Download
1 / 36
E N D
Sources of Noise: • Noise can be a problem both in community and industry. Sources of community noise are mainly transportation, hobbies (amplified music), recreational (radios, TV, etc…,) and air conditioners. Examples of industrial noise are textile industries, factories, airplanes industries …etc
Noise • Definition: Unwanted sound (the most simple). • Another definition is “Wrong Sound, in the wrong place, at the wrong time.”
Physics of sound: • 1. Wave: each complete cycle of compression and rarifaction. • 2. Frequency: number of times per second that a complete vibration occurs. • 3. Intensity: a measure of maximum distance an air molecule moves from its normal position during its vibration. • 4. Pitch: that ear hears is a function of frequency • 5. Loudness:related to intensity • 6. Wave Length: depends on frequency. It is equal to speed of sound divided by frequencies and different intensities
Unit of Measuring Sound: • A dyne is 1/1000,000th of atmospheric pressure. Least audible quantity of intensity which human ear can appreciate is 0.002 dyne/cm2 or microbar while the highest appreciated is 200 dyne/cm2. • Decibel (dB): • It is a unit of comparison. A ratio between two sound pressures and it does no have an absolute value. The decibel is a logarithmic ratio between a certain pressure in microbar and the reference value. • Sound pressure level in dB = k 10 g P1 where K is a constant for correction P2
Physiology: Human ear is sensitive between 16 C.P.S. (Hz) and 20,000 Hz. Below 16 Hz vibrations are infra-audible and those above 20,000 Hz are ultra-sonic. Many animals e.g., dogs and cats can hear sounds infra-audible to the human ear. Human ear has a maximum sensitivity between 1000 and 4000 C.P.S. i.e. least amount of sound intensity will be necessary for hearing at these frequencies. As we grow older the upper limit of sensitivity decreases. Some adults are not able to detect 12,000 cycles tones or even 10,000 cycles. Below 16 cycles, one will feel rather than hear the sound since the vibrations will be within feeling ability.
Sources of noise • Noise can be a problem both in community and industry. Sources of community noise are mainly transportation, hobbies (amplified music), recreational (radios, TV, etc…,) and air conditioners. Examples of industrial noise are textile industries, factories, airplanes industries …etc.
Harmful effects of noise • Physiological: • Annoyance: The major factor causing it is the difficulty in communication and the inability to hear speech in loud noise. • Dissatisfaction: personality changes, loss of coordination and aggressiveness.
Performance: • Physical work usually not affected. • Two factors are important in this respect namely; nature of work and sensitivity of individual to noise: • Mental work usually affected specially the quality of the work e.g., more faults are met with typists • Sensitive individuals to noise usually affected in both quantity and quality of work. • Non-sensitive individuals usually not affected but they may be malingers.
Accidents & Absenteeism: • Usually increase on the basis that annoyance; visual disturbances and difficulty in hearing warning signals are important predisposing causes.
Harmful effects of noise • Physiological (Non-auditory) Effects: • Pain in the ears • Increase secretion of adrenaline, nor-adrenaline and cortisone, this may be the cause of increased incidence of duodenal ulcer in animals. • Chest feeling associated with nausea, vomiting. • Rise of both intracranial and diastolic blood pressures. • Interference with sleep • Giddiness, nausea and fatigue • Visual disturbance; narrowing of pupils – affection of colour perception – reduction of night vision
Harmful effects of noise • Auditory Effects: • The most important • a) Air-conduction deafness: • Usually occurs as a result of explosion or sudden intense noise and may result in rupture of eardrums and in severe cases dislodgment of the ossicles. This kind of deafness is reversible by healing of the tympanic membrane. It involves usually a loss of 5 to 10 dB in auditory ability.
b) Nerve conduction deafness: • Usually met with among workers continuously exposed to more than 85 dB for long periods. • Two types were notified: • 1. Transient auditory fatigue: • Suppression of hearing acuity noticed for the higher frequencies being centered about 4000 C.P.S. (Hz). Recovery begins on cessation of exposure. This type is due to reversible biochemical changes in the nerve endings of the auditory nerve. This is also referred to as Temporary Threshold Shift (T.T.S.).
Harmful effects of noise • 2. Permanent Hearing Loss: • In susceptible individuals, continuous exposure to noise causes permanent impairment of hearing first noted around 4000 C.P.S. and later on, involves other frequencies.
Harmful effects of noise • Complaints: • Tinnitus • Inability to follow conversation in a group • Inability to hear telephone • Inability to hear high pitched feminine voice • Hears his own voice less clearly and he speaks with a loud voice to hear his own words.
Factors responsible for hearing loss: • Kind of noise continuous or intermittent • In open or in closed space (closed more harmful) • Intensity of noise at different frequencies. Audible comfortable range between 20-60 dB. Discomfort occurs between 60-85 dB. Above >85 dB noise is harmful. • Duration of exposure. • Age of individual.
Diagnosis of Industrial Deafness: • History of exposure to noise • Characteristic audiogram: • Loss of hearing, particularly between 2000 and 6000 Hz. A V-shape depression, the center of which is around 4000 C.P.S. “acoustic notch”. This is to differentiate it from presbycusis due to old age and other functional and organic causes of deafness.
