The importance of proper safety training cannot be emphasized enough. If an emergency should arise, sampling personnel must be able to determine the cause of the accident and be prepared to act accordingly. Far too often, the rescuer, because of inadequate preparation, becomes another victim. Safety procedures should become routine, and the best way to accomplish this is through continuous training. Training in the following areas should be provided to all employees required to work in confined space or with a team that performs work in a confined space:
- Cardiopulmonary resuscitation and basic first aid
- Use of applicable safety equipment
- Confined space entry procedures
Entry and exit procedures include the following steps:
- Identification – Sampling personnel must be able to identify the potential hazards associated with inspections and sampling. Training should emphasize the possible results of improper safety procedures.
- Testing – All confined spaces must be tested prior to entry.
- Evaluation – Tests must be evaluated for oxygen level, explosivity, and potentially toxic substances. Sampling and working personnel should also consider necessary safety equipment.
- Monitoring – The atmosphere in a confined space is subject to change. Therefore, the area should be continuously monitored during the sampling and other activities.
Rescue procedures must be developed for each type of confined space that may be encountered by the sampling personnel. A written record of training and safety drills should be kept. Rescue procedures should be practiced frequently enough to ensure proficiency in any necessary rescue situations. In developing a successful training program, the industry is encouraged to call on other agencies (e.g. local fire and rescue department) with expertise in any of the areas described above.
Also, a summary of chemical and allied industrial plant hygiene method are given in Table E.1.
Noise
Noise, commonly defined as unwanted sound, is an environmental phenomenon to which we are exposed before birth and throughout life. Noise is considered as an environmental pollutant, a waste product generated in conjunction with various anthropogenic activities. Noise is any sound – independent of loudness – that can produce an undesired physiological or psychological effect in an individual and that may interfere with the social ends of an individual or group. These social ends include all of our activities – communication, work, rest, recreation, and sleep.
Occupational Noise Exposure
Noise, or unwanted sound, is one of the most pervasive occupational health problems. It is also a by‐product of many industrial processes. Sound consists of pressure changes in a medium (usually air), caused by vibration or turbulence. These pressure changes produce waves emanating away from turbulence or vibrating source. Exposure to high levels of noise causes hearing loss and may cause other harmful health effects as well. The extent of damage depends primarily on the intensity of the noise and the duration of the exposure. Noise‐induced hearing loss can be temporary or permanent. Temporary hearing loss results from short‐term exposure to noise, with normal hearing returning after a period of rest. Generally, prolonged exposure to high‐noise levels over a period of time gradually causes permanent damage. OSHA’s hearing conservation program is designed to protect workers with significant occupational noise exposures from hearing impairment even if they are subject to such noise exposures over their entire working lifetimes.
Basics of Occupational Noise and Hearing Protection
An estimated 25 million Americans – many of whom are workers – are exposed to noise that poses a threat to their hearing. Everyone at some time or another has experienced the effects of noise pollution. Many people are unaware that the sounds that cause them so much serious health threats are a result of noise pollution. Noise pollution is traditionally not placed among the top environmental problems facing the nation; however, it is one of the more frequently encountered sources of pollution in everyday life. Noise is typically thought of as a nuisance rather than a source of pollution. This is due in part because noise does not leave a visible impact on the environment as do other sources of pollution.
The damage done by the traditional pollution of air and water is widely recognized. The evidence is right before one’s eyes – in contaminated water, algae bloom, oil spills, and dying fish, as well as in smog that burns the eyes and sears the lungs. However, noise is more subtle pollutant. It is estimated over 20 million Americans are exposed to dangerous noise levels without knowing it from trucks, airplanes, motorcycles, stereos, lawnmowers, and kitchen appliances. Sound travels in waves through the air like waves through water. The higher the wave, the greater its power. The greater the number of waves a sound has, the greater is its frequency and pitch.
The strength of sound or sound level is measured in decibels (dB). The decibel scale ranges from 0, which is regarded as the threshold of hearing for normal, healthy ears, to 94, which is regarded as the theoretical maximum for pure tones. Since the decibel scale, like the pH scale, is logarithmic, 20 dB is 100 times louder than 0; 30 dB is 1 000 times louder; 40 dB is 10 000 time louder, etc. Thus at high levels, even a small reduction in level values can make a significant difference in noise intensity.
Noise: Physical Principles
The frequency of sound refers to the rate at which a complete cycle of high‐ and low‐pressure regions is produced by the source. This is measured in hertz (Hz): 1 Hz is one complete cycle per second. The range of audible frequencies for a young person is from 20 Hz to 20 KHz. As a person age or is exposed to excessive noise, the ability to hear the higher frequencies is reduced. Older adults may have an effective cutoff of 10 KHz or less.
