Silica exposure and respiratory health risks in construction workers

Silica Exposure in Construction Workers

Construction workers that breathe dusting containing respirable crystalline silica may lead to a deadly lung disease known as silicosis. Unfortunately, treatment does not exist for silicosis. However, it is preventable through controlling a worker's exposure to crystalline silica. Other disease linked to silica exposure are kidney disease, lung cancer, reduced lung function as well as other disorders. Construction materials like mortar, concrete, block, and brick contain crystalline silica.

The recommend limit of exposure for crystalline silica is 50 micrograms per cubic meter for up to 10 hours each workday in a maximum 40-hour workweek. The fraction of aerosol that is tiny enough to each deeper gas-exchange areas of the lung is categorized as respirable dust. High construction tasks for example, produce respirable dusts that often contain crystalline silica. Such tasks include concrete saw cutting and concrete core drilling. Even in interior construction, efforts, such activities as drywall finishing, which involve dry and wet sanding and applying can increase rate of exposure to crystalline silica.

In order to perform the drilling as seen in highway construction, construction workers use dowel-drilling machines to drill horizontal holes within concrete pavement. This paper will focus on an in depth literature review of silica exposure while performing these activities. It will look at past data and studies in order to develop controls and evaluate exposures to silica to identify activities and work habits that either reduce or increase silica exposure for construction workers. The methodology section will contain a sampling as well as results that will test the hypothesis generated in the essay.

Silica exposure is more common than believed and can happen in highway construction as much as home renovation. Certain work patterns and personal work habits may prevent serious silica exposure. The opposite can also be said as some may increase exposure.

II. Introduction

Dust can be hazardous to construction workers. This is because much of the dust during construction may contain crystalline silica. This respirable dust can reach the lungs and have the potential to cause serious disease to those who are exposed to it. Such serious diseases are lung disease, lung cancer, silicosis, as well as other system illnesses. Therefore, recommendations for respiratory protection and work practices must be in place in order to prevent such incidents from happening.

The most common type of crystalline silica is Quartz. Quart accounts for nearly 12% by volume of earth's crust and is the second most common type of surface material. Quartz exists within numerous materials such as mortar, brick, concrete, dimensional stone, slate, tile, stone aggregate, and sand utilized for blasting. Other kinds of construction materials that also contain crystalline silica are roofing granules, asphalt filler, soils, plastic composites, and to a lesser level, paint, plaster, putty, caulking, and some wallboard joint compounds. Other than quarts, cristobalite also exists several high temperature exposed places like some ceramic tiles, brick lining of vessels and boilers and even volcanic ash.

Such common occurrence of quartz and to a lesser extent, cristobalite, demands that construction workers take precautions when performing certain tasks. For example, highway construction involves concrete saw cutting and concrete core drilling. Interior construction may involve drywall finishing: applying, dry sanding, and wet sanding. These activities all require construction workers to take safety precautions in order to minimize silica exposure.

The crystalline silica allowable exposure limit for the construction industry lies at 29 CFR 1926.55(a) and is expressed in terms of millions of particles per cubic foot or mppcf (OSHA.GOV, 2009, p. 3). In terms of increase or decreasing likelihood of crystalline silica exposure, it all depends on the concentration of silica within materials located in construction sites. In addition, factors experienced in the work environment. These could include semi-enclosed, enclosed, open spaces, and/or multiple operations creating silica dust. Environmental conditions can also play a part such as wind speed and direction.

Organizations like OSHA encourage employers conduct intermittent exposure monitoring to confirm work and engineering practice controls remain effective as well as that suitable respiratory protection is being utilized when required. Controls continually evolve such as equipment modification. Anyone working in construction should take precautions working in any environment, whether it be outdoor or indoor. This paper will highlight levels of exposure in the multiple settings discussed: concrete saw cutting; concrete core drilling and drywall finishing: applying, dry sanding, and wet sanding using literature and past studies.

Such information will help reveal the need to use respiratory protection while performing the tasks within the list. It will also show how to develop controls and evaluate more effectively exposures to crystalline silica. The problem is over exposure to silica during construction activities and the solution lies in creating awareness of how much exposure as well as forming effective controls to reduce crystalline silica exposure.

