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JPA
Certified Industrial Hygienist
(crH)
Jeff Pothast & Assoc., Inc.
13595 W. Exposition Dr.
Lakewood, CO 80228
303.278.4400 phone
303.9f9.1598 mobile
ieff@ieffpothast.com
www.ieffpothast.com
August 19,2023
John Plano
Garfield County
Chief Building Official
108 8th St., Suite 401
Glenwood Springs, CO 81601
RE: Concrete Manufacturing Within a F'abric Enclosure - Protection of Worker
Exposure to Airborne Toxicants
Dear Mr. Plano:
Your concerns about the safety and health aspects of a concrete batch plant within a
fabric enclosure begin with looking at the OSHA Silica Emphasis Program (SEP).
Crystalline silica has an 8-hour time weighted average (TWA) exposure limit of 50
micrograms per cubic meter in air as measured as the respirable fraction of the dust. This
concentration, while toxic via inhalation, is extremely low. So low that you can't see that
amount suspended in air.
Overexposure to crystalline silica (quartz) canresult in interstitial lung disease which is a
non-reversible and disabling disease resulting in fibrosis (scaring) of the deep lung
alveoli, which are responsible for oxygen transport. The disease (silicosis) is well known,
and prevention of exposure includes using a wet process to minimize dust or exhaust
ventilation with adequate capture to remove the particulates from the workers breathing
zone. Adequate exhaust ventilation (OSHA 29 CFR 1910.94) discusses the use of exhaust
ventilation to protect workers from exposure to toxic dusts which requires that there be
adequate capture velocity to move the silica laden dust into the exhaust intake and away
from the worker. Silicosis is likely the oldest recognized occupational disease. Secondary
protection includes proper respiratory protection as prescribed by OSHA in 29 CFR
1910.134. OSHA requires that engineering controls be the primary method of controlling
exposure to employees.
C:\Users\jplano\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook\3PUEB3GK\1601 Garfield
County - Fabric Enclosure for Concrete Processing (002).doc
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OSHA 29 CFR 1919.1000 requires that employee exposure to airbome toxicants be
monitored upon initial exposure and repcatcd when there is a significant process change.
This should be done by a certified industrial hygienist (CIH) with experience in the
evaluation and control of toxic dusts. Worker exposure must be less than 50% of the
OSHA 8-hour time weighted average (TWA). This is known as the action limit and is 25
micrograms/cubic meter in air.
Cement is typically made of primarily two ingredients: quartz (17-25%) and lime (60-
65%) in addition to other materials at less than about 3Yo each. The lime (calcium
hydroxide) dissolves in water to produce an alkaline solution with a pH of about 12.5.
Calcium hydroxide solutions can cause chemical bums to the skin and eyes. Personal
protection in the form of skin and eye protection as well as respiratory protection is
needed. For reference OSHA's standard for skin and eye protection is 29 CFR 1910.132.
In summary worker protection includes eye, skin and respiratory protection with
engineering controls being the primary means of accomplishing this.
Sirrcerely,
Jef['F, PothasE CnH
C€rtifr d Indusfrial Hygienim
(CEOof"BFA nnc")
C:\Users\jplano\AppData\LocalMicrosoft\Windows\INetCache\Content.Outlook\3PUEB3GK\1601 Garfield
County - Fabric Enclosure for Concrete Processing (002).doc
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