Ergonomics in Design Lecture 4 PDF

Ergonomics in Design why good people design dumb things! Lecture 4 Dr. Eng. Mohamed ElWakil Human Body Senses Introduction The human body includes five senses, there are: vision, audition, cutaneous, olfactory and gustation The most important senses in the environment an...

Ergonomics in Design why good people design dumb things! Lecture 4 Dr. Eng. Mohamed ElWakil Human Body Senses Introduction The human body includes five senses, there are: vision, audition, cutaneous, olfactory and gustation The most important senses in the environment and workplace are vision and audition ADF 413 - Ergonomics in Design 2 Vision Sense The eye is the primary origan of the visual sense It is connected to the brain through the optic nerve The retina is covered with two types of light-sensitive cells known as rods and cones (130 million light sensors). ADF 413 - Ergonomics in Design 3 Visual Fatigue It is the term used to describe conditions experience by individuals when the visual sense is stressed due to incompatibility of the occupational enviromenent (e.g., poor lighting, high temperature, age of the worker) with the visual system. The effects of visual fatigue: Loss of productivity Decline in quality Increased human error Increased accident rate Visual complaint Long-term discomfort ADF 413 - Ergonomics in Design 4 Minimizing Visual Fatigue Visual capacities Lighting guidelines Controlling glare Environmental condtions Time allowed Contrast Size of visual target ADF 413 - Ergonomics in Design 5 Key terms related to visual sense Visual field: the part of one’s surroundings that is taked in by the eyes with both eyes and head are held still. ADF 413 - Ergonomics in Design 6 Key terms related to visual sense Accomodation: The action of focusing on targets at variuos distances Near-point is the closest distance that an object can be focused on without conscous accomodation Far-point is the farthest point that can be focused without conscious accommodation Amplitude of accommodation: the difference between the near-point and far- point. ADF 413 - Ergonomics in Design 7 Key terms related to visual sense Adaptation: adjustment that the pupils of the eyes make to changes in illumination Adaptation from light to dark takes about 30 minutes. Adaptation from dark to light happened much more quickly, normally within a minute ADF 413 - Ergonomics in Design 8 The Ear-Eye Line (EE line) Runs from earhole to the meeting point of the eyelids Used to describe the tilt posture of the head and the reference of the “line of sight” ADF 413 - Ergonomics in Design 9 The Ear-Eye Line (EE line) The head becomes erect (upright) if the EE line makes an angle 15 deg above the horizontal Losee angle is preferred around 45 deg when reading a text or computer screen Eye movement within about 15 deg above and below the average line of sight is comfortable for reading ADF 413 - Ergonomics in Design 10 Audtion Sense Hearing occurs when sound waves emitted from a source are collected by the outer ear and channeled along the auditory canal to the eardrum The unit of sound intensity is called decibel (dB) ADF 413 - Ergonomics in Design 11 How do we hear? Report ADF 413 - Ergonomics in Design 12 Components of ear The ear consits of three components: Outer ear (external ear) Middle ear Inner ear Factor affecting the quality and consistency of hearing Individual hearing ability Environmental factors (e.g., noise) Competing auditory signal The sound intensity (dB) and frequencies (Hz) Sound distance ADF 413 - Ergonomics in Design 13 Noise-induced hearing loss (NIHL) Noise is any acoustic phenomenon annoys the listerner, making noise a psychological and subjective issue Exposing to harmful noise (sound that are loud with a long time), the sensitive structures in the inner ear can be permanently damage resulting in NIHL ADF 413 - Ergonomics in Design 14 Noise-induced hearing loss (cont.) Acceptable and not accebtable levels of noise: ADF 413 - Ergonomics in Design 15 Noise-induced hearing loss (cont.) Acceptable and not accebtable levels of noise: ADF 413 - Ergonomics in Design 16 Experiment 1 Using NIOSH Sound Level Meter Decibel X dB Sound level meter Measure 100 dBA and above 80-90 dBA 35-70 dBA ADF 413 - Ergonomics in Design 17 Reducing the NIHL Reduce the generation of the sound by designing machine parts to minimize noise production (e.g., rubber) Impeded the transimission of noise by using barries, encapsulating noise source and using sound absorbing surface. Administrative controls (warning or rest) Personal protectivve equipment (PPE) ADF 413 - Ergonomics in Design 18 Ipods & MP3 and Hearing loss Some of research mentioned that the higher sound levels and long exposures times with using these technology could lead to hearing damage ADF 413 - Ergonomics in Design 19 Olfaction Sense Olfaction involves the sense of smell, and the major organ associated with this sense is the nose These smell receptors are connected to the olfactory nerve and transmit the sensations to the brain Examples of olfactory jobs: Safety inspector (chemical/hazard, smoke detection) Law enforcement (drug and alcohol detection) Medical workers Firefighters (gas/chemical leaks, smoke detection) ADF 413 - Ergonomics in Design 20 Gustation Sense It is the sense of taste It overlaps and depends largely on the senses of small and tactation It is not used extensively in the occupational environmental ADF 413 - Ergonomics in Design 21 Tactilation Sense The nerve endings in the skin and other parts of the body transmit sensations to the brain There are four kinds of touch sensations: Temperature Pressure Electronic stimulation Pain ADF 413 - Ergonomics in Design 22 Environmental Factors Environmental Factors There are three important environmental factors that impact on operator performance: Visual factor: light levels Auditory factor: sound levels Thermal conditions: temperature and humidity ADF 413 - Ergonomics in Design 24 Visual factors – Light levels The ability to see, particularly in an occupational setting, depends upon several factors: the level of illumination, the constrast, reflection of the work surface and glare. Illumination is the meausure of the stream of light falling on a surface This light may come frome the sun, lamps, or any other bright source. It is measured in lux and is the light density per square foot ADF 413 - Ergonomics in Design 25 Illuminance and Luminance Illuminance – the amout of light falling on a surface (lux) Luminance – the amout of light energy reflected or emitted (cd/m2) ADF 413 - Ergonomics in Design 26 Experiment 2 Using Light meter LM-3000 Lux Light Meter Pro Measure 150-300 Lux 400-600 Lux 650-800 Lux ADF 413 - Ergonomics in Design 27 Reflectance ADF 413 - Ergonomics in Design 28 Contast It is the difference between the luminance of an object and the luminance of surrounding surfaces, including its shadow Low contrast leads to poor visual performance ADF 413 - Ergonomics in Design 29 Contrast design guidelines All the objects and major surfaces in the visual field should be lit. Surface in the middle of the visual field should not have a constracst of more than 3:1 The working field should be brightest in the middle and darker towards the edges Avoid excessive contrast to the sides and below the visual field ADF 413 - Ergonomics in Design 30 Contrast design guidelines Contrast between the middle field and the edge of the visusal field should not exceed 10:1 The maximum permissible range of contrast between items with a room is 40:1 Light sources should not contrast with their backgournd by more than 20:1 ADF 413 - Ergonomics in Design 31 Visual Capacity It can be occurred due to some different tasks in industries or extreme traffic conditions (e.g., heavy rain etc.) The factors impact visual capacity: Visual actuity: the ability to detect small details and to discriminate small objects Contrast sensivity: the ability of eyes to percieve a small difference is luminance Speed of perception: time interval that elapses between the appearance of visual signal and its concious perception in the brain. It is impacted by the level of light as well as level of contrast between the object and backgroud ADF 413 - Ergonomics in Design 32 Controlling Glare Glare is the experience of intense light that enters the eye and overpowers the ability of cones and rods in the retina to distinguish shades of gray and colors There are two types of glare: Direct: occurs when light meets the eye directly from a light source such as the headlights of an oncoming car Indirect: is reflected from a surface into the eyes such as headlights of a car in your rearview mirror ADF 413 - Ergonomics in Design 33 Controlling Glare Direct glare can be reduced by placing high intensity light sources outside the cone of 60 deg around the line of sight by using several low-intensity light instead of high- intensity. Indirect glare can be controlled using shields, hoods, and visors and placed around reflecting surfaces to keep the reflected light out of the eye ADF 413 - Ergonomics in Design 34 Sources and Measurement Objectives of lighting: Suitable level of illumination Spatial balance of surface’s luminance – avoid sharp changes in luminance levels Temporal uniformity of lighting – focusing on bright and dark objects quickly Avoidance of glare Energy efficiency The age of the person concerned ADF 413 - Ergonomics in Design 35 Examples of suitable lighting levels Recommend lux examples ADF 413 - Ergonomics in Design 36 Lighting for occupational environments Filament lamps: emit head up to 60 deg and can lead to discomfort and headaches Fluorescent lights: much more efficient as they don’t produce the same level of heat Sun is considered one of the light sources ADF 413 - Ergonomics in Design 37 Noise Levels Noise is any disturbing or unwanted sound It is among the most pervasive factors impacting the workplace, home, and recreational environment It comes from occupational machinery, traffic, equipment High level of noise can lead to NIHL, stress, high blood temperature, sleep loss, distractions and lost productivity ADF 413 - Ergonomics in Design 38