If construction workers ae aware of which activities produce high levels of crystalline silica exposure and the kind of precautions needed to prevent breathing such hazardous material, overall exposure rates can diminish. Organizations like OSHA already have in place safety precautions to reduce crystalline silica exposure. This paper will also conduct a sampling and review past data in order to compare data from current studies.

The literature review will add additional information on past information. It will provide information on techniques that were successful at reducing exposure to crystalline silica as well as protection equipment that was useful in preventing increased exposure. Each section will cover one activity and or development of identification and implementation.

a. Problem

Over exposure to silica during construction activities is an ongoing problem experienced by construction workers. Numerous construction activities may put construction workers at risk of inhaling silica-containing dusts, and there is significant body of literature detailing exposure levels by means of a task-based strategy. In a 2012 study, researchers used statistical modeling to examine a data set that contained 1466 task-based, individual RCS or respirable crystalline silica measurements collected from 46 sources to approximate exposure levels for the duration of construction tasks as well as the effects of factors of exposure.

Suave et al. used the Monte -- Carlo simulation to recreate personal exposures from summary limits. The statistical modeling involved multimodal inference "with Tobit models containing combinations of the following exposure variables: sampling year, sampling duration, construction sector, project type, workspace, ventilation, and controls. The model containing all the variables explained 60% of the variability and was identified as the best approximating model" (Sauve et al., 2012, p. 432). From the twenty-seven tasks checked in the data set, masonry chipping, abrasive blasting, scabbling concrete, tunnel boring, and tuck pointing had estimated geometric averages above 0.1mg m?3 established on the exposure scenario developed.

When examining activities that involve anything that disperses particles readily like tunneling and sawing, crystalline silica was found in higher levels than when no such activities were performed. This is important in order to identify properly which activities are more prone to crystalline silica exposure than others are. Construction workers perform many activities during work hours. Examining their work habits and safety standards established within the workplace may help reduce the problem of overexposure in construction activities. Quartz is very common among surface materials especially in construction. Reduction of exposure must be met in the majority of construction activities, even indoor ones like dry walling.

b. Background

Silica, a naturally occurring mineral in soil and rock, is the second most abundant mineral on the earth's surface. When a person inhales, silica dust can cause cancer, silicosis, and increases the risk of developing Tuberculosis or TB infection. Crystalline silica or airborne silica is present in many industries like mining, foundry work, concrete manufacturing, glass, stone crushing, pottery, painting, and most importantly, construction.

The stone crushing industry has high rates of silica exposure with many cases reported in developing countries. This is due to most mills operating without dust controls. An estimated 12,000 stone crusher mills exist in India alone and provide direct employment for over 500,000 workers, many of whom are underprivileged women and children. Statistics from the Indian Government estimate ten million people are exposed to crystalline silica dust while on the job. Studies highlight the common occurrence of lung disease, TB infection, and silicosis among those exposed to silica dust.

Work-related exposure to silica dust within the mining industry is an international concern. Most developing countries' labor force is comprised primarily of migrant workers. Attrition rates among that population are high. "Over one million mineworkers in China and 500,000 in South Africa have been diagnosed with silicosis. In southern Africa migrant workers in mineral mines experience higher rates of HIV and an associated TB incidence that is reportedly ten times that of the general population" (Okinternational.org, 2015). India's mining industry offers employment to more than 1.1 million people. Thousands more are employed in unofficial, small mines. Although the number of people exposed to silica dust remain high in these areas, diagnosis for silica-related diseases like silicosis are low. The Indian government must promote awareness of such illnesses to prevent complications in those exposed to silica dust. This can also be applied to construction workers in general.

i. Concrete Saw Cutting

Concrete saw cutting is one of the activities that exposes construction workers to crystalline silica. When construction workers cut concrete dry versus wet, exposure levels of crystalline silica are high. Therefore, many believe water spray offers sufficient control to limit worker exposures to levels below the silica PEL. Research shows water spray-controlled versus dry or uncontrolled crystalline silica provide a noticeable and significant reduction in terms of dust production. "A NIOSH study found a mean exposure of 0.09 mg/m3 for four wall saw/core drilling exposures. These limited data suggest that water application often, although not always, maintains the silica content below the PEL" (Flanagan, Loewenherz & Kuhn, 2001, p. 1097).

