Aerodynamic systems or vibration can both result in the production of sound.
Mechanical shocks and friction between parts are two factors that cause vibration-induced noise (e.g., hammering, pressing, running gears, bearings, cutting tools, chutes, hoppers, etc.) incoherent moving parts (e.g., unbalanced rigid rotors) Large buildings vibrate (e.g., ventilation ducts, guards on machines, equipment supporting structures, etc.) Reflective surfaces that surround the gadgets may amplify the sound. Air or fluid flows through pipes and fans, as well as pressure drops in the air distribution system, are examples of aerodynamic sources of noise. Examples comprise: Steam discharged via exhaust valves Jet aircraft Water flowing through pipes with turbulence Fans combustion engines Please refer to the OSH Answers fact sheet for a basic explanation of sound generation: Basic Information on Noise
What actions should be taken to reduce noise in the workplace?
The following actions must be made to successfully and efficiently reduce noise in the workplace: Determine the sound's vibrational and aerodynamic sources. Determine the route taken by the noise from its source to the employee. Find out how loud each source is. Calculate each source's relative contribution to the excessive noise and rank them accordingly. It is important to control the dominant source first in order to achieve significant noise attenuation. Recognize the legal health and safety regulations' allowable exposure levels, and calculate the required sound reduction. Consider the level of sound attenuation, operational and productivity constraints, and cost when coming up with options.
How can we lessen our exposure to noise?
By removing the source of the noise (if possible), switching it out for a quieter one, making engineering adjustments, implementing administrative controls, and deploying protective equipment, the exposure to noise can be decreased.
The greatest strategy to lessen noise exposure is to incorporate it into the design from the beginning. Always strive to select equipment features that will bring the noise level down to a level that is at least tolerable. Choose quiet equipment for new installations, create a procurement policy that favors buying quiet equipment, and get rid of design defects that might enhance the noise. In already-existing workplaces where noise protection was not taken into account during the design phase, engineering modifications—changes that alter the source or the route of the sound—are the recommended means of noise control. It is commonly accepted that cost-effective solutions include reducing the source rather than reducing noise along the line. For examples, see the engineering solutions below. Personal protection equipment (PPE) and administrative controls that limit the amount of time a worker must spend in a noisy environment are examples of ways to reduce worker exposure to noise. Engineering controls may not always be seen as realistic solutions, depending on the type and intensity of the noise, the number of people exposed, and the sort of work. A combination of administrative control (limiting of exposure length) and personal protection equipment may be taken into consideration where the exposure would not warrant the adoption of more expensive alternatives. However, we must remember that administrative restrictions and the usage of PPE might not be sufficient to adequately safeguard employees (e.g., PPE may be used incorrectly or may not be used at all; administrative controls may not be followed, etc.). As a final resort for limiting noise exposure, PPE should be used. Please see our Hearing Protectors OSH Answers fact page for more details regarding hearing protection.
What engineering techniques can be utilized to lessen noise caused by vibration?
The following are a few engineering recommendations for minimizing vibration at the source: modification of the energy source, such as lowering the fan's speed or the impact's force, etc. utilizing viscoelastic materials, such as bitumastic, plastic, silicone, hard rubber, and other elastomeric polymers, to dampen or cover surfaces that vibrate owing to mechanical forces (such as chutes and hoppers). When the surface is coated with a layer of material that is one to three times thicker than the surface itself, single layer damping happens. Thin constructions can use this solution. The dampening material may be sandwiched between the wall of the equipment and a steel sheet or another abrasion-resistant material to prevent damage from friction and impact with other materials. Constrained layer treatment is what's used for things like conveyors, hoppers, machine guards, and chutes. To achieve a sufficient noise reduction, specific guidelines on the damping material's thickness in relation to the coating-target structure's thickness must be followed. reducing machine guard openings and/or filling them with acoustically absorbent material. belt drives are used in place of chain and gear drives. plastic gears are used in place of metal gears. Using gears with quiet-running tooth patterns (e.g., chevron and other helical patterns). using plastic components in place of metal ones. changing out the motors for quieter ones.
