industrial hygiene assessment of a light manufacturing

Forensic Applications Consulting Technologies, Inc.

185 Bounty Hunter’s Lane, Bailey, Colorado 80421

Phone: 303-903-7494 http://www.forensic-applications.com

Industrial Hygiene Assessment

Of A Light Manufacturing Facility

Airborne Metals and Sound Survey

Xxxxxx Xxxxx Xxxx

Xxxxxx Xxxxx Xxxx XXXX Xxxx Xxxx Street Thornton, CO XXXXX

Prepared for:

Xxx Xxx Xxxxxx Xxxxx Xxxx

XXXX Xxxx Xxxx Street Denver, CO XXXXX

Prepared by:

Forensic Applications Consulting Technologies, Inc.

185 Bounty Hunter’s Lane Bailey, CO 80421

November 9, 2009

Industrial Hygiene Assessment FACTs, Inc. of 15 Xxxxxx Xxxxx Xxxx, Thornton CO

EXECUTIVE SUMMARY On Tuesday, October 27, 2009 personnel from Forensic Applications Consulting

Technologies, Inc. (FACTs) performed an employee exposure assessment to

welding fumes and sound at the Xxxxxx Xxxxx Xxxx facility located at XXXX

Xxxx Xxxx Street, Denver, CO XXXX.

Results of the sound monitoring indicated that while most of the shop floor had

exposures below the Action Level, activities in the Router Area had an high

probability of consistently exceeding the OSHA Permissible Exposure Limit

(100% Dose) to an unprotected worker. However, the hearing protection devices,

used by the employees, when worn diligently, will afford adequate protection.

o Nevertheless, Xxxxxx Xxxxx Xxxx must either administer a continuing,

effective hearing conservation program, as described in paragraphs (c)

through (o) of Title 29 Part 1910.95 for the two Router Area employees,

or reduce the employee exposures to less than an 50% dose through

engineering or administrative controls.

o Two exterior operations similarly posed a significant sound exposure,

however, the use-cycles are such that an excess of a 50% dose would not

reasonably occur. Nevertheless, the standard practice of employees

wearing hearing protection devices while engaged in these operations

should be strongly .

Full shift air monitoring for welding fume contaminants indicated that on the day

of our assessment, exposures to metals associated with welding byproducts was

below the Equivalent Mixture (EM) for the metals identified. Based on our

observations and the results, it is unlikely that conditions would exist in the

welding shop wherein exposures would exceed the PEL for any of the metals or

the EM for the constituent metals.

EMPLOYEE EXPOSURE ASSESSMENTS

Conditions

The assessment began at 8:00a.m. and progressed until the end of shift at 4:30 p.m. On

the day of our visit, the weather was seasonably cold. The barometric pressure was 24.6

inches of mercury (625 mm Hg) and a slight cold breeze was blowing from the west.

According to the management and the working staff whom we interviewed, the

occupancy and level of production and activity in the manufacturing facility was

“normal” and a good representation of daily activity. For the purposes of our

assessments, we asked the staff to engage in additional duties and operate rarely used

equipment to assist us in developing a “worst case” scenario.


Sound Monitoring

Regulations

For the purposes of Xxxxxx Xxxxx Xxxx, OSHA regulates noise exposure under Title 29

of the Code of Federal Regulation (CFR) Part §1910.95, Occupational noise exposure.

This standard requires that employee exposure to occupational noise be determined and,

if necessary, controlled through engineering controls, administrative controls or personal

protection equipment.

According to OSHA §1910.95(d) (1), when the employer has information which

indicates that an employee exposure may equal or exceed an 8-hour time-weighted

average of 85 decibels (equivalent to a 50% dose), the employer must develop and

implement an hearing conservation program. The elements of a hearing conservation

program include yearly audiometric testing, training, and the provision of adequate

protection devices.

When employees are subjected to sound exceeding a dose of 100%, feasible

administrative or engineering controls must be utilized. If such controls fail to reduce

the sound exposures below a 100% dose, personal protective equipment must be provided

and used to reduce sound levels.