Wet saw cutting is a major reducer of crystalline silica in concrete cutting. This is because it prevents particles from dispersing into the air and filling the lungs of workers utilizing such tools. "Water appears to be effective for reducing concrete core drilling emissions. When the core bit is sunk into the concrete, dust particle velocity is slowed and mixed with water before exiting the borehole, emitting slurry with little velocity to produce an airborne aerosol" (Flanagan, Loewenherz & Kuhn, 2001, p. 1100). When dry cutting, particles are more readily dispersed into the air, resulting in increased exposure. Although protection equipment like face masks may lessen exposure, it may not do so as well as using water to perform the cutting.

Construction workers in general in modern countries, utilize water frequently when using saws. This is because of the aforementioned reduction in particle dispersal in the air, but also because it makes cutting concrete easier. It is an excellent way to improve the safety of construction workers as well as decrease likelihood of silica exposure.

ii. Concrete Core Drilling

Concrete core drilling similar to concrete saw cutting has potentially devastating effects to one's health if drilling dry. A 2002 study assessed the efficacy of "commercially available local exhaust ventilation (LEV) systems for controlling respirable dust and crystalline silica exposures during concrete cutting and grinding activities" (Croteau, Guffey, Flanagan & Seixas, 2002, p. 458). Union-sponsored apprentices performed work activities that included tuck-point grinding, brick cutting, surface grinding, paver block, and concrete block cutting with hand-held saw. Three ventilation rates: 0, 30, and 75 cfm, were tested for every tool. Ventilation treatments were replicated three times all in random order during nine 15-min work sessions per participant. The results showed major reduction in silica or respirable dust exposure, with the exception of the hand-held saw. In fact, average exposure levels for 75 cfm treatments had less rates of exposure than the 30 cfm treatments. Although exposure decrease was noteworthy (70-90% low ventilation rate, 80-95% reduction high ventilation rate), individual respirable dust exposures remained very high.

This study is important to note because while wet drilling and sawing can be useful in reducing individual silica exposure, ventilation efforts may not be as effective. Concrete core drilling is often done dry as seen in various construction projects throughout the world. This can be very hazardous because of the amount of silica drilling disperses to an individual drilling. Construction workers may opt for dry drilling because it is less expensive and requires less clean up than wet drilling. However, latest research shows improvements in wet drilling with Micro-nano-based drilling fluid. This is because researchers claim micro-Nano composite materials have excellent potential for creating intelligent drilling fluid. "The results showed that the composite, as a micro-nano drilling fluid additive, possessed excellent properties such as thermal stability, rheology, fluid loss and lubricity. Especially, it could plug the formation effectively and improve the pressure bearing capability of formation significantly" (Mao et al., 2015, p. 90).

iii. Drywall Finishing

Construction jobs often include drywall finishing. Sanding and finishing drywall joint compound can be a dusty construction action. Simmons, Jones & Boelter studied potential factors that may influence exposure to respirable as well as total dust for bystanders and sanders within the space of drywall joint compound finishing. They observed seventeen test events in a room-scale isolation chamber. The researchers found air change rate to negatively correlate with dust "Ctwa both in the sander's personal breathing zone and surrounding area. We could not conclude that sanding tool type systematically influences dust Ctwa, but the use of 80-grit abrasive was associated with the highest dust Ctwa" (Simmons, Jones & Boelter, 2009, p. 324). They also found respirable dusts uniformly dispersed 1-8.2 m away from sanding activities in a fixed location. Both total and respirable dust Ctwa found in the sander's personal inhalation zone are greater than in the nearby area. The respirable portion of the whole dust mass Ctwa was more in the adjacent area than in what was in the sander's personal inhalation zone. The concentrations of respirable dust measured increased over the period of sanding, showing a temporal trend similar to what was predicted. An interesting thing to note form the article was dust concentrations resumed to pre-activity or background levels 2 to 4 hours after termination of the sanding activity.

This means while there is an increase in dust when sanding drywall, the overall amount of dust after will dissipate in a relatively short period. However, the information also suggest, the dust can affect not just the sander but also anyone nearby. Safety measures must take into consideration the amount of dust dispersed in and around the area.

1. Applying

Application of drywall can be difficult in terms of reducing exposure to silica and other dust particles. There is a lot of sanding involved that disperses particles into the air. Even after the sanding is completed, the particles can stay in the air for up to four hours. This means any construction workers working on or near the area that is finishing drywall, will be exposed dust particles, including silica for up to four hours.