What engineering techniques can be applied to lessen noise caused by aerodynamics?
The following engineering procedures should be used, according to noise control experts, to lessen the noise caused by erratic air or water flow. Reduce fluid velocity while increasing pipe diameter. Use sizable, low-speed fans with curved blades to reduce turbulence. The relationship between the fan's speed reduction and noise attenuation is seen in the following table. Reduced speed dB of noise reduction 10% 2 20% 5 30% 8 40% 11 50% 15 (From: Best Practice in Noise Control, Health and Safety Executive, undated) When installing a centrifugal fan, stay away from elbows. Increase distance between fans and devices that may reduce efficiency and increase noise (bends, dampers) Figure 1: How to avoid turbulence (Figure from: World Health Organization, (no date). “Engineering Noise Control”) Choose quiet entraining nozzles (nozzles designed to draw and transport the air quietly) instead of simple nozzles
What are other engineering controls?
Enclosure and isolation
Noisy equipment can be enclosed in spaces or rooms that have special acoustic features – such as sound isolating, acoustic louvers, or sealed windows and doors. The degree of sound attenuation will depend on the noise reduction properties of the materials used to build the room. In many cases only the individual machine is enclosed. The enclosure can be total or partial. Partial enclosures are preferred where worker access for operating or maintenance is required. The noise attenuation offered by the partial enclosures is however lower than that of a total enclosure. An alternative to enclosure of the equipment is the enclosure of the workers. The workers may operate remotely the equipment from an isolated room. Isolation is used to reduce the sound transmitted through vibrations. The equipment is isolated from radiating surfaces by materials such as springs, elastomeric materials, cork, and foam rubber. For example: heavy vibrating machinery can be supported by isolating springs and rubber inserts, or vibrating pipes can be supported by brackets that are padded by rubber isolators or by springs. Acoustic barriersAcoustic barriers are panels made of sound absorbing material which are placed between the source of noise and the worker. Panels must be designed appropriately (e.g., panels placed in highly reflective rooms are not always effective in attenuating the noise that reaches the worker). Installation of silencers in the ducts and at pneumatic exhausts Silencers are devices that allow the fluid to pass but restrict the passing of the sound by reflecting or dissipating the sound. Sound dissipation occurs in silencers containing absorbing materials. In reflective silencers, the sound propagation is reduced due to the existence of expansion cambers (as in the car mufflers) or openings.
What other general measures can I take to control the noise?
Perform regular maintenance. Focus on identifying and replacing worn or loose parts, lubricating moving parts, and ensuring that rotating equipment does not go off balance. Substitute noisy processes with quieter ones. For example replace: Pneumatic ejectors with mechanical ones Rolling or forging with pressing Impact riveting with welding Circular saw blades with damped blades Reduce sound reverberation in the room. Reverberation happens when the sound produced in an enclosure hits a hard reflective surface. The sound reflects back in the room and ads to the original source. The strength of the reverberation decreases with the distance from the source to the reverberating surface. In some cases, the reverberated sound may dominate the original sound. In such cases, padding the reflective surfaces with sound absorbing materials will reduce the sound level. Figure 2: Sound reverberation in a room Reverberation can be reduced by arranging the equipment in the room in such a way that the equipment is not too close to too many reflective structures. The sound level of a noise source placed near hard reflective surfaces increases with 3 dB for each surface. For example, if a motor is placed directly on the floor, close to one of the walls of the room (the motor is close to two surfaces) (Figure 3, Position 2), the sound level will increase by 6 dB; if the same motor is placed in the corner of the room (close to three surfaces: two walls and the floor) (Figure 6, Position 3), the sound level will increase by 9 dB. Figure 3: Sound reflection and placement of equipment in the room Another way to reduce the sound radiation is to reduce the radiating surface (e.g. covering a transmission gear with a mesh enclosure instead of a solid box)."""