The strategy of sound monitoring should be capable of identifying employees (if any)

who need to be included in the hearing conservation program and to enable the employer

to select the proper hearing protectors. According to OSHA, a survey should include all

continuous, intermittent and impulsive sound levels from 80 dB to 130 dB.

There are different "weightings" given to the way sound pressure levels (SPLs) are

measured. The "A" weighting most closely resembles the way the human ear responds to

sound. Therefore, the A weighting is the closest representation of continuous SPLs

injurious to the ear. For this reason, OSHA requires that, at a minimum, all sound

surveys are conducted using the A weighting scale.

Data from the C weighting SPLs was also evaluated during our assessment to

qualitatively determine the equivalent A weighting employee exposure to sound when the

employee is wearing hearing protection.

OSHA arbitrarily follows the so-called "5 dBA doubling rule." This means that for every

increase of 5 dBA, the legally permitted time of exposure over 85 dBA is halved. Thus,

85 dBA for 480 minutes; 90 dBA for 240 minutes; 95 dBA for 120 minutes; and 100

dBA for 60 minutes all equal a 50% dose.

In reality, the SPL roughly doubles with every 3 dB increase, therefore, FACTs

recommends following a 3 dB doubling rule to better approximate the potential hazard

associated with the sound. Indeed, most other countries and the International Labour

Organization has implemented such a rule.


Using the 5 dB doubling rule, OSHA has promulgated various acceptable noise levels.

The first is the Permissible Exposure Limit (PEL) which for continuous noise is 90 dBA

for an eight hour day. This means an unprotected employee would receive a 100% dose

when exposed to 90 dBA for an eight hour period.

The OSHA Action Level is 85 dBA, or a 50% dose. An employee exposed to 90 dBA,

would receive a 50% dose in 4 hours. An employee exposed to 85 dBA, would receive a

50% dose in 8 hours. Dose is calculated by OSHA (and MSHA) as follows:

Dose

100

5

*Length of shift in hours

8

2

SPL-90

When the Action Level has been reached or exceeded, an hearing conservation program

(HCP) must be implemented for the exposed employees. Hearing protection devices

(HPDs) must be made available (although use is optional), and training must be provided

to those employees who wish to use the HPDs.

In a work-place which has employees exposed to SPLs greater than the Action Level, the

occupational noise exposure standard must be posted. Any employee who has been

exposed to a SPL of greater than a 50% dose must be informed of these results.

Employees with normal hearing who are exposed at or above the PEL or a 100% dose are

required to wear HPDs which are capable of attenuating the noise to no greater than 90

dBA or a 100% dose. Employees who have experienced a “standard threshold shift,” as

determined by a physician or other health professional, and are exposed to the PEL or a

100% dose are required to wear HPDs which are capable of attenuating the noise to no

greater than 85 dBA or a 50% dose.

Methodology

The objectives of the sound survey were:

· to determine worse case noise levels for selected areas throughout the plant

· to anticipate 8 hour exposures for selected areas throughout the plant

· to anticipate the worse case exposures for selected processes in the plant

· to determine which employees may be at risk from elevated noise levels

· to satisfy the intent of the OSHA definition of an adequate sound survey

The survey was conducted during a level of production and activity that is typical of the

plant, and at the request of FACTs personnel, employees were asked to perform

additional duties so that various pieces of equipment could be assessed. Production was

normal to high and all normal equipment was in use.


At each sampling point, we typically measured:

1) dBA, SLOW and PEAK response

2) dBC, SLOW and PEAK response

3) Spectral sound analysis

Although many of the wave forms we observed had asymmetrical amplitudes, none of the

equipment or processes we observed appeared to have a significant IMPACT/IMPULSE

component, and no further discussion is given to that noise component.

