permissible exposure limits (pels) time weighted average (twa) american conference of governmental...
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New Proposed Silica Standard
Jon NixonSafety Specialist
CenterPoint Energy
Acronyms
Permissible Exposure Limits (PELs) Time Weighted Average (TWA) American Conference of
Governmental Industrial Hygienist (ACGIH)
National Institute for Occupational Safety and Health (NIOSH)
Silica
Silicon + Oxygen = SiO2
One of the most abundant compounds Two Forms
› Crystalline› Non-Crystalline
Found in nature as quartz
Silica
Non-Crystalline (amorphous) Crystalline
› Quartz› Crystobalite› Tridymite
Uses
Glass Filler for:
› Paints› Plastics› Rubber
Fiber Optics
Operations
Glass Workers Construction Work Utility Work Sandblasting Quartz Mining Masonry Work Demolition
Portland Cement
How many will be affected?
~ 2.2 Million workers in the U.S.› 1,850,000 in Construction› 320,000 in General Industry/Maritime
Health Effects
Essentially non toxic› LD50 of 5,000 mg/kg
Silica Dust can lead to:› Silicosis› Bronchitis› Cancer
Silicosis Disabling and sometime fatal lung
disease with no current cure Due to inhalation of silica dust Characterized by:
› Shortness of breath› Cough› Fever› Cyanosis (bluish skin)› Scaring in the lungs
https://www.youtube.com/watch?v=6FezczBUnI0
Typical Healthy
LungsSilica Exposure
Typical Healthy
LungsSilica Exposure
Silica Exposure
Acute vs Accelerated vs Chronic Concentration Duration Particle Size
Acute Silicosis
Develops after 1 to 3 years of exposure at a very high concentration
Symptoms may show as early as 7 months
Cough, weight loss, and extreme fatigue
Liquid in the alveoli Fatal with in 2 years
Accelerated Silicosis
Shorter exposure than Chronic, 5-15 years
Higher concentration Progresses after employee is removed
from the exposure source
Chronic Silicosis
Long term exposure, 20-45 years, to develop
Dust with 10% or greater silica Little to no symptoms for the first 20
years Shortness of Breath, cough, fever Bluish lips/ear lobes Chest Pain
History OSHA current standards adopted in
1971 OSHA had to promulgate PELs
› 425 were created Silica’s PEL was derived from
› Walsh-Healy Public Contacts Act › Contract Work Hours & Safety Standard’s
Act› ACGIH
History
In 1974 NIOSH recommended that the occupational exposure be controlled so that no worked is exposed to:› TWA greater than 50 µg/m3
10 hour workday 40 hour work week
History
OSHA’s National Emphasis Program› NEP Launched 1/24/2008› Included:
Compliance Enforcement Consolation Training and Outreach through the OSHA Web-
site Standard Development
Regulations
General Industry› 1910.94
(Ventilation)› 1910.1000 Table
Z-3 (The Z Table)
Regulations
Shipyard Industry› 1915.34
(Mechanical paint removal)
› 1915.1000 (The Z Table)
Regulations
Construction Industry1926.55 (Appendix A Dusts)
1926.57 (Ventilation)
Regulations
Current exposure limits› Adopted for decades ago
U.S. National Toxicology Program, International Agency for Research on Cancer, and NIOSH have identified respireable crystalline silica as a human carcinogen
› PELs are difficult to understand› Based on older sampling methods› Shipyard workers PEL is 2x general
industry
OSHA’S Proposed Rule
Two proposed standards:› One for General Industry/Maritime› One for Construction
Why are they considering a change?
OSHA estimates current lung cancer deaths from exposure to silica over a 45 year working life averages: › Between 13 – 60 General Industry deaths
per 1,000 workers average exposure is estimated to be ~
100µg/m³› Between 37 – 635 Construction & Shipyard
deaths per 1,000 workers Average exposure is estimated to be ~
between 250 – 500 µg/m³
Why are they considering a change?
Supreme Court: “significant risks are present and can be eliminated or lessened by a change in practices” before promulgating any health or safety standard.
After standard implemented:› Estimate between 6 – 26 deaths per 1,000
workers.
Why are they considering a change?
Current Permissible Exposures Limits (PELs) are formulas that many find hard to understand:› PEL (respirable fraction) = 10 ÷ [% quartz
+ (% cristobalite × 2) + (% tridymite × 2) + 2]
› PEL (total dust) = 30 ÷ [% quartz + (% cristobalite × 2) + (% tridymite × 2) + 2]
Why are they considering a change?
Constriction/shipyard PELs are obsolete particle count limits
Construction/Shipyard formulas are about 250 µg/m3
General Industry formula is equal to about 100 µg/m3
What are other countries doing?
Canada› Alberta – 25 µg/m3
› Nova Scotia – 25 µg/m3
› Saskatchewan – 50 µg/m3
Italy 25 - µg/m3
Ireland – 50 µg/m3
Netherlands – 75 µg/m3
OSHA’s Proposed Rule Establishes new PEL of 50 μg/m3 = 0.05
mg/m³ Includes provisions for:
Measuring worker exposures to silica; Limiting access to areas where workers
could be exposed above the PEL; Use of dust controls; Use of respirators when necessary; Medical exams for highly exposed workers; Worker training; Recordkeeping.
Exposure Assessment
Conduct an initial exposure assessment› This will determine if:
EE’s are exposed to Silica levels at or above the action level
Whether or not engineering/administrative practices are required to reach the PEL
Determine if periodic or additional monitoring will be needed
NIOSH Sampling Method
NIOSH Method 7500 http://www.cdc.gov/niosh/docs/2003-
154/pdfs/7500.pdf
NIOSH Sampling Method
NIOSH Sampling Method
Methods of Controls
Methods of Control
Use engineering controls and work practices to maintain exposure levels at/or below the PEL
If the employer can show that engineering controls are not feasible:› Attempt to reduce the exposure to the
lowest achievable level› Supplement with PPE
Methods of Control
If blasting, use alternative media Ventilation Wet Method PPE
What is CNP doing?
What are we doing?› Monitoring the “situation”› Gathering information
Historical Sampling Data Field Interviews
› Preparing for NEAs
Where can I get more info?
OSHA› https://
www.osha.gov/dsg/topics/silicacrystalline/additional_info_silica.html
NIOSH› http://
www.cdc.gov/niosh/npg/npgd0552.html
Questions?
Thank you for your attention and time.
Jon Nixon CenterPoint Energy 713.967.7073