Noise Control on Farms

Agdex#:	700
Publication Date:	02/96
Order#:	96-033
Last Reviewed:	02/96
History:	Original Factsheet
Written by:	Michael Toombs - P.Eng / OMAFRA

Table of Contents

1. Introduction
2. Legal Aspects  
3. Acoustic Concepts
4. Methods of Noise Reduction
5. Preventing Propagation of Noise

Introduction

Noise is unwanted sound - the wrong sound at the wrong time or place. Most people think of rural areas as quiet places and they usually are. But some agricultural activities in rural areas produce a lot of sound that can interfere with the activities of people nearby. This sound may become a noise, especially in the evening and during normal sleeping hours.

When noise problems develop and are unresolved, they can result in bad relations between farmers and neighbours. The neighbours may suffer a loss of enjoyment of their property or worse, their health may suffer due to a loss of sleep or due to anxiety.

The best solution is to avoid problems before they develop. Like odours from manure-handling, it is not possible or necessary to eliminate all of the noise produced by certain farm operations. However, a farmer can minimize the noise problem. Good planning and design of operations and activities, and a common sense consideration of others should avoid most noise problems. In other words, put yourself in your neighbours position and decide if you would like to listen to the noise you generate. The results are beneficial to all - less disturbance and fewer complaints and bad feelings. Also, where a farmer reduces noise on the farm, it will certainly help preserve his or her own hearing.

Noise generated by a source may be annoying because it is heard over and above the level of the "ambient" or surrounding background sound level at a particular location. Sound level limits are therefore expressed as the difference between noise from a source and the ambient noise. In urban areas, the ambient noise is usually made up of pervasive road traffic noise that creates the background "urban hum". In rural areas, the acoustic environment is normally made up of natural sounds such as the wind blowing through the trees, running water, birds, insects, etc. Road traffic is infrequent in most cases.

The most effective noise-control measure is to keep a noise source as far away as possible from neighbours who might not appreciate it.

Planning of noise-reduction measures should be aimed at fulfilling one or more of the following three requirements:

1. Reduction of the possibility of hearing damage.
2. Creation of a quieter working environment.
3. Avoidance of annoyance to third parties.

Although the first measure is overriding, all three requirements should be met with noise-control techniques.

Legal Aspects of Noise Control

In Ontario, the law concerning noise goes back a number of years. Noise was originally treated as an inconvenience, nuisance, or interference with the use of property. In response to public concerns, municipal authorities became involved in addressing complaints and restraining the activities of noisemakers by developing and enforcing municipal bylaws to regulate or prohibit noise. In 1971, sound and vibration were defined as contaminants under the Environmental Protection Act (EPA). In 1974, the EPA was revised to empower local municipalities, subject to approval of the Ministry of Environment (MOE), to pass bylaws regulating the emission of sound and vibration. The Model Noise Control Bylaw was developed by MOE to help municipalities pass noise bylaws and it is used as a guideline for MOE staff when conducting an assessment or investigation.

In 1988, the Farm Practices Protection Act, commonly called the "right to farm" legislation, was established to protect farmers who carry on normal farm practices from court action against odour, noise or dust complaints under common law of nuisance. If a noise resulting from a farm practice is in contravention of any Act or bylaw such as a noise-control bylaw, then the Farm Practices Protection Act would not apply.

Acoustic Concepts

In order to control noise it is helpful to understand the following acoustic concepts.

Sound

Sound is a wave motion that occurs when a sound source sets the nearest particles of air in motion. The movement gradually spreads to air particles farther from the source. Sound propagates in air with a speed of approximately 340 metres/second (1115 feet/second). In liquids and solids the propagation velocity is greater - 1,500 metres/second (4920 feet/second) in water; 5.000 metres/second (16400 feet/second) in steel.

Noise

A sound that is not desired is usually called noise.

Frequency

A sound wave's frequency expresses the number of vibrations per second in units of Hertz (Hz). Audible sound for humans lies between 20 Hz and 20,000 Hz.

Decibel (dB)

The intensity of sound is measured in decibels (dB). The human ear can detect a sound level change of 1 dB. If a sound level is increased by 10 dB, the ear perceives it as doubling in loudness. A drop of 10 dB is perceived as halving in loudness. Common sound levels are listed in Figure 1.

Figure 1. Decibel Levels of Common Sounds

• 0 dB = Acute threshold of hearing
• 15 dB = Average threshold of hearing
• 20 dB = Soft whisper
• 30 dB = Leaves rustling
• 40 dB = Rural ambient background
• 65 dB = Normal conversation
• 69 dB = In bin grain dryers and aeration fans
• 80 dB = Heavy traffic
• 90 dB = Grain dryers
• 100 dB = Tractor under load
• 110 dB = Chain saws

Receptor

Person who hears the sound on any property other than the property where the sound is generated.

Addition of Noise from Several Sources

Noise from different sound sources combine to produce a sound level higher than that from any individual source. Two equally intense stationary sound sources produce a sound level that is 3 dB higher than one alone.

Attenuation by Distance

Sound that propagates from a stationary source in air reduces by 6 dB for each doubling of the distance from the noise source as illustrated in Figure 2.

Temperature and humidity affect sound levels to a limited degree. Sound levels are affected by natural features such as the slope and roughness of the ground and the type of vegetation. The surface of the ground can either reflect sound, as does concrete, or absorb sound, as does a hay field. The net effect of attenuation by distance is illustrated by the noise contours around a grain dryer in Figure 3.