INSTRUMENTATION

During our survey, we used a Quest Technologies 2900 SLM with the detachable OB100

spectral sound analyzer. The instrument was factory calibrated on February 14, 2009 and

the next scheduled factory calibration is due on the same date 2010. Additionally, the

meter was subjected to a pre-use and post-use field calibration by FACTs at the facility

on the day of our visit with a Quest QC 10. The response of the instrument was

satisfactory and no adjustments were made to the SLM during pre-calibrations. The

sound generator used for field calibration at the facility is traceable to the National

Institute of Standards and Technology.

The calibration logs, archived at the corporate offices of FACTs, provide the expected

response of an SLM subjected to an SPL of 114 dB. During the initial calibration

process, the SLM was not adjusted for altitude since the readings were within accepted

tolerances.

The SLM was an ANSI Type 1, high precision sound level meter and spectral sound

analyzer. To minimize directional sound, we used a random incident microphone. Due

to the slight breeze outside, during our exterior work, we employed a windsock.

The SLM was capable of recording SPLs from 30 to 140 dB on A, B, C and FLAT (also

called “linear”) weightings. The instrument has true PEAK (35 millisecond), FAST

(0.125 second) and SLOW (1 second) time constants. Maximum root mean square (rms)

and "capture" rms SPL measurements were collected during the survey. The instrument

has band passes at the international centers of frequency from 31.5 Hz to 16 kHz.

Due to the dynamics of sound, SLM readings are traditionally considered to be

representative of the sound environment plus or minus 3 dB.

The sound environment at Xxxxxx Xxxxx Xxxx is typical for most industrial settings in

that it has sounds which are comprised of complex mixtures of waveforms. Many of the

constituent sounds may be injurious to health, but their significance may be diminished

using the OSHA mandated SLOW time constant.

These complex waveforms are termed "spiky" waveforms. Such waveforms can be more

accurately measured using the PEAK time constant which will process spiky waveforms


differently than the SLOW setting. The difference between the PEAK dBA and the

SLOW dBA is called the "crest factor" and can be 10 to 20 dB. We believe that the use

of the dBA PEAK helps to augment the OSHA mandated dBA SLOW measurements and

is a more accurate representation of the employees’ exposure to injurious noise.

Although Xxxxxx Xxxxx Xxxx is only required to use the dBA SLOW value, the dBA

PEAK value is the worst-case value and we used dBA PEAK for determining employee

exposures and calculating dose. As such, although personal dosimetery would still result

in greater than a 100% Dose in the router area, personal dosimetery results would

indicate lower exposures than reported here.

HEARING PROTECTION DEVICES

Xxxxxx Xxxx requires its employees to wear hearing protection devices in various

manufacturing areas. During this survey, we determined the effectiveness of the hearing

protection devices (HPDs) which are used at the facility. Based on our observations,

there are two primary HPDs used: "Mold-X Spark Plugs" and a “Peltor muff.”

Each HPD, has a noise reduction rating (NRR) which is established by the U.S. EPA

under 40 CFR §211.201. The NRR is a rating which speaks to the issue of how well the

HPD might protect the employee (not necessarily how well the employee will be

protected).

The Mold-X plugs have a listed NRR of 33. Although the box for the Peltor muffs was

not available, the muffs were visually identical to the Peltor “Muff H7A Optime 101”

product. The Peltor Optime 101 is listed by the manufacturer as having a NRR of 27.

A qualitative method of determining employee protection may be used in the absence of

spectral analysis of the sound. The qualitative method assumes that the noise is "pink

noise," and subtracts the NRR from the dBC to determine dBA exposure as follows:

Employees' Exposure in dBA = (dBC - NRR)

This method is qualitative at best, but is useful when no spectral information on the sound

is available. The C weighted SPL values which we measured at the facility may be used

for qualitatively determining the adequacy of any HPD in any particular area using the

manufacturer’s NRR; which is listed on the shipping container for the HPD.

In reality, each HPD attenuates different frequencies differently, and especially where the

noise is from a rotating device such as the routers and radial saws used at the facility;

since these noise sources often have pure tone pitches associated with them centered at

specific frequencies.

