Silica Exposure Control Programs in the Drilling Industry
We are all gaining familiarity with “Table 1. SPECIFIED EXPOSURE CONTROL METHODS WHEN WORKING WITH MATERIALS CONTAINING CRYSTALLINE SILICA” of OSHA’s Crystalline Silica Rule for Construction – a title that kind of rolls right off the tongue. Table 1 was OSHA’s attempt to guide contractors in reducing silica exposure below the new permissible exposure limit (PEL) of 50 ug/m3. For most of the construction industry, it largely works and boils down to two things – use water or use a vacuum. Common tasks such as cutting, chipping, drilling and grinding concrete are listed in Table 1 along with the precautions the contractor must do to stay below the PEL. Do these tasks with these precautions and you’re all set. But what happens when your task is not listed? This is the place that the drilling industry finds itself.
The tie-back and micropile industry drills rock on a regular basis. According to Encyclopedia Britannica, “The mass of Earth’s crust is 59 percent silica, the main constituent of more than 95 percent of the known rocks.” OSHA requires that exposure to safety or health hazards be eliminated through administrative or engineering controls if possible. Our industry most commonly drills rock with down the hole hammers. These hammers are single pistons at the bottom of the drill rods that actuates a bit up and down through the power of high pressure, high volume air compressors. The primary engineering control is to drill with water. The volume and pressure of the water must be sufficient to reduce silica exposure below the PEL. So how do we know that we are protecting our workers during drilling? We test.
The OSHA rule for silica exposure has two options for assessing employee exposure when not following Table 1 – the Performance Option and the Scheduled Monitoring Option. The Performance Option requires assessing employee exposure based on any combination of testing and objective (read industry) data. Unfortunately, we don’t have industry data, but we’re working on it. More from ADSC on this in the future. At Subsurface Construction are focusing on the Scheduled Monitoring Option for drilling. Scheduled Monitoring means testing for respirable silica on individual employees while drilling with engineering controls in place. Depending on the results, OSHA guides the employer as to what additional testing is required. Unfortunately, monitoring is not a one-time event as the rock formations and drilling conditions can vary site to site. To date, we have not been over the PEL when drilling rock with water, but we will continue to wear respirators as we gather more data.