Any exposure to silica can be hazardous, but over time, it can prove deadly. There are two types of application when it comes to drywall finishing. Dry sanding and wet sanding. Dry sanding causes the most particle dispersal and increases chances of greater crystalline silica exposure. Wet sanding decreases the chances since liquid is being used to sand. Any construction activity using liquid will decrease the amount of particles dispersed into the air.

It is highly unlikely construction workers will wear facemasks for example, to protect themselves from the crystalline silica for four hours. Most likely, they will take them off after application and continue working. Therefore, wet applications or wet sanding may be highly valuable in decreasing rates of exposure in construction workers aiming to reduce crystalline silica exposure. In the next sections, dry sanding and wet sanding will be discussed in order to understand the pros and cons of using either technique or why some construction workers will opt for one over the other.

2. Dry Sanding

Dry Sanding generates a lot of dust. This is because of the constant application of friction to the surface of the drywall. Since the drywall often contains a lot of crystalline silica. It disperses from the dry wall as the construction worker dry sands. The particles released from the sanding action last for several hours. Research has shown that exposure to crystalline and other potentially hazardous dust particles are higher from dry sanding than wet sanding. However, construction workers may use dry sanding because it is faster and involves less effort.

3. Wet Sanding

Wet sanding drywall is common among construction workers and is used to smooth the surface of any drywall compound. Although the term is called sanding, it is not actually sanding at all. Instead, a rag or sponge is used to soften the drywall compound. This technique reduces chances for crystalline silica exposure greatly. However, it is not as fast as dry sanding and does not actually sand anything, but rather smooths things. It has it use in construction, nevertheless it does not substitute what dry sanding does.

c. Scope and Objective

The scope of this paper will focus on past efforts performed to reduce silica exposure among construction workers, the effects silica exposure has on health, and the development of controls that may reduce silica exposure. Through conducting a sampling and researching past efforts to reduce silica exposure, an increased understanding of what techniques and approaches work will be expected.

1. Evaluate exposures to silica

Several techniques have been discussed that increase exposure to crystalline silica. Concrete drilling and sawing increase exposure to crystalline silica when it done dry. The same can be said of dry sanding drywall. There are other ways construction workers may be exposed to silica. Workers get increased exposure of crystalline silica during hydraulic fracturing. Hydraulic fracturing involves high-pressure injection of great volumes of sand and water, and smaller amounts of well treatment chemicals, into oil or gas wells to break shale or other rock growths. This allows effective recovery of hydrocarbons off a petroleum-bearing reservoir. "Crystalline silica ("frac sand") is commonly used as a proppant to hold open cracks and fissures created by hydraulic pressure. Each stage of the process requires hundreds of thousands of pounds of quartz-containing sand; millions of pounds may be needed for all zones of a well" (Esswein, Breitenstein, Snawder, Kiefer & Sieber, 2013, p. 347). Mechanical management of frac sand generates respirable crystalline silica dust, thus creating a potential exposure threat for workers.

2. Develop controls

Certain controls must be put in place in order to reduce occurrence of silica exposure. Employers have a responsibility to safeguard their workers from crystalline silica dust exposure when working on construction projects. Research shows when common construction work jobs involve the sanding, chipping, drilling, grinding, sawing, cutting, blasting, and sweeping of concrete/concrete products and are performed without utilizing dust controls, construction workers are exposed to floating silica concentrations far above the industrial exposure limits. Long-term/heavy short-term contact with airborne silica dust may cause severe lung disease.

Due to the major risk posed by respirable crystalline silica, it is important that all workers involved in operations that could possibly generate silica dust take precise action to guarantee that, as much as conceivable, a hazard is not formed. The employer can develop some controls as shown below.

Guaranteeing that materials (e.g., equipment, tools, personal protective equipment) as well as other resources like worker training materials are obligatory to fully maintain and implement ta sound ECP or exposure control plan.

Offering a job-specific exposure control plan for every project, outlining and detailing the work practices and methods that will be adhered to on each site. Attentions will include

Accessibility and delivery of all the required equipment/tools

Nature and Scope of grinding work to be performed

Control methods used

Kind of respiratory protection necessary

Coordination plan

Directing a periodic evaluation of the efficacy of the ECP. This may include an evaluation of the available dust-control expertise to guarantee these are chosen and used when practical.