To more accurately determine an employee's exposure to noise while wearing a particular

HPD, the spectral components of the noise should be measured. The ability of the HPD

to attenuate each frequency center or octave should then be assessed. To determine HPD


efficacy during this survey, we used the method found in 40 CFR §211.207 which is

essentially the same as the “NIOSH Method #1” referenced by OSHA in their noise

exposure standard (Appendix A of 29 CFR §1910.95).

The method uses the manufacturer’s information on the HPD's ability to attenuate

specific frequencies centers and it also incorporates specific uncertainties associated with

the HPD's manufacturer's assessment of the attenuation. Finally, the method provides an

overall assessment of the HPD's protection in the specific noise environment in question.

We have calculated the HPD Protection Factor for the router and saws. This protection

factor is defined as that estimated protection for 98% of the users of the particular HPD

exposed to that particular mixture of noises (that particular area or process). The "HPD

Protection Factor" is applicable assuming the employee wears the HPD in a conscientious

manner as specified by the manufacturer.

Router Area

General and specific sound monitoring was performed in this area which contains two

identical routers and one radial saw. General monitoring was performed to determine the

contribution of sound from air compressor, air hose as well as the two units running

simultaneously.

Router Assessment

Employees informed us they would not normally perform work on more than 100 PVC

rails or posts per day. The 100 units per day was described as a worst case scenario. The

cycle time for a single router is: Loading time 20 seconds, on-time 60 seconds, off-time

10 seconds, loading time 20 seconds. The “on-time” represents the only significant noise

exposure. 100 rails or posts on one router would represent an higher noise exposure than

50 rails or posts being processed simultaneously on two routers.

Our noise measurements were made with both routers running, each manned by a

separate employee.

The table below provides the pertinent noise information. The SPLs listed are valid for

up to one meter from the router and should be considered valid for the entire router area

(from the north wall out to the main aisle).

dBA

PEAK dBC

PEAK Significant Frequency Centers

(all dB are FLAT) Dose Posed

Estimated TWA

106 100 500 Hz 1 kHz 2 kHz

191% 95 dBA 94 97 94

Table 1 SPLs for the Router Area


The effective attenuation of the Mold-X Spark Plugs, which are listed as NRR 33 is in

fact 39 for this sound component. The Employee’s protected TWA exposure while

working in the area and diligently wearing the Mold-X Spark Plugs is 67 dBA.

The effective attenuation of the Peltor Muff H7A which is listed as NRR 27 is in fact 38

for this noise profile. The Employee’s protected TWA exposure while working in the

area and diligently wearing the Peltor Muff is 68 dBA.

Radial Saw

The radial saw used in the router area is not used on a daily basis. During the summer,

the saw may be used up to four hours per day. During the remainder of the year, the

employees informed us that they would rarely use the radial saw more than twice each

week.

The maximum time at the saw would occur during the summer and may approach a

maximum of four hours per day. The operation use cycle is 25% “on” and 75% “off.”

The table below provides the pertinent noise information for the radial saw during

maximum use. The SPLs listed are valid for up to one meter from the saw.

dBA

PEAK dBC



Estimated TWA

102 102 1 kHz 2 kHz 8 kHz 16 kHz

66% 87 dBA 90 91 99 96

Table 2 SPLs for the Radial Saw in the Router Area

If one employee was operating the router at maximum production, and one employee was

operating the radial saw during maximum production the estimated unprotected TWA for

each would be 97 dBA.

The effective attenuation of the Mold-X Spark Plugs which is listed as NRR 33 is in fact

39 for the radial saw noise profile. The Employee’s protected TWA exposure while

working in the area and diligently wearing the Mold-X Spark Plugs is 63 dBA.

The effective attenuation of the Peltor Muff H7A which is listed as NRR 27 is in fact 34

for this noise profile. The Employee’s protected TWA exposure while working in the

area and diligently wearing the Peltor Muff is 69 dBA.

If one employee was operating the router at maximum production, and one employee was

operating the radial saw during maximum production the estimated protected TWA for

each would be approximately 4 dBA greater than the two values listed above.

Air Compressor

The air compressor in the router area does not significantly contribute to the employee’s

exposure profile.


