Construction Solutions work hazards, and options for making work safer
   
Hazard Analysis

  Work Activity: Pipes & Vessels  
  Task: Cut and drill holes in structures prior to pipe installation  
  Hazard: Silica  

  Problem:

Workers who cut and drill holes in structures prior to pipe installation may be exposed to silica.

  
  Risk Description:

Quartz (silica) is found naturally in almost all rock, sand and soil.  Although the primary component of joint compound is typically calcite (limestone), some forms do contain silica sand at levels that vary from non-detectible to as much as 25%.   Most are less than 3% silica.   When dust is generated from sanding joint compound or sweeping,  the dust will often contain silica.  The lung disease called "silicosis" is caused by breathing of dust containing silica. The dust causes "fibrosis" or scar tissue formation in the lungs. This reduces the lung's ability to extract oxygen from the air. Silicosis may develop after very short periods of high exposure, but more commonly it develops after many years of lower levels of exposure. Silicosis also increases susceptibility to other lung diseases and infections such as tuberculosis, and increases the likelihood of getting lung cancer.

When workers inhale crystalline 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 grow too large, breathing becomes difficult and death may result. A worker's lungs may react more severely to silica sand that has been freshly fractured, as happens when silica containing products are sawed, sanded, or treated in a way that produces airborne dust. This factor may contribute to the development of acute and accelerated forms of silicosis.

 A worker may develop any of three types of silicosis, depending on the airborne concentration of crystalline silica:

 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

 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

Complications

Initially, workers with silicosis may have no symptoms. As silicosis progresses, there may be difficulty in breathing and other chest symptoms such as cough. Individuals with silicosis are also at high risk of developing tuberculosis, which causes fever, weight loss, and night sweats. Tuberculosis or other infections are believed to result when the lung cells (macrophages) that fight these infections are overwhelmed with silica dust and are unable to kill the TB bacteria. About half of the mycobacterial infections are caused by Mycobacterium tuberculosis (TB), with the other half caused by M. kansasii and M. avium-intracellulare. Nocardia and Cryptococcus may also cause infections in silicosis.

Evidence indicates that crystalline silica is a potential occupational carcinogen.

 

 

 

 

 

 

 

 

 

 

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  Level of Risk:

Exposures are of such a magnitude and character that a significant number of workers risk developing serious long or short term health effects.

Silica and total dust exposures when grinding or polishing concrete can exceed recommended exposure limits.  In comparison,  silica exposures from sanding drywall joint compound containing silica sand are relatively low since most joint compounds contain little silica.  The easiest way to eliminate this hazard is to use joint compound where the MSDS does not list detectible levels of silica, quartz, or sand.   The relationship between silica exposure and development of silicosis is well known, and there is an OSHA standard for silica in general industry.  The following documents from NIOSH provide extensive detail on the exposure-disease relationship.

     Preventing Silicosis and Deaths in Construction Workers
     NIOSH Pub# 96-112

     Health Effects of Occupational Exposure to Respirable Crystalline Silica
      NIOSH Pub# 2002-129

NIOSH estimates that at least 1.7 million workers may be exposed to respirable silica and that many are exposed at levels exceeding current standards (NIOSH, 1991).  In a study of death certificates of white males under age 65, construction workers experienced a 3 fold increased risk of death from silicosis based on proportionate mortality ratios (Robinson, et, al, 1995). 

NIOSH published a criteria document for silica in 1974 which recommended that occupational exposure to respirable crystalline silica be controlled to reduce airborne exposures to a time-weighted average of 0.05 mg/m3.

Analysis of the silica database compiled by CPWR found the following:

  • Probabilities of exceeding the current ACGIH Threshold Limit Value (TLV) for silica ranged from 8% to 90% among the sampled construction trades.
  • The use of commercially available controls (e.g. water or ventilation) reduced exposures by 3 to 6 fold.

Limited published research finds use of vacuum dust collection for drywall resulted in a greater than 90% reduction in silica exposure.  Without controls, mean exposures were frequently above the NIOSH REL for silica.    A simple control like a pole sander (which moves the dust source further from the worker's breathing zone, or wet sponge sanding)  reduced silica exposure by about half, however, mean exposures for total dust may still be in excess of the NIOSH REL.  Vacuum dust collection is more effective.

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  Assessment Info:

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

A detailed guide to exposure assessment has been developed specifically for construction work:
 
     Guides for Managing Crystalline Silica Control Programs in Construction

OSHA has an e-tools site for silica that also walks you through this process:

     OSHA e-tool: Silica

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  Solutions:
Administrative control
PPE
Engineering control
  
  Regulations & Standards:

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.

See Regulations & Standards
 
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