Silica


Problem:

Workers that jackhammer concrete surfaces may face hazards from silica.

Risk Description:

Inhaling crystalline silica can lead to serious, sometimes fatal illnesses including silicosis, lung cancer, tuberculosis, and chronic obstructive pulmonary disease (COPD).  When workers breathe in dust containing silica the lung tissue reacts by developing fibrotic nodules and scarring around the trapped silica particles. This fibrotic condition of the lung is called silicosis.  If the nodules become too large, breathing becomes difficult and death may result.  Silicosis may develop after very short periods of high exposure, but more commonly it develops after many years of lower levels of exposure. There is no cure for silicosis.

Initially, workers with silicosis may have no symptoms. As silicosis progresses, they may experience difficulty breathing and other chest symptoms such as a cough. There are  three types of silicosis:

  • Chronic silicosis, which usually occurs after 10 or more years of exposure to crystalline silica at relatively low concentrations;
  • Accelerated silicosis, which results from exposure to high concentrations of crystalline silica and develops 5 to 10 years after the initial exposure; and
  • Acute silicosis, which occurs where exposure concentrations are the highest and can cause symptoms to develop within a few weeks to 4 or 5 years after the initial exposure.

In 1996, the World Health Organization – International Agency on Cancer Research (IARC) changed its classification of crystalline silica from a probable human carcinogen to a known human carcinogen.  In 2009, IARC reaffirmed its position noting “[an] increased risk of lung cancer was observed across various industries and processes.”

Exposure to silica has also been linked to renal disease and rheumatoid arthritis.


Level of Risk:

There are numerous studies detailing the silica exposure-disease relationship.  NIOSH estimates that at least 1.7 million workers may be exposed to respirable crystalline silica and that many are exposed at levels exceeding current standards (http://www.cdc.gov/niosh/topics/silica/).  In addition, a study of death certificates of white males under age 65 found a 3 fold increase in the risk of death from silicosis among construction workers based on proportionate mortality ratios (“Assessment of mortality in the construction industry in the United States, 1984–1986,” Robinson, et, al, 1995).  A 2003 study (“Estimating the Total Number of Newly-Recognized Silicosis Cases in the U.S.,” Rosenman, et, al, 2003) found further evidence that cases of silicosis are significantly underreported.  Using information from death certificates combined with data from a state-based active surveillance system, the researchers estimated that there were “3,600 to 7,300 [silicosis] cases per year in the United States from 1987 to 1996.”

The following documents from NIOSH provide extensive detail on the exposure-disease relationship.

•    Health Effects of Occupational Exposure to Respirable Crystalline Silica (NIOSH Pub# 2002-129)
•    Preventing Silicosis and Deaths in Construction Workers (NIOSH Pub# 96-112)
•    Occupational Health Guideline for Crystalline Silica, September 1978


 

REPORTED AVERAGE EXPOSURES TO RESPIRABLE SILICA AND RESPIRABLE DUST IN CONCRETE-RELATED WORK BY TASK, TOOL, AND ENGINEERING CONTROLS

(Tools if reported) Engineering Controls NR= Not Reported Task Mean(SD) Respirable Silica Task GM (GSD) Mg/M Respirable Silica Task GM (SD) Mg/M Respirable Particulate Source
CONCRETE SURFACE GRINDING          
Surface Grinding Local exhaust Ventilation (High)   1.7 (1.34)   Croteau et.al. 2002
Surface Grinding Local exhaust Ventilation (Low)   2.4 (1.7)   Croteau et.al. 2002

Surface Grinding
(Outside)

Local Exhaust ventilation   2.44 (1.6)   Flanagan et.al. 2003
Surface Grinding
(Inside)
Box Fan     1.42 (2.49) Flanagan et.al. 2003
Surface Grinding (Commercial Building) NR     2.71 (2.39) Croteau et al. 2004
Surface Grinding (Commercial Building) Local exhaust ventilation (3 shroud configurations)     4.5 Croteau et al. 2004
Concrete grinding (surface finishing). Hand-held Local exhaust ventilation + high wind velocity 0.26 (0.33) Min-Max = 0.04-0.75   0.14 Akbar-Kanadaseh et.al. 2002
Concrete grinding (surface finishing). Hand-held Local exhaust ventilation + low wind velocity 0.43 (0.28) Min-Max = 0.03-1.00     Akbar-Kanadaseh et.al. 2002
Concrete grinding (surface finishing). Hand-held high wind velocity only 0.61 (0.50) Min-Max = 0.02-1.80     Akbar-Kanadaseh et.al. 2002
Concrete grinding (surface finishing). Hand-held low wind velocity only 1.93 (1.64) Min-Max = 0.17-7.10     Akbar-Kanadaseh et.al. 2002
Concrete grinding. Hand-held grinder. Wet 0.02     Linch 2002
Concrete grinding. Hand-held grinder. Local exhaust ventilation ND-0.13     Linch 2002
Concrete grinding. Hand-held grinder. None 0.66     Linch 2002

Surface Grinding
(Inside)

None   6.27 (2.44)   Flanagan et.al. 2003

Surface Grinding
(Outside)

None   4.87 (2.41)   Flanagan et.al. 2003
Concrete Surface Grinding None   29.16(1.24)   Croteau et.al. 2002
Concrete Surface Grinding None 0.13-0.66      
Concrete Surface Grinding          


Assessment Info:

Work Safely with Silica” at www.silica-safe.org provides information needed to assess the risk, determine if a material contains silica, and an on-line tool to create a job hazard analysis and plan for controlling exposures.

To determine if your worksite has high exposures to silica during these operations, you should: see if the materials you are using contain silica (materials or products containing more than 0.1% silica must be labeled) and measure exposure.


Regulations & Standards:

OSHA has a Permissible Exposure Limit (PEL) for exposure to crystalline silica under 29 CFR 1926.55(a) of 0.1 mg/m3 based on an 8-hour time weighted average.  OSHA also requires hazard communications training for workers exposed to crystalline silica, as well as a respiratory protection program until engineering controls are implemented. 

In September 2008, CalOSHA issued a standard “Control of Employee Exposures from Dust-Generating Operations Conducted on Concrete or Masonry Materials.”

In December, 2004, New Jersey signed a law prohibiting the dry cutting and dry grinding of masonry.

NIOSH recommends an exposure limit lower than the OSHA PEL.  The NIOSH Recommended Exposure Limit (REL), published in 1974, is 0.05 mg/m3 based on a time-weighted average for up to 10 hours.

The American Conference of Industrial Hygienists (ACGIH) recommends a Threshold Limit Value of 0.025 mg/m3 based on an 8-hour time-weighted average.

Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.


Other Considerations:

One study, “A case-control study of airways obstruction among construction workers”, examined occupational exposures to vapors, gases, dusts and fumes (VGDF) among older construction workers between 1997 and 2013, comparing 834 workers with COPD and 1,243 controls.  Approximately 18% (95% CI=2-24%) of COPD in this population can be attributed to workplace exposures associated with construction tasks.  After adjusting for smoking habits in this population, the study also revealed among construction workers who never smoked, 32% (95% CI=6-42%) of COPD was attributable to the workplace.