Air Hose

The air hose in the router area does not significantly contribute to the employee’s

exposure profile. The air hose has a significant frequency center at 8kHz (88 dB FLAT)

as measured from 5 cm.

Welding Shop

The welding shop has a low ambient noise exposure profile and contains two machines

with an higher potential for employee noise exposure. The most significant noise source

is the stereo in the shop.

Ambient Welding Shop

The highest measured SPLs in the welding area were 81 dBA (83dBC) with no

significant pure tone pitches. The majority of the pink noise is from the stereo

equipment. The dBC is higher than the dBA due to a low frequency profile contribution

from the two large axial ventilation fans in the welding shop.

We cannot reasonably foresee a dose exceeding 50% unless the stereo equipment volume

is set at an unacceptably high level.

Nash Machine

The Nash Machine is a rarely used piece of equipment which chops a small piece of

metal from the end of a pipe. The device is used occasionally and perhaps as often as ten

times per day. The use cycle is approximately four seconds. The machine has a

maximum FLAT PEAK of 83 dB.

Pipe Cutter

The pipe cutter in the welding shop is infrequently used, and when used, is used a

maximum of 20 times per day, with an exposure cycle of one second per use. The pipe

cutter has a FLAT PEAK SPL of 99 dB. The TWA contribution of the pipe cutter is

approximately 49 dBA (cumulative dose contribution 0.4% using 30 CFR Part 62, Table

62-1).

Outside Covered Area

The outside area has three significant noise exposure operations: 1) a radial arm saw, 2)

a mobile chop saw, and 3) a large pipe cutter. None of this equipment is routinely used.

At the request of FACTs, Xxxxxx Xxxxxx employees operated the equipment for the

purposes of exposure assessment.

Chop Saw

During our assessment employees operated a mobile chop saw. The chop saw is used

routinely only one or two days in the autumn for the destruction of fabricated items that

are to be recycled. When it is used, it is used for no greater than one hour, and is


operated by two employees from the welding shop. The saw has a use cycle of four cuts

per minute, three seconds per cut, followed by a one minute reloading time.

The table below provides the pertinent noise information for the chop saw during

maximum use. The SPLs listed are valid for up to one meter from the saw. During the

chop saw operation, other employees are not regularly within two meters of the saw.

dBA

PEAK dBC



Estimated TWA

103 102 1 kHz 4 kHz 8 kHz 16 kHz

8% 71 dBA 93 98 105 99

Table 3 SPLs for the Outdoor Chop Saw

The saw has an asymmetrical wave pressure profile wherein there is a FLAT PEAK of

106 dB lasting a fraction of a second, followed by a steady 103 dBA SLOW for the

remaining approximately 2.5 seconds. During our assessment, the employees were

wearing the Mold-X Spark Plug ear plugs.

The effective attenuation of the Mold-X Spark Plugs which is listed as NRR 33 is in fact

40 for this noise profile. The Employee’s protected TWA exposure while working in the

area of the chop saw during a high production day and diligently wearing the Mold-X

Spark Plugs would be 67 dBA.

Radial Arm Saw and Exterior Pipe Cutter

The exterior radial arm saw and exterior pipe cutter are very rarely used pieces of

equipment. We were informed that the equipment may be used a few times each year,

and that when the equipment is used, it is use for only a matter of moments.

The Radial Arm saw has a FLAT PEAK of 96 dB. The pipe cutter has an SPL of 92 dBA

PEAK (and roughly 92 dBA SLOW); and 93 dBC (SLOW). The pipe cutter also has

significant frequency centers at 500 Hz (92 dB FLAT), 1 kHz (93 dB FLAT), and 2 kHz

(90 dB FLAT).

The use of each of these machines, in the manner described by the employees would not

contribute greater than 2% of cumulative dose (less than 58 dBA SLOW TWA).

