruct supervisors and operators in the symptoms and the action to be taken if they occur, i.e. move to alternative work and seek medical advice. 640 Safety at Work 3.9.6 Plant design Layout of plant should ensure that any movements the operators need to make are direct, free and unimpeded by other parts or equipment. Operator work areas should be clear, clean, well lit with a good floor surface. If the work platform is at a raised level, it should have a safety rail and be provided with access steps if the height warrants. The treads of steps should be wide enough to accommodate the full length of a normal shoe. Steps at an angle greater than 45° should be avoided, but if space limitations dictate steeper steps, proper permanent ladders with hand rails should be provided. Any step up (or down) should not be greater than 25 cms (10 ins). Steps higher than this can greatly increase the strain on the knee and hip muscles with consequent increased fatigue. Adequate space should be left around each machine to permit free and easy movement for operating it and to allow for maintenance activities. Walkways should be identified by suitable lining and not allowed to be used for storage purposes. Services, such as air, water, electrical power, necessary for the work being carried out should be conveniently situated for the operators’ use. Machines in sequential operations should be positioned to require the minimum amount of handling of product. Wherever possible that handling should be automated or by mechanical means. The emission of noise and fumes by machinery which can affect the operator and those on adjacent machines should be reduced to a minimum. 3.9.7 Controls and indicators Controls and instruments are the main interface between the operator and the machine or plant. In the design and layout of them: ᭹ The movement of all controls must be consistent with the natural movement of the limb operating it. ᭹ Movement of a control in a clockwise direction, to the right or towards the operator should cause an increase in the machine function – the exception to this is a tap or valve where clockwise movement results in a decrease in output, i.e. the valve is shut. ᭹ Coarse adjustment and adjustments that require some force should utilise the full arm, leg or hand movement. ᭹ Where foot pedals are used, if actuation is by movement of the whole leg the pedals should be arranged so they can be operated by either foot. If movement of the foot only is required it should be by pivoting on the heel. In both cases the arrangement should ensure that the operator is not required to stand on one leg for long periods. ᭹ Quick, precise or fine adjustments that require little physical effort should be by the fingers. ᭹ Hand operated controls should be located at a height between waist and shoulder level and be in clear view. Applied ergonomics 641 ᭹ Controls that have to be actuated frequently should be positioned adjacent to or within easy reach of the operator’s hands. Other controls should be within easy arms reach. ᭹ Adjacent hand or finger operated controls such as push buttons, toggle switches and rotating knobs should be spaced at least 25 mm (1 in) apart to prevent inadvertent operation. ᭹ In the layout and shape of control buttons: ᭹ start buttons should be recessed into the control panel, shrouded, or gated to prevent inadvertent operation; ᭹ stop buttons should be positioned adjacent to the start control, stand proud above the panel surface and be red in colour; ᭹ emergency stop buttons should be red, of the mushroom headed type and lock in the open circuit condition when actuated. ᭹ The function of all control actuators should be clearly indicated either by words or symbols. ᭹ Where the condition of the control is important and may need to be known without looking at it, a datum mark such as a small pin or notch should be made in the mounting panel and a matching pin or notch made in the control handle. The two should line up at either neutral or normal operating position so any deviation from it can easily be sensed. ᭹ Control handles for separate operations should have a unique tactile identity 10 . ᭹ Instruments that are important should be in clear view of the operator, ideally at eye level or within 20° of the normal eye line but must not interfere with the operator’s view of the machine or plant. ᭹ The movement of the condition indicator of an instrument should be consistent with the change in condition, i.e. increase in the condition shows as a clockwise movement or, in linear gauges, to the right or upwards. ᭹ Instruments that measure associated parameters should be positioned together and arranged so that the pointers or condition indicators all lie in the same orientation for normal operation allowing any deviant reading to be seen easily. ᭹ Where controls have to be actuated over periods of time with little body movement, seating should be provided for the operator and the positioning of the controls and instruments arranged accordingly. Controls that are operated by the feet fall into two categories, those in which the whole leg is moved giving only a very coarse degree of control and those using the foot only, when a fine degree of control can be achieved. In the former case, movement of the foot is from the hip allowing only a basic ON/OFF type of control without any intermediate positioning, such are used for the initiation of a press stroke or the foot pedals of an organ. Where a fine degree of control over the operating range is necessary this can be achieved by pivoting the heel of the foot on the floor or suitable rest. An even finer degree of control, such as the accelerator pedal in a car, can be achieved by providing a support at the outer side of the foot about which the foot can pivot. If a foot control is operated from a 642 Safety at Work standing position, the arrangement should ensure that part of the body weight can be taken by the operating foot, or if this is not possible, the control should allow operation by alternate feet to prevent the excessive strain imposed when one leg takes the full body weight. 