Construction noise is the product of the machines and processes involved in construction. Since much of construction is carried out outdoors, the external noise effects are much more important than for other kinds of industrial noise.
Regardless of the type of structure under construction, is it a high-rise building, a bridge, a highway or a sewer, the equipment employed can be classified into five major categories:
1. Earthmoving equipment.
2. Materials handling equipment.
3. Stationary equipment.
4. Impact equipment.
5. Other types of equipment.
Figure 18.2 shows noise ranges for typical items of equipment within each of these categories. The noise is clearly quite high, although, with the exception of impact pile drivers, it does not reach the peaks of industrial equipment noise.
Like other kinds of industrial noise, construction noise tends to have more energy in the lower frequency of the spectrum than in the higher ones. However, there are differences among the various types of equipment. For instance, among earthmoving machines, the worst offenders are scraper and dozer units, that expose the operator to excessive noise conditions for many hours a day.
The fact that the levels in Fig. 18.2 are reported at 50 feet from the construction machines suggests that the main EPA concern is with the annoyance of people living nearby. However, it is easy to extrapolate back to the worker’s ear. For every halving of the distance there will be a rise of 6 dB. At 6 feet the levels will be increased by 18 dBA so that the tractors, backhoes and scrapers will produce levels at least as high as 110 dBA.
Although the home is generally a sanctuary from damaging noise, it contains, nevertheless, noise sources with levels above decibels that can damage hearing with sufficient exposure, that is, for many hours a day seven days a week, as well as many other sources that can produce severe annoyance.
There are basically four sources of noise in a household – human-generated noise, appliance noise, building-equipment noise and background noise impinging upon the household from outside. In each of these categories the noise is either airborne noise, such as voices or impact noise, due for instance to the fall of an object, which is then transmitted by the structure of the house and converted to airborne noise through vibrations of components of the structure.
Human-generated noise-voices, dropping of objects, children jumping or even just walking—can be a strong irritant, particularly in dwellings designed with insufficient insulation. Indeed in one survey human noise (voices and children playing) was found to be predominant source of noise even outdoors in a sizable number of cases.
Household appliances generate a broad range of noise, according to the particular type of appliance. The upper limits of the range can reach very high sound levels. The level of exposure of people in other rooms (‘secondary noise’) of the household is, of course, less—as much as 10-20 dBA less—but can continue to reach high levels, particularly for certain penetrating sounds, such as those from a noisy home shop tool.
An important source of household noise, particularly in those households away from the core of the city, is motor-powered gardening appliances. At times gardening involves also the use of chain saws, which are the noisiest of all kinds of gardening equipment, producing some 115 dBA at the user’s ear and some 85 dBA at 50 ft.
Building equipment, similarly, presents a broad range of noises and can reach high peaks. The portion of the noise that reaches the occupants of the building depends on the location of the equipment—whether the occupant’s exposure is direct or indirect and whether the equipment is segregated in acoustically desirable locations the acoustic design of the building (walls, ceilings, floors) and the measures taken to insulate the equipment.
Background noise is determined by the environment of the dwelling. Street and airplane noises are the most common determinants of the background noise, but construction, industrial and human noise (e.g., a school yard or a market) can also be important. Clearly the background noise levels vary with the time of the day and in certain cases can also be seasonal, thus defying simple categorisation.
For instance, background sounds due to traffic or air-conditioners tend to mask interior sounds, but when— they subside—when traffic noise is reduced at night or the air-conditioner is stopped—obnoxious interior sounds become noticeable. The operation of street-cleaning or garbage-collection equipment whose noise levels, although intrinsically quite high, would be acceptable during daytime, becomes intolerable at night or during the early morning hours.
While accepting these temporal variations in background noise, it is clear that, in general, different areas have on the average different background noise.
Many leisure activities have become a major source of noise and a major hazard. Hi-fi sets are among the worst offenders. Rock groups produce about 100 dB at the performer’s ear and more in the front row of listeners. Even children’s pop guns can be dangerous to hearing with one exposure.
In dealing with rock and roll music one must be careful, however, about putting it on a par with noise exposure at work. While it is true that levels of 125 dBA are produced by some famous rock groups and such levels can give rise to hearing damage in the great majority of people exposed to them, this is only true if the exposure is of the order of 1000 hours total.
This could in fact be accumulated by a devoted fan going to one four-hour concert every week for five years, but it must be understood that even if there is lack of awareness of the risk, this is still exposure by choice. The situation of the worker is very different; even if there is awareness, which is unlikely, there is often very little choice about getting a quieter workplace.
Recreational vehicles and craft—motorcycles, snowmobiles, all-terrain vehicles and pleasure boats—which have greatly increased in popularity in recent years, produce noise levels at the user’s ear that are so high as to lead to impairment with prolonged exposure. Indeed the 118 dBA reported for snowmobiles will produce 50 per cent loss of hearing for weak conversational speech in 10 per cent of the exposed people in as little as 5 years if the exposure is a typical 4 hours a day, two days a week, 13 weeks a year.
The noise levels produced are also sufficiently high at 50 ft to severely affect people in the environment of these vehicles. Among recreational vehicles one must include general aviation aircraft which are flown to an increasing degree for pleasure. In their interior their average noise level is around 90 dBA, with peaks as high as 103 dBA.
The sirens used by police, firemen and ambulances serve to communicate an urgent message. Thus, they need to be very intense sources of sound. For example, the sirens of fire trucks in New York City have been observed to emit 124 dBA at 3 ft.
Clearly these high levels of sound have distressing and potentially harmful effects both on the occupants of the vehicle and on the people in the street and in the surrounding buildings. The effect on those in the environment of the vehicle is accentuated by the frequency with which sirens belonging to different urban services are heard.
The remedies are not simple. For the operators of the vehicle, the adoption of earmuffs or the soundproofing of the cabin present the obvious disadvantage that other signals and traffic sounds cannot be heard. For the persons in the environment of the vehicle, to attempt to make the sound less irritating by changing some of its characteristics—for instance by giving the signal a musical quality— may remove much of the urgency of the signal.
An unfortunate and inescapable by-product of the motorisation of agriculture is the increase in the noise level in rural environments. Countryside undisturbed by the noise of engines and motor vehicles is increasingly rare. The principal sources of noise in agricultural applications are primarily tractors, trucks, bulldozers, as well as special purpose machines. These sources are not substantially different in their sound emission characteristics—and hence in their effect on operators and the environment—from those of vehicles and machines used in other occupations.
It is an unfortunate condition of this earth that a large percent of its inhabitants become involved in military activities—as members of the armed forces or as targets, at best, as bystanders. Military activities can generate some of the loudest man-made noise, because of their intrinsic nature and because environmental considerations are by necessity secondary to military ones. However, the internal environment of planes, ships and tanks must be sufficiently quiet so as to reduce fatigue and make voice communication possible.
The sources of military noise are basically four:
1. Explosions (from firearms, artillery, bombs, rockets and construction activities).
2. Airplanes and rockets.
3. Engines (in combat vehicles, in other vehicles, as well as in ships).
4. Other equipment (generators, etc.).
In the case of large explosions and rockets, a single event is often sufficient to permanently impair hearing. Even the explosions from portable firearms can have that effect—and repeated exposure in any case is likely to do so. The other sources of military noise are basically not different from corresponding sources in non-military activities—except that they are often louder and that less effort are made to shelter both operators and environment from their long range effects.