Air Monitoring

Occupational Standards

OSHA

Currently, the OSHA regulates the various metals in welding fume. Standard practice is

to determine which metals are present and then compare the exposures of each of the

metals against the Permissible Exposure Limit (PEL) for that metal, and express the value


as a fraction of the PEL. By summing the fractions, one can express an “Equivalent

mixture” (EM) of the mix of contaminants. Using the EM applies specifically when the

contaminants are toxicologically similar. In this case, FACTs has used the EM not to

imply that the individual metals are in fact toxicologically similar, but as a way of

presenting a worst case scenario of the employee exposures.

The levels of permitted exposures are found in the so-called Z-Tables in Title 29 of the

Code of Federal Regulations (29 CFR), Part 1910 Section 1000 (§1910.1000 (z)).

Methodologies

Full shift samples were collected and analyzed for airborne metals according to the

NIOSH 7300 Method. The samples were submitted to Reservoir Environmental

Laboratory in Denver. Reservoir is accredited by the American Industrial Hygiene

Association as being proficient in performing this type of analysis.

Traditionally, FACTs has corrected air volumes for Denver’s altitude and used the NTP

equivalent. However, in light of recent philosophical changes being adopted by the

international scientific community1 in data interpretation as supported by various

publications,2 FACTs has not corrected the air volumes to NTP.

For each sampling and analytical method there is a degree of uncertainty associated with

the reported values. When an Industrial Hygienist receives a laboratory report, he will

usually calculate the upper confidence interval UCL95 and report that value, to help

achieve a worst case scenario. In this case, however, the exposures we observed at

Xxxxxx Xxxxx Xxxx are so low, even reporting the UCL95 values will not significantly

alter the compliance ramifications of the samples.

Generally, the geometric standard deviation of interday and intraday airborne

concentrations lie between 1.2 and 2.5 geometric standard deviations.3 This means that

the values reported here should not be viewed as absolute truth, but rather a “snapshot” of

employee exposures. Although the sampling we performed demonstrated that the

exposures were compliant on the day the sampling occurred, we recommend that ongoing

sampling take place quarterly for at least two years, to develop sufficient data to better

understand the interday variations of exposures at Xxxxxx Xxxx.

Samples were collected from three employees who work in the welding shop, which

includes the fabrication section. Two employees were full time welders and one

employee was a full time fabricator. The personal pump worn by the Fabricator failed

1 ASTM International D22 Committee on Indoor Air Quality

2 Stephenson DJ; Lillquist DR, The effects of temperature and pressure on airborne exposure

concentrations when performing compliance evaluations using ACGIH TLVs and OSHA PELs. Appl

Occup Environ Hyg 16(4): 482-486 (2001).

3 NIOSH Occupational Exposure Sampling Strategy Manual, HEW Publication Number 77-173 (1977)


after 291 minutes. However, the Fabricator worked in the same areas the welders, and

the primary exposure to the fabricators is from the welders. Therefore, there is no loss in

significant data, and the data still meet the data quality objectives, when viewed in the

context of the remaining two samples.

In the table below, we have presented the results of the air monitoring. The data have

been censored to the extent that only the metals observed above the method detection

limit have been reported. The samples were also analyzed for arsenic, beryllium,

cadmium, cobalt, chromium, magnesium, molybdenum, nickel, lead, and vanadium.

However, each of the above metals were not present in detectable concentrations and are

not discussed further.

Each personal pump was calibrated prior to and immediately after use in a manner

consistent with good industrial hygiene practices and procedures and NIOSH protocols.

With the exception of the failed pump, neither of the remaining two pumps exhibited a

RPD of greater than 1% between pre and post calibrations.

The type of pumps FACTs used for our assessment automatically records how long the

pump has been running and will automatically shut down when an internal calibration

reference identifies a flow fault that deviates greater than 5% of the set flow rate. This

prevents a “trailing off” effect of air flow through the sampling cassette and allows the

industrial hygienist to calculate a sample volume with good confidence.

It is for this reason, FACTs is able to report a sample result for the sample whose pump

failed after 291 minutes (Sample CM102709-02). For the purposes of calculating a time

weighted average, FACTs assumed that the exposures during the first 291 minutes were

similar to the exposures during the remaining 189 minutes of the employee’s shift (an

assumption that is borne out as reasonable based on our observations).