The sound intensity (I) is the average rate at which sound energy is transmitted through a unit area normal to the direction of sound propagation. It is expressed as an energy fluency rate, normally in terms of decibels. The decibel has been defined as 10−12 W/m2. Sound intensity is a function of the sound power (P) of the source. The relationship of sound intensity to sound power is given by
Sound power should not be confused with sound pressure (p). Sound pressure refers to the root mean square (rms) value of the pressure changes above ambient atmospheric level produced by a sound source. It is typically measured in units of Pascal, Newton per square meter (N/m2) or dB. The dB, as used for sound pressure, is referred to 20 μPa or 2 × 10−5 N/m2, which is considered the threshold of hearing for normal person. The range of sound pressures encountered in everyday life is quite broad. Representative levels are shown in Table 5.12.
It is measured by a sound meter level instrument, sound pressure level (SPL), Lp, is characterized in units of dB and is expressed in dB.
(5.13)
where p is the measured rms sound pressure and p0 is the reference value, 0.000 02 N/m2.
The relationship between sound intensity I and sound reference intensity is
The reference intensity, I0, is 10−12 W/m2.
Table 5.12 Representative sound pressure levels.
| Activity | dB | N/m2 | Watts |
| Maximum perception level | 1 | 0.000 02 | 10−12 |
| Night, quiet rural location | 20 | 0.000 2 | 10−10 |
| Quiet room | 40 | 0.002 | 10−8 |
| Normal conversation (3 ft) | 60 | 0.02 | 10−6 |
| Heavy vehicular freeway traffic (automobiles, 50 ft) | 80 | 0.20 | 10−4 |
| Inside helicopter | 90 | 0.70 | 10−3 |
| Power lawn mower | 95 | 1.0 | 0.04 |
| Jet aircraft | 110 | 7.0 | 0.10 |
| Pain threshold | 120 | 20 | 1.0 |
EXAMPLE 5.15 SOUND PRESSURE/INTENSITY RELATIONSHIP
A new noise source with a sound level of 83 dB is installed in a plant with background noise level of 75 dB. Will the combined level exceed the 8‐hour day duration TLV for noise?
SOLUTION
The ACGIH guide gives the 8‐hour noise TLV as 85 dB. The calculation can be done by using Eq. (5.14).
L = log(I/I0) dB; the reference value I0 = 10−12 W/m2 (Table 5.12) and calculating pressure from the new source
Taking antilog and rearranging gives I = 2 × 108 × 10−12 = 2 × 10−4.
Performing the same operation for the background SPL gives
- 75 = 10 log(I/10−12)
- 3.2 × 107 × 10−12 = I; therefore, I = 3.2 × 10−5.
Adding the two sound intensities gives 2 × 10−4 + 0.32 × 10−4 = 2.32 × 10−4 which can then be used to determine the combined SLP.L = 10 log(2.32 × 10−4/10−12) = 10 log(2.32 × 108) = 10 × 8.37 = 83.7 dB (average) which is less than 85 dB (average) TLV limit.
Noise Exposure and Noise Protection
For continuous exposure to noise over an 8‐hour day, OSHA has a set limit of 90 dB average as an 8‐hour TWA. Employers are required to provide a hearing conservation program, noise monitoring, annual audiograms, and hearing protection for employees whose average daily 8‐hour exposure exceeds 85 dBA. Higher levels are permitted for shorter intervals; a 5 dBA increase is allowed up to a limit of 115 dBA for each half of exposure time (0.4 h/15 min). Thus, 95 dBA would be permitted for 4 h/day, 100 dBA for 2 hours, and so on. In general, noise levels above 85 dBA make telephone use impossible and voice communication very difficult and limited, requiring shouting at a distance of only 2 to 3 ft.
Employers must provide hearing protectors to all workers exposed to 8‐hour TWA noise level of 85 dB or above. This requirement ensures that employees have access to protectors before they experience any hearing loss:
- For any period exceeding 6 months from the time they are first exposed to 8‐hour TWA noise levels of 85 dB or above until they receive their baseline audiograms.
- If they have incurred standard threshold shifts that demonstrate they are susceptible to noise.
- If they are exposed to noise over the permissible exposure limit of 90 dB over an 8‐hour TWA.
EXAMPLE 5.16 NOISE EXPOSURE
A worker is exposed to a noise level of 94 dBA for 30 minutes and to 88 dBA for 3 hours each day. Does this exposure exceed the TLV for noise?
SOLUTION
The TLV for 94 dBA noise is 1 hour.
The TLV for 85 dBA is 4 hours.
The combined noise TLV can be expressed by
For exposure of two noise levels,
which is greater than 1; therefore, the TLV is exceeded.
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