Methods of Noise Reduction

There are three main ways to reduce noise on the farm.

1. Reduce noise at the source.
2. Change to quieter methods of work.
3. Prevent or reduce noise propagation.

The first two methods are primarily management techniques, and the third, which usually requires site specific engineering, will be dealt with in more detail in the next section.

Figure 2. Attenuation By Distance - A point source such as a grain dryer produces 90 dB at one metre. The sound level at two metres will be 84 dB. At four metres it will be 78 dB, etc.

Figure 3. Noise Contours (dB) Around A Farm Dryer.

The following guidelines were developed for specific agricultural noise sources, assuming typical operations and average acoustical conditions.

Bird-Scaring Devices

These devices are used to scare birds away from orchards, vineyards, crops and other areas where birds can do damage. Two types are in common use: a) propane-fired bird bangers, and b) electronic warblers employing high frequency impulse sound (from 2000 Hz upwards) at varying impulse rates.

Electronic warblers generate less objectionable noise than propane-fired bird bangers. The following measures will help to reduce the noise impact on neighbours:

1. Use bird-scaring devices only when required for protection of specific crops and only when a problem is evident.
2. Operate bird-scaring devices only between dawn and dusk.
3. Where possible use directional bird-scaring devices aimed away from neighbours.
4. Maintain the devices properly to avoid continuing noise when the bangers are shut off.
5. Locate devices as far from neighbours as possible.
6. At fur-bearing animal ranches, avoid the need for bird-scaring devices by screening pens to reduce the attraction of birds.
7. Erect a noise barrier to keep noise from neighbours.

Grain Drying Operations and Hay Dryers

Grain dryers produce noise from fans, burners and the movement of grain by mechanical means. The fan/burner unit is the main source of noise. Older dryers with vane axial heating fans generate higher noise levels. Newer models, especially those that use a centrifugal air-foil blade fan, are only about half as loud. Older dryers can be refitted with newer, quieter fans. Noise produced from hay dryers is from the fans.

The noise impact on neighbours can be reduced by following these measures:

1. Locate the structures as far as possible from neighbours using existing barns or silos as noise buffers if possible.
2. Locate fans on the side of the building or dryer facing away from neighbours and direct the fan intake axis away from neighbours.
3. Use fans with low decibel ratings or fans with adjustable pitch blades that provide some control of noise level.
4. When possible, avoid night time operation of dryers.
5. Use noise mufflers.
6. Enclose elevator fan/motor units.

Livestock Ventilation Fans and Greenhouse Operations

Farm ventilation fans should be directed away from residences. Mechanical ventilation fans and boiler units are the main sources of noise from greenhouses. A boiler unit operation does not usually result in serious noise problems since most exhaust outlets are fitted with effective mufflers, and the installation itself is indoors. Follow the recommendations given for grain drying operations to reduce the noise impact on neighbours.

Mechanical Farm Equipment

Since most farm machinery is not stationary, no specific separation distance can be recommended. However, a number of actions can be taken to reduce or avoid noise problems:

1. Ensure the tractor muffler is functioning as designed.
2. Where possible, confine night time activity to those areas most remote from neighbours.
3. Avoid leaving tractors idling for prolonged periods near neighbouring homes.
4. Where possible, avoid night time operation of irrigation pumps located near neighbours.
5. If the equipment is to be used as a stationary power source, use an enclosure.

Preventing or Reducing the Propagation of Noise

In addition to the management techniques listed above, several noise-control methods involve the modification of the sound propagation path through application of acoustical materials, enclosures, barriers and silencers.

Acoustical Materials

There are two basic categories - absorbing and barrier materials. Absorbing materials include mineral wools, felt and polyurethane foams. They have high sound-absorption qualities and generally soft porous surfaces. Absorbing materials reduce reverberant and reflected sound, but not the transmission of sound. Absorbent materials should only be used in close proximity to sound sources and should never be used as shields, barriers or enclosure walls.

Barrier materials may include wood, metals, glass and concrete. The denser the material, the more the sound transmission is reduced. To provide maximum acoustical effectiveness, it is necessary that an enclosure or a barrier be absolutely air-tight. Even a slight opening will cause a noticeable degradation of noise-abatement effectiveness.

Enclosures

Complete or partial enclosure is often the most effective measure for solving a noise-control problem. Enclosures should be constructed of a combination of absorbing and barrier materials. An enclosure that has one side or a very large opening is considered a partial enclosure. To be effective a partial enclosure must interrupt the line of sight path between the noise source and the receptor, and it must absorb the sound reflected from the source.

Barriers

Barriers, usually walls or fences, are generally only effective in deflecting some of the noise away from a receptor. Barriers are most effective when placed close to the noise source or the receptor, and when the barrier material has a high density as in concrete. Since sound can bend around barriers, they can be considered relatively ineffective for agricultural noise sources.

Silencers or Mufflers

There is no technical distinction between a silencer or muffler and the terms are often used interchangeably. There are generally two types in use for agricultural uses - absorptive and reactive silencers.

Absorptive silencers contain fibrous or porous materials and depend on the absorption properties of these materials to reduce noise. Figure 4 shows an absorptive silencer constructed by a farmer in Ontario.

Reactive silencers depend on the reflection or expansion of sound waves with corresponding self-destruction as the basic noise-reduction mechanism. The most common example is a car muffler. These silencers must be custom designed and tuned to the discrete frequency character of the noise. Reactive silencers are sometimes available from the original manufacturers of grain drying equipment.

Figure 4. Farmer Built Absorptive Silencer.