.

Sample Al Cu Fe Mn Zn

EM mg/m3 PEL %PEL mg/m3 PEL %PEL mg/m3 PEL %PEL mg/m3 PEL %PEL mg/m3 PEL %PEL

CM102709-01 0.005 5 0.1 0.005 0.1 5.0 0.27 10 2.7 0.044 5 0.9 0.41 5 8.2 0.17

CM102709-02 0.004 5 0.1 <0.004 0.1 <4.0 0.061 10 0.6 <0.04 5 <0.8 0.06 5 1.2 0.02

CM102709-03 0.005 5 0.1 0.011 0.1 11 0.45 10 4.5 0.09 5 1.8 0.95 5 18.9 0.36

Table 4 Results of Personal Air Monitoring in the Welding Shop

Sample Employee Position/Function Start Stop Total Minutes Volume

(uncorrected l)

CM102709-01 Xxxx Xxxx Welder 07:58 16:28 510 1,045

CM102709-02 Xxxx Xxxx Fabricator 08:10 13:01 291 582

CM102709-03 Xxxx Xxxx Welder 08:21 16:27 486 996

Table 5 Air Monitoring in the Welding Shop

During the shift, Welder Xxxx Xxxx and Welder Xxxx Xxxx both wore 3M elastomeric P100 Model 2097 half face APRs.


CONCLUSIONS Employee exposures to airborne contaminants in the Welding Shop (or elsewhere) are not

reasonably likely to exceed the OSHA PEL. Objective samples were collected during

normal operations

Sound exposures to employees in the Router Area (from the north wall to the main aisle),

will confidently exceed the OSHA Action Level during normal activities at the facility.

Engineering controls may be feasible by building simple small enclosures around the

router jig table. The enclosures could have open ends for moving work pieces quickly in

and out of the jig. The entire enclosure could be hinged to permit quick access to the jig

table.

Engineering Controls

To design an effective enclosure for dampening sound, two concepts should be

considered: "noise reduction" and "transmission loss." Noise reduction is the difference

in SPL measured inside and outside an enclosure and is dependent on the sound

environments on both sides of the enclosure. Transmission loss is independent of the

sound environment, and is the reduction in energy transmitted through a material.

Transmission loss is a function of mass and will typically increase five to six dB for each

doubling of partition weight per unit surface area (for a particular frequency), or for each

doubling in frequency. Which is why it is easier to mitigate the higher frequencies, and

lower frequencies are more difficult to control. Fortunately, for the routers, the sound

frequencies of concern are in the higher ranges, and therefore, easier to control with

“home-made” enclosures.

For this facility reverberation (known as "room constant") is not an issue.

Absorption of sound by a surface will depend on the material from which the surface is

made and with what the surface is covered . The “absorption coefficient” is a

dimensionless unit representing the fraction of energy absorbed on the surface. For the

enclosures, Xxxxxx Xxxx may find that ¾ inch plywood enclosures lined with “egg

carton” foam or shag carpeting may adequately reduce noise exposures to below 50%

dose.

The minimal costs associated with engineering controls is greatly off- set by the costs of

developing and administrating an hearing conservation program.

Regulatory Requirements

According to OSHA 29CFR §1910.1020 (Access to employee exposure and medical

records) all employees affected by these data (whether directly monitored or not) are

permitted access to this information without restriction. According to the standard, all

employees must be informed of the existence of this information, must be informed of the


name of the person who maintains this information, and must be informed of the method

for requesting this information.

All raw data (calibration forms, field sampling forms, photographs, etc.) are archived at

the corporate offices of FACTs and will be made available to Xxxxxx Xxxxx Xxxx, or

other authorized personnel upon request.

We hope the information provided has been useful and timely. Please do not hesitate to

contact us with questions.

Caoimhín P. Connell

Forensic Industrial Hygienist

industrial hygiene assessment of a light manufacturing

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