Initiating sample of worker contact with concrete dust when non-standard work practices are present for which the control approaches to be used have not been proven to be sufficiently protective.

Maintaining records of training, crew talks, fit-test results, and inspections of equipment, work methods/practices, and PPE.

Organizing the work with the main contractor as well as other employers to guarantee a safe work environment.

b. Past data

In the last decade, many articles have come out to show the dangers of silica exposure and offer solutions. In an article about silica exposure and solution, it discusses the primary way to decrease crystalline silica exposure. "Water, ventilation, or isolation can reduce the dust getting into the air. Respirators can protect the worker from breathing the dust. Water is often the best option for dust control" (University of Washington, 2015). It works greatest when a person directs water spray right at the point of grinding or cutting. A fine mist is usually more effective versus a water stream.

Another article highlights the data from studies. The results of exposure to silica dust during construction tasks like concrete finishing within construction settings are uncommon due to the frenzied nature of the activity as well as the presence of countless confounding influences. Researchers collected 49 personal respirable dust samples during concrete finishing during the time workers utilized hand-held grinders. Only 31% or 15 grinders were fitted out with local exhaust ventilation/LEV systems. The perplexing factors like wind velocity and direction, ambient temperature, and relative humidity were determined. To create a more specific sampling task, researchers activated air sampling only during real grinding.

The concentration of total respirable particulate ranged from 0.34 to 81 mg/m3, with a mean ± SD of 18.6 ± 20.4 mg/m3, and the concentration of crystalline silica in the samples ranged from 0.02 to 7.1 mg/m3, with a mean ± SD of 1.16 ± 1.36 mg/m3. LEV on the grinders reduced the silica dust level significantly (P < 0.01) compared to grinders without LEV (AKBAR-KHANZADEH, 2002, p. 341).

Another article explains the frequency of vast quantities of silica in materials used within the construction industry. When such materials are shaped or cut with power tools often times major respirable dust can be produced. The article examined and evaluated three dust control systems used with cut-off saws on site. They are wet dust suppression by means of mains water, local exhaust ventilation, and the same system via water from a transportable water tank.

The efficacy of water suppression on used cut-off saws has been exactly quantified in controlled research laboratory conditions by way of measurements with/without dust control. The average concentrations of airborne crystalline silica were minimized by an element of between 3 and 7, the exactness being partial by the comparatively high limit of exposure for silica. Everything in terms of controls systems largely lessened respirable dust levels at least 90%. Efficacy did not depend on blade type. However, "a diamond blade was more effective than a resin-bonded blade with the pressurized water system; cutting a slab with this type of blade could be completed before the water tank required repressurization." (Thorpe, 1999, p. 443).

Another article estimated probabilities of overexposure in the range of 64.5 and 100% for crystalline silica and the range of 8.2 and 89.2% for RSB dust. The data indicates that silica exposures are clearly unacceptable within the U.S. construction industry. Although engineering and administrative mediations are necessary to lessen overall air levels, the varied exposures among associates of each trade propose that controls should center, in part, upon the separate sites, equipment and activity involved. Effects of current controls as well as workplace features upon silica exposures were examined among laborers and operating engineers. Silica exposures were considerably decreased by "wet dust suppression (approximately 3-fold for laborers) and use of ventilated cabs (approximately 6-fold for operating engineers) and were significantly increased indoors (about 4-fold for laborers)" (RAPPAPORT, 2003, p. 111).

This literature review provided past data and studies on controls and measures including long-term effects of crystalline silica exposure. Gaps in research show the need for more studies in crystalline silica exposure with implemented controls as well as how long does crystalline silica exist within the air after performing a construction activity. Crystalline silica dust poses a significant threat and has posed it for over two hundred years affecting and killing millions of workers in trades including foundries, sandblasting, ceramics, jewelry manufacture, tunneling, brick making, and construction and mining.

More data is needed to grow awareness of the chronic and fatal conditions brought on by silica exposure like silicosis, tuberculosis (TB), heart disease, kidney disease, and chronic obstructive pulmonary disease. Without adequate research, cases of silica related illnesses will increase, especially in underdeveloped countries. Protocols should follow both inclusion of PPE as well as tools that use water and ventilation. Water clearly minimizes greatly the exposure to crystalline silica, so does ventilation, especially when combined together.