Noise & Vibration PDF

NOISE & VIBRATION Anup Meharaul [email protected] 9821 93 49 86  Definition Sound:- It is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid. In human physi...

NOISE & VIBRATION Anup Meharaul [email protected] 9821 93 49 86  Definition Sound:- It is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain  NOISE Sound is an important tool of communication Better hearing capacity is essential for better communication Human can hear sound of 20 Hz to 20000 Hz But anything in excess causes harm which is applicable for sound as well NOISE can be defined as any unpleasant and disturbing sound.  Ear The ear has 3 parts - outer ear, middle ear and inner ear. The outer ear contains the external auditory canal which carries sound waves to the eardrum The middle ear has eardrum and hammer which vibrate due to sound waves. This assembly transmits sound waves to the inner ear and regulating the sound level. Two muscle tighten the eardrum and give acoustic reflex as per brain's command. Due to high noise or long exposure , these muscles weaken resulting in hearing loss  Effect of Noise Effect of noise depends on:- Noise frequency and intensity. Total length of exposure. Length of exposure at a time. Distance from the noise source. Whether noise is continuous, interrupted, sudden or impulsive. Whether ear protector is worn or not Individual susceptibility depending on age, health etc.  Effect of NOISE Excessive noise harms overall health and may contribute to - Mental stress Physical stress Certain illness Hearing Loss or deafness Accidents Worker Productivity  Auditory effect of NOISE Hearing Loss: Hearing ability can be greatly reduced by repeated or long exposure to high noise and this permanent effect is known as noise induced hearing loss. Damage of ear drum: It ultimately result in hearing loss. May cause due to short exposure of high intensity Temporary hearing loss: can be caused by exposure to loud noise for short period, which numbs the ear cells. Fortunately, hearing is usually restored after a period away from noise. Noise induced hearing loss (NIHL) is a notifiable disease under the Third Schedule of the Factories Act 1948  Non Auditory Effect of NOISE Speech or Hearing Interference Distraction Physiological Effects : Sleep disturbance & Stress Adverse effect on work output Hypertension Cardiovascular disease Noise has effect (shrinking) on small blood vessels. It makes them narrower. This effect is known as vasoconstriction. Noise causes reduction in blood supply to various parts of the body. Noise decreases the stroke volume of the heart thereby decreasing blood circulation in the body.  Sources of Industrial NOISE Different instruments , process used in industry generates noise Impact : It is the most intense and wide spread of all industrial noise. Operations like forging, riveting, chipping, pressing, cutting, weaving, tumbling and sheared steel plates falling one over another produce such noise. Friction : Friction processes like grinding, sawing, sanding, cutting and turning on ,less lubricated bearings produce noise.  Sources of Industrial NOISE Air Turbulence : High velocity air, steam or gases cause noise. The intensity increases with the velocity of the air stream. Examples are exhaust noise from pneumatic tools and jet engines. Other Noises : In addition, there are other noises also, such as whining noise from turbines and other as per industries  Need of sound measurement & Evaluation Measurement of sound provides definite quantities which describe and rate sound. This measurement can be useful in Improving building acoustics. Permitting precise, scientific analysis of annoying sounds Giving a clear picture on identification of damage to hearing Efficiency of existing control measures suggesting corrective measures to be taken. Hearing loss can be determined by measuring a person's hearing sensitivity by audiometry. Zones as per Noise Regulation Rules Area Day dBA Night dBA Industrial 75 70 Commercial 65 55 Residential 55 45 Silence 50 40  Permissible Exposure Level (MFR-1963, Schedule XXIV) Time of Exposure per Sound level in dBA day (hours) 8 90 6 92 4 95 3 97 2 100 1.5 (90 min) 102 1 105 ¾ (45 min) 107 ½ (30 min) 110 ¼ (15 min) 115  Permissible Exposure Level (Impulse Noise) (MFR-1963, Schedule XXIV) Table 2 Peak Sound Pressure in dB Permitted number of Impulse / day 140 100 135 315 130 1000 125 3160 120 10000  Control Measures of NOISE Much noise can be eliminated by good engineering design Substitution of Less Noisy Processes: Examples are : Welding instead of riveting, mechanical forging instead of drop forging, grinding instead of chipping, belt drives instead of gears etc.  Control Measures of NOISE Segregation and Isolation: Noisy machines are removed to an area where few people work (segregation). Well insulated partition and tightly closing doors may be installed surrounding the machines (isolation). Enclosure of Noise Source : Noise producing operation can be enclosed or baffled in such a manner as to prevent dissipation of the noise into the surrounding area. Sound proofing by barrier structures.  Control Measures of NOISE Sound Absorption and Silencers: (Acoustic Insulation) High frequency sounds can be absorbed by applying sound absorbents to ceilings and walls in die form of acoustical tiles, plasters and blankets of porous materials such as glass wool Sound proofing : It includes construction or barrier structures such as walls or partitions, to safeguard the workers from external noise PPE: Ear muff or ear plug  Control Measures of NOISE Proper inspection and maintenance of equipment and machines Proper lubrication Keeping fans and engines off when not in use. Elimination of air and steam leaks. Use of rubber lining for insides of metal containers and crates to be used for material handling Job rotation Audiometry test  Vibration Vibration is a physical factor which acts on human body by transmission of mechanical energy from sources of oscillation Oscillation refers to the repeated back and forth movement of something between two positions A single oscillation is a complete movement, whether up and down or side to side, over a period of time.  Types of Vibration 1. Whole Body Vibration (WBV) 2. Hand Arm Vibration (HAV)  Effect of Vibration Vibration can cause annoyance and noise to human body and physical damage to machines and structures. Vibration can harm only if some part of the body is in direct contact with a vibrating surface viz. handle of a power tool. Effects of vibration are feeling of disoriented or displacement, giddiness, sickness, vibration disease and sometimes fatal. Whole body vibration can cause permanent damage to body or abdominal, spinal and bone damage.  Effect of Vibration Changes in bone - in carpal bones which can be seen on x-ray. Development of muscular weakness nerves. Muscular changes Whole body vibration may cause o Increase in oxygen consumption. o Affects CNS, damages internal organs. o Difficulty in maintaining steady posture. o Effects on visual acuity and narrows the field of vision. o Marked changes in bone structure White Finger (Raynaud’s phenomenon) Vibration-induced White Finger (VWF) known as dead hand or Raynaud's Phenomena is a damage to the blood vessels and nerves in fingers. It happens due to a long use of vibrating power tools such as chipping hammers, chisels, drills, concrete vibrators etc. Use of anti vibrating machine, anti vibrating gloves may help  Control Measures of Vibration Anti vibrating gloves Acoustic material Job rotation Frequent breaks Vibration Isolators can effectively reduce transmission of vibration waves Automation and remote control system Special vibration absorbing handles fitted to hand tools, springs, suspension seats and shock absorbers are useful.  Revision Define noise. Effect of noise depends on Effect of noise (Auditory & Non auditory) Permissible exposure limit of noise (Continuous & Impulse) Zones as per Noise Regulation Rules Control measures of noise & vibration Effect of vibration and control measures White finger