Demolition contractors, operators of crushing plants and operators of several types of equipment used in the demolition and recycling process face the challenge of controlling dust.
When working at a jobsite or facility in a residential, commercial or mixed-use neighborhood, the importance of dust control escalates, as the last thing a contractor or sub-contractor wishes to deal with are nuisance complaints from neighbors.
Beyond maintaining good relations with neighbors are important safety and health reasons to suppress dust. Dust obscures the vision of processing equipment operators, mobile material handling vehicle operators and truck drivers, which can lead to accidents.
In regard to health, breathing in dust or particulates of any sort is unwelcome, but when it comes to the crushing of concrete, the dangers are escalated by the potential of long-term exposure to dust leading to silicosis.
A DREARY SCENARIO
On its website at www.osha.gov, the federal Occupational Safety and Health Administration (OSHA) paints a bleak picture of the potential effects of silicosis.
The agency says silicosis “is caused by exposure to respirable crystalline silica dust” and that “silica is a basic component of soil, sand, granite and most other types of rock and it is used as an abrasive blasting agent.”
Another way silica can be present in concrete is when silica fume is added to paving mixtures. Silica fume (also known as micro-silica) “is a byproduct of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys,” according to the Federal Highway Administration (FHWA).
Starting in the late 1970s, silica fume as a pavement additive was promoted as an alternative to discharging it into the atmosphere or landfilling it.
Subsequently, silica fume has been used as an in ingredient in concrete, most often at a percentage by weight of from 7 to 10 percent of the cement admixture within the concrete. “It has been found that silica fume improves compressive strength, bond strength and abrasion resistance, [plus] reduces permeability, and therefore helps in protecting reinforcing steel from corrosion,” says the FHWA website.
|Large-scale, noisy activities such as demolition work or concrete crushing visibly create dust and particles that are noticeable to employers, workers, neighbors and regulators.
The activities of mixed C&D recyclers may be less visible and might produce dust in overall smaller amounts, but some dust-related hazards must still be kept in mind.
On its website at www.cdc.gov, the Centers for Disease Control and Prevention (CDC) has a page pertaining to the hazards of drywall dust. While the site mentions drywall sanding as the source of such dust, when drywall enters a grinder or breaks apart in the sorting process, dust also is produced.
The CDC says workers exposed to the dust from drywall joint compounds “are often exposed to high concentrations of respirable silica.” That’s because drywall joint compounds “are made from many ingredients (i.e., talc, calcite, mica, gypsum, silica), some of [which] have been associated with varying degrees of eye, nose, throat and respiratory tract irritation. Over time, breathing the dust from drywall joint compounds may cause persistent throat and airway irritation, coughing, phlegm production and breathing difficulties similar to asthma.”
To address the problem, mixed C&D recyclers can turn to nozzle spray or mist systems mounted above or near sorting and processing equipment as well as the fan-style units used at job sites and crushing plants.
But concrete containing silica fume need not be present for a silica dust risk to exist. According to a “Silicosis Fact Sheet for Construction Workers” on the OSHA website, “Most crystalline silica comes in the form of quartz,” and “common sand can be as much as 100 percent quartz.” Therefore, according to OSHA, since “concrete and masonry products contain quartz in the form of sand, there are many ways to be exposed [to silica] at construction sites.”
In all cases where concrete is being smashed or size-reduced, demolition workers and crushing plant operators are breaking down materials with crystalline silica dust as a percentage of the particulate matter in part of the dust created.
When a worker’s lungs are over-exposed to silica-containing dust, the potential damage is substantial. “Silicosis is a progressive, disabling and often fatal lung disease,” OSHA says.
The symptoms of the disease include shortness of breath, possible fever, fatigue, loss of appetite, chest pain, a “dry, nonproductive cough,” and ultimately, “respiratory failure, which may eventually lead to death.”
Those symptoms can be signals that silicosis is leading to a list ofneven more serious health disorders, according to OSHA, including:
- Lung cancer (silica has been classified as a human lung carcinogen);
- Bronchitis/chronic obstructive pulmonary disorder;
- Tuberculosis (silicosis makes an individual more susceptible to it);
- Scleroderma, a disease affecting skin, blood vessels, joints and skeletal muscles; and
- Possible renal disease.
The potential of such health problems has caused OSHA to emphasize silica dust control monitoring. In an instruction order found on the OSHA website that went into effect in January of 2008, the agency outlines its “National Emphasis Program – Crystalline Silica.”
The instruction order, according to OSHA, “describes policies and procedures for implementing a National Emphasis Program (NEP) to identify and reduce or eliminate the health hazards associated with occupational exposure to crystalline silica.”
In the NEP document (which can be found at www.osha.gov/pls/
oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=3790), regional OSHA offices are asked to identify targeted industry sectors and companies in their regions and then “develop a master list of establishments to be inspected in accordance with OSHA instruction[s].”
SEVERAL OUNCES OF PREVENTION
The risks of breathing dust in general and silica in particular have been well-known for some time, which has enabled the demolition and recycling industries to take proper steps in response.
In both demolition and concrete crushing applications that most common of compounds— water—can be used to make the critical difference in protecting workers from breathing in too much dust.
At demolition sites, contractors can turn to a variety of equipment suppliers who produce machines that combine specially designed fans and nozzles to direct water droplets to the right places to suppress dust near its source point.
These units, when properly deployed, produce a mist that encapsulates dust particles and lets them drop to the ground before they drift into the cabs of excavators or loaders or to other places where workers are on site.
Dust suppression systems also have become incorporated into the design of many crushing units. Crushing plant operators seeking additional dust suppression capacity can turn to aftermarket suppliers of nozzles that can be mounted to machines. Additionally, they can work with the same suppliers of the fan units that are used at job sites.
In addition to suppressing dust at its sources, workers can be outfitted with personal protection equipment (PPE) to help protect their lungs from dust and particles. Facemasks can be one way of filtering out large-particle droplets. In cases where dust creation is difficult to suppress or particularly heavy, the use of respirators may need to be considered.
Finally, OSHA recommends some very standard hygiene steps for workers that can act as important silicosis prevention steps, including washing their hands and faces before eating or smoking and refraining from eating or smoking in areas where dust is in the air.
Human lungs will always be susceptible to particulates such as silica that don’t belong there. But employers can work with equipment suppliers and their workers to help ensure that this unwelcome invasion of the lungs remains minimal.