Control and Prevention • 1. At the source: • Substitution: of noisy process by a less noisy one • Segregation: • Isolation: to minimize the number of exposed workers • Enclosure: • Technical devices: • Suspension using rubber, springs or padding the points of friction. • Mufflers.
Control and prevention • : At the working environment • Using sound-absorbing materials that prevent reflection of sound waves. Covering the floor and walls by rubber, tile, bagasse, etc….
Control and prevention • a. Pre-placement medical examination: • Periodic audiometric examination: • Every 2 years to discover the cases as early as possible. • Health education • Personal protective equipments: Use of ▪ ear plugs ▪ear muffs • Legislation
Abnormal Air Temperature • Man is a homeotherm i.e. his blood temperature is constant (37 ± 0.5°C) whatever the environmental air temperature would be. This is in contrast to some other animals, particularly reptiles. To keep this body temperature constant, heat gained by the body from metabolism (M) must equal heat loss from the body surfaces by convection (C), radiation (R) and insensible perspiration i.e., Evaporation (E). • ( M = C + R+E )
Comfortable thermal environment conditions are those under which a person can maintain normal balance between production and loss of heart at normal body temperature and without sweating. This comfort zone temperature has been evaluated to be between 25 - 28°C
The effect of temperature on human body depends on many factors: • 1. Air temperature → which can be measured by the ordinary dry bulb thermometer. • 2. Air velocity → which is usually measured by anemometers or Kata thermometer. Kata therometer is an alcohol thermometer with a glass bulb 4 cm long and 1.8 cm in deg. to 95 deg. F. Before taking the reading, the bulb is immersed in hot water to warm it slightly above 130 deg. F and then the thermometer suspended in air. The time in seconds required for the temperature to fall from 100 deg. to 95 deg. is noted with a stopwatch. The length of time depends on the cooling power of the air.
3. Mean radiant temperature → measured by globe thermometer. The globe thermometer consists of a hollow copper bulb 6 inches (15 in diameter and is coated on the outside with black paint which absorbs the radiant heat from the surrounding objects. A specially calibrated mercury thermometer is inserted, with its bulb at the center of temperature and that of the ordinary dry bulb is a measure of the heat.
4. Relative humidity, which is the percentage of moisture present in the air; complete saturation being taken as 100. The greater the relative humidity the nearer the air to saturation. • Dry and wet bulb hygrometer is the most widely used for measuring humidity. The instrument consists of two similar thermometers – a dry bulb and wet bulb thermometers that are mounted side by side on stand. The dry bulb measures the air temperature
Air temperature: • Velocity • Effective temp • Corrected effective temp
Effects of Cold Stress: • Injury to cold may be general or local: • - General cold injury (hypothermia) is characterized by numbness, loss of sensation, muscular weakness, desire for sleep, coma and death. • - Local cold injury: a) above freezing. Immersion or trench foot. After exposure for 12 hours. b) below freezing. Frostbite, tissues freeze and ice crystals form in between the cells. • Management is done by warming the effected part using water at 44°C for 20 minutes. Intake of hot fluids promotes general rewarming.
Prevention of ill-effects of Heat: • 1. Health education. • 2. Balanced diet. • 3. High fluid and salt intake. • 4. Avoid Excessive physical fatigue. • 5. First-aid provisions. • 6. Heat Stroke management centers in concerning hospitals. • 7. Pre-placement and periodic medical examinations for workers in hot environment. Daily exposure hours must be cut down for those workers. • 8. Clothing worn should be light, white, porous, loose and better if make of asbestos. • 9. Protective goggles, shields and helmets are helpful.
4. Heat Exhaustion: occurs among persons exposed in mildly hot environment which results in diminution of blood supply to the brain as a result of vaso-dilatation of peripheral blood vessels of exposed parts. However body temperature is normal yet the main warning signs and symptoms include moist skin, low B.P, high pulse, dilated pupils, headache, giddiness, loss of power of concentration, loss of appetite, nausea, personality changes, irritability, liability to sleep and confusion. Removal to a cool atmosphere and cool water to drink will soon restore patient to normal.
7. Heat Stroke: It is one of the main health problems during Haj. Case fatality ratio reaches 40%. It is attributed to failure of heat regulating mechanism. It is characterized by very high body temperature that may rise to 44°C and profound disturbances including delirium, convulsions and partial or complete loss of consciousness. The skin is dry and hot, high pulse, normal or high B.P and keep breathing. Death is often sudden and may e due to hyperpotassemia, due to release of potassium from red blood cells that have been injured by the heat. • Treatment consists of cooling the body in the Makkah Heat Regulating Apparatus at 4-20°C. This apparatus is available in all Makkah, Mena and Arafat hospitals especially during Haj. The old trend of rapid cooling in ice water baths is stopped now, because this provokes reflex shivering which in turn increases body heat gained, metabolism and consequently body temperature.
Clinical effect of temp • Sun burn • Prickly heat • Heat exhaustion • Heat hyperpyrexia • Heat stroke • Heat syncope • Heat cramps