3.9.8 Noise and vibrations In all walks of life sound is a necessity, for communication, for warning and leisure enjoyment (music and the theatre). Unfortunately there are differing views about what sound is useful and what is an adequate amount of sound. Any unwanted sound is regarded as noise and as such should be eliminated or reduced to the lowest level possible. In general sound that interferes with people’s enjoyment of their private lives and pursuits becomes a nuisance and has been legislated against 11 . But excess sound can also interfere with concentration at work and become a potential hazard as well as reducing the operating performance of those subject to it. Examples of typical noise levels are shown in Figure 3.5.2. Noise in an area is likely to be a hazard if it is necessary, when standing 1 metre apart, to have to shout to carry on a conversation. Where there appears to be a noise problem, sound level readings should be taken to establish the extent of the problem. The presence of noise has long been recognised as one of the factors that reduces the quality of working life. While the human brain can ‘tune out’ consistent and/or irrelevant noises it can only do this up to a point. As noise levels rise so they become more insistent and invasive. Similarly unexpected changes in even quite low levels of noise can stimulate a subconscious response and, in some cases, break completely the current train of thought. The problems of noise from machinery and advice on the measures to combat it are well documented in HSE publications 12, 13 and it is not proposed to iterate them here. Vibrations on the other hand, where there is a finite movement of the plant, equipment or a pulsing of the air, are much more invasive and can interfere with certain body organs ultimately causing ill health. Measures that can be taken to reduce the distracting effects of noise include: ᭹ elimination of sources of noise; ᭹ if that is not possible then: ᭹ enclose the source of noise in a sound proof room but ensure adequate cooling and ventilation is provided; ᭹ provide sound havens or soundproof operating rooms ensuring there is adequate ventilation; ᭹ use sound absorbing screens and barriers; ᭹ separate work areas from noise sources; ᭹ position potential noise sources away from work areas – the frequency hum from a transformer can be very invasive; ᭹ directing the outlet ducts from ventilating systems, dust extraction systems, etc. away from affected areas. This can include private house bedrooms where fan exhausts can become a nuisance and subject to abatement orders; Applied ergonomics 643 ᭹ in offices, replacing noisy matrix and daisywheel printers by inkjet or laser printers; ᭹ installing floor covering that deadens the sound of footsteps partic- ularly the clacking of heels on a hard floor; ᭹ ban the use of personal radios in the workplace – they can interfere with the reception of warning signals; ᭹ in open plan offices, the segregation of those with penetrating telephone voices; ᭹ arrange for operations that generate noise, such as use of pneumatic drills, etc., to be carried out in ‘non-working’ hours. This includes work on part of the structure of reinforced concrete framed buildings since noise travels through the concrete; ᭹ as a last resort, provide suitable personal protective equipment. Mechanical vibrations generated by the movement of parts of the plant and machinery can travel through the machine and be transmitted to the building and those working in it. Air vibrations occur as a pulsing of the air and can be generated at the outlet of fans and blowers and from the exhaust of slow running engines. Both mechanical and air vibrations can be a health hazard since they can induce sympathetic vibrations in certain human organs resulting in damage to that organ. The transmission of mechanical vibrations can be reduced by: ᭹ mounting the equipment on anti-vibration mounts; ᭹ providing flexible connections between the vibrating plant and other equipment. Air vibrations can be reduced by: ᭹ changing the speed of the fan or blower; ᭹ installing diffusers; ᭹ changing the flow resistance of the air circuit; ᭹ ensuring the intake to the fan is not obstructed. 3.9.9 Stress Stress has many causes including an inability to do what ought to be done or failure to meet the targets set. The cause may be within the individual or it may be imposed from outside. Internally caused stress can only be resolved by the individual himself but imposed stress causes can be reduced or eliminated by following ergonomic principles. The build up of stress in an individual will make him less efficient in his work and may even make him a safety hazard. To optimise an individual’s performance the stress suffered should be reduced to a minimum. Typical stress situations, with possible ways to resolve them, include: ᭹ working at a machine led rate which is either faster or slower than the individual’s natural work rate. Wherever possible suitable adjustments should be made to the machine speed; 644 Safety at Work ᭹ being required to undertake work which is either well below or well above his inherent ability. This may require a re-assessment of the operator and moving to other more appropriate work; ᭹ being given inadequate or excessively complex instructions about his job. Instructions should be realistic and comprehensive and in terms and language that the operator can understand; ᭹ being prevented from working at his own natural rate. Some means should be provided to adjust the demanded rate of work; ᭹ having to do a job in a less efficient manner than he knows it can be done. Listen to the operator’s suggestions and act on them or explain why not; ᭹ being uncertain of his position in the organisation and not knowing who his bosses are. Provide training in the role and position within the company covering areas of responsibility, extent of authority, subordinates and superiors, etc.; ᭹ having to wait for materials or data. Improve planning and expediting; ᭹ being unable to understand and follow work methods. Further training and the provision of back-up