4.15 Sand Blasting

4.15.1 Emissions

Introduction

Abrasive blasting (of which sandblasting is a part) is the use of abrasive materials to clean or prepare a surface, such as metal or masonry. Sand is the most commonly used abrasive material. Other abrasives include coal and smelter slags, glass beads, aluminum oxide, steel shot, walnut shells, garnet, etc. Industries that use abrasive blasting include ship building and repair, aircraft manufacturing, fabricated metal manufacturing, oil and gas extraction industries, aluminum and other nonferrous production and processing industries, etc.

There are three types of propelling methods used for abrasive blasting:

  1. Dry System where compressed air is used to propel the abrasive using either a suction or pressure type process.
  2. A wet system where air or water pressure are used to propel an abrasive slurry to the target surface.
  3. Centrifugal Wheel System where centrifugal and inertial forces are used to propel abrasive materials.

In many applications, the abrasive materials can be reused. However, once the abrasive’s particle size gets smaller, its stripping efficiency drops and has to be replaced. On the other hand, sand is commonly used for abrasive operations where recycling is not feasible, such as unconfined sand blasting operations.

Methodology

The District’s Data Bank system contains information on companies with abrasive blasting operations in the Bay Area. These sources are considered point sources. Sand is the most commonly used abrasive material, however there are other abrasive materials used in the Bay Area, such as steel shot, glass beads and aluminum oxide. For emission calculation purposes, it is assumed sand is used in both point (Category 42) and area sources (Category 1909). The other abrasive materials’ usages were in the point sources (Category 42).

Throughput Calculations

The 2011 sand throughput was estimated from the U. S. Geological Survey’s (USGS) Mineral Commodity Survey. According to this survey, abrasive sand consumed approximately 3.7% of the industrial sand production in 2010. (At the time, this was the latest data available.) California received approximately 4.4% of the total sand produced. The BAAQMD’s percentage of California’s total abrasive sand throughput was approximately 12.6%. This was estimated by using the ratio of the number of employees associated with abrasive blasting (by NAICS) in the District versus California. The following industries were used for this calculation:

  • Ship building and repair (NAICS 3366)
  • Aircraft manufacturing industry (NAICS 336411)
  • Steel product manufacturing industry (NAICS 3312)
  • Aluminum production and processing industry (NAICS 3313)
  • Nonferrous production and processing industry (NAICS 3314)
  • Fabricated metal product manufacturing industry (NAICS 332)
  • Oil and gas extraction industry (NAICS 211)

Using these figures, the 2011 estimated total sand throughput in the Bay Area is as follows:

2010 Sand usage in the United States (from the USGS’s Salient U.S. Silica Statistics:

\[\begin{align} 28,749,347&\ \text{ton/yr} \\ \end{align}\]

2010 Bay Area sand usage for abrasive purposes:

\[\begin{align} 28,749,347&\ \text{ton/yr} \\ \times\ 0.037&\ \text{(for abrasive purposes)} \\ \times\ 0.044&\ \text{(to Calif.)} \\ \times\ 0.126&\ \text{(BAAQMD portion)} \\ \hline = 5,937&\ \text{ton/yr} \end{align}\]

Subtracting out the 2010 point source (permitted) sand throughput of 2,570 tons/year to get the 2010 area source throughput yields:

\[\begin{align} 5,937 & & \text{(total)} \\ – 2,570 & & \text{#42 (point)} \\ \hline = 3,367 &\ \text{ton/yr} & \text{#1909 (area)} \end{align}\]

The 2011 area source throughout of 3,413 tons/year was estimated by multiplying the 2010 area source throughput by the Association of Bay Area Government’s (ABAG’s) Manufacturing and Wholesale Employment growth factor.

Emission Calculation

U.S. EPA (1998) recommended particulate emission factors for sand blasting were used for emission calculations. They are as follows:

  • PM: 54 lbs/ton
  • PM10: 26 lbs/ton

The 2011 Area Source Sand Blasting emissions (Category 1909) for total particulates (PM) and PM10 in the BAAQMD are as follows:

\[ \begin{eqnarray} \text{PM} &=& 3,413\ \text{ton/yr} \times 54\ \text{lb/ton} \div 2000\ \text{lb/ton} \\ &=& 92.15\ \text{ton/yr (or 0.25 ton/day)} \end{eqnarray} \]

\[ \begin{eqnarray} \text{PM}_{10} &=& 3,413\ \text{ton/yr} \times 26\ \text{lb/ton} \div 2000\ \text{lb/ton} \\ &=& 44.37\ \text{ton/yr (or 0.12 ton/day)} \end{eqnarray} \]

The 2011 point source (Category 42) total particulate emission was 0.10 ton/day.

Monthly Variation

The monthly variation of emission was estimated to be approximately three times the amount during the period of April through October as opposed to the rest of the year.

County Distribution

For point sources (Category 42), the data bank system contains information on the county location of each processing plant; hence, emissions are distributed to the counties accordingly. Emissions from area sources (Category 1909) were distributed to counties by the total employment estimates from those industries listed above by NAICS.

Table 4.30: County fractions.
category ALA CC MAR NAP SF SM SNC SOL SON
#42 Sand Blasting 35.0% 6.0% 1.0% 1.0% 2.0% 8.0% 40.0% 4.0% 3.0%
#1909 Sand Blasting (Area) 35.0% 6.0% 1.0% 2.0% 2.0% 7.0% 38.0% 6.0% 3.0%