information; ᭹ working in software in which he has not been properly trained and without back-up. Ensure adequate training and provide competent back-up to resolve queries; ᭹ at loggerheads with his supervisor. A personal matter to be resolved by the individuals or by separating them; ᭹ being pressurised by his peer group; ᭹ under a threat of redundancy without having any details. Ensure kept informed of the latest position; ᭹ family affairs; ᭹ frustration with lack of progress on agreed action affecting his work and working conditions. Initiate suitable action or explain why it has not been possible; ᭹ lack of recognition for ideas put forward. Improve human relations in the company; ᭹ irritating noises. Investigate and eliminate; ᭹ boredom from repetitive uninteresting work. Re-assess ability and move to more demanding work. 3.9.10 Display screen equipment (DSE) The ergonomic aspects of the use of DSEs has been well documented in the HSE’s guidance publication 14 particularly those aspects concerned with the physical comfort of the users and operators such as: ᭹ chair with adjustments for seat height and back rest; ᭹ suitable foot rest; ᭹ adequate leg room below work table; ᭹ adjustable screen both rotating and tilting; ᭹ document holder to reduce amount of eye movement; ᭹ limit on time of continuous operation; ᭹ training in the use of the software with back-up immediately available in case of queries; [...]... done is never as great as the energy expended, as some of the energy is lost in overcoming 66 4 Safety at Work friction The ratio of work done to energy expended is the mechanical efficiency of the machine and is always less than one Power is the rate of doing work and is measured in joules per second: 1 joule per second = 1 watt of power 1 kWh = 3 .6 ϫ 1 06 joules 7 46 watts = 1 horsepower The rate at. .. Compressible fluids When gases are compressed, work is done on them and they acquire considerable potential energy as pressure They also become hot and it is sometimes necessary to provide cooling to ensure that critical temperatures are not exceeded Conversely when gas pressure is released, the gas does work or gives up energy and heat and becomes cold This latter effect is the basis by which refrigerators work. .. temperature of the gas rises In air compressors where there is likely to be oil present the temperature of the compressed air must be kept below a certain level to prevent ignition of the contained oil Conversely, when the pressure of a gas is decreased, the temperature drops, a condition that can be seen with bottles of LPG where a frost rime forms and where in cold weather there is a danger of the... by their ‘coefficients of expansion’ that vary with the different substances The heat needed to raise the temperature of different solids varies and can be determined from its ‘specific heat’ Problems can arise where dissimilar metals are welded together that have different specific heats and different coefficients of expansion Allowance has to be made for differential expansions where different metals... However, at the earth’s surface the weight of the air of the atmosphere exerts a pressure of 1 N/m2 or 1 bar Beyond the earth’s atmosphere there is no pressure and this is taken as the base for the measurement of pressure in absolute terms Thus: gauge pressure = absolute pressure –1 N/m2 or absolute pressure = gauge pressure +1 N/m2 The pressure at the top of a mercury barometer, where the force due... the pressure will increase If the reaction is exothermic and the temperature increase is not controlled there is a risk that the pressure in the vessel could rise above the safe operating level with consequent risk of vessel failure, a situation that may be met in chemical processes that use autoclaves and reactor vessels This general law applies with variation when gases are compressed in that the... together, have little kinetic energy and vibrate relative to each other A solid has form and a rigid surface as a result of the strength of the cohesive forces between the molecules As a solid is heated the vibrations of the molecules increase and the solid expands Eventually a temperature is reached where the kinetic energy allows the molecules to slide over one another and the solid becomes a liquid... substance (e. g acetylene) Air, carbon dioxide and a number of other gases which dissolve in water become more soluble as the pressure increases or the temperature decreases Increase in temperature or decrease in pressure causes the dissolved gases to come out of solution, e. g tonic water or fizzy lemonade This is why hydraulic systems need venting A similar 66 0 Safety at Work condition arises with divers... matter, whether solid, liquid or gas, exhibits properties that follow patterns that have been determined experimentally and are well established and proven This section looks at some of the factors that influence the state of matter in its various forms 4.1.4.1 Temperature Temperature is a measure of the hotness of matter determined in relation to fixed hotness points of melting ice and boiling water... machines work is given in either horsepower or kilowatts Pressure is unreleased potential energy since when contained in a pressure vessel the fluid exerts equal and opposite forces on the vessel walls but no movement takes place Pressure is independent of the shape of the vessel and is exerted at right angles to the containing surfaces With gases the pressure is virtually the same throughout the containing . such should be eliminated or reduced to the lowest level possible. In general sound that interferes with people’s enjoyment of their private lives and pursuits becomes a nuisance and has been legislated. occur, i .e. move to alternative work and seek medical advice. 64 0 Safety at Work 3.9 .6 Plant design Layout of plant should ensure that any movements the operators need to make are direct, free and. made to the machine speed; 64 4 Safety at Work ᭹ being required to undertake work which is either well below or well above his inherent ability. This may require a re-assessment of the operator and