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Unseen Killer: Industry Looks Into Alternate Methods to Prevent Silicosis

Sat February 10, 2001 - West Edition
Pete Sigmund

An unseen killer still stalks the construction industry.

Day after day, this assailant slowly stifles his victims as they jackhammer concrete, sandblast steel rebar, saw through or demolish masonry, and perform many other tasks.

The killer’s name is silicosis, which permanently scars and hardens lung tissue over time as the victim breathes dust containing extremely fine — less than 10 micrometers in diameter — particles of crystalline silica. This dust is too small to be seen with the naked eye.

Construction workers are now the No.1 prey of silicosis, with mining number two.

The disease is nonreversible and often fatal. Surgeons sometimes find that the lungs of victims are so hardened by accumulated dust that they can scarcely be pierced with a scalpel.

Silicosis in construction has been occurring so long and so often that the National Institute of Occupational Safety and Health (NIOSH) issued an alert in 1996 warning that “exposure to respirable crystalline dust during construction activities can cause serious or fatal respiratory disease.”

When workers inhale the unseen particles, it said, lung tissue reacts by developing fibrotic nodules and scarring around the particles. This fibrotic condition is silicosis. When the nodules grow too large, breathing becomes difficult and death may result. Victims also are at high risk for active tuberculosis. And, since the disease destroys blood vessels that run through the lung, it’s also associated with heart disease.

Initially, workers may have no symptoms. As the disease progresses, however, it may cause difficulty in breathing, and chest symptoms like coughs.

Infectious complications may cause fever, loss of weight, and night sweats.

NIOSH said workers may develop any of three types of silicosis: chronic, after 10 or more years of exposure at relatively low levels; accelerated, after five to 10 years exposure to high concentrations; and acute, from the highest exposure concentrations from weeks to four or five years after initial exposure.

Crystalline silica is the second most common mineral in the earth’s crust and is found in concrete, masonry, rock, aggregates, mortar and other construction materials. The U.S. Department of Labor estimates that more than one million workers are exposed to silica dust on the job and about 100,000 of these are “at a high risk” of developing silicosis, which kills at least 250 workers a year. An increasing number of these workers are in construction as this industry continues to expand.

NIOSH warns that “evidence indicates that crystalline silica is a potential occupational carcinogen.”

Whether you are building a concrete highway, drilling rock for asphalt, or preparing a bridge for painting, you are a potential victim.

Yet many forget the killer.

“Silicosis doesn’t happen overnight, and it’s not in the forefront of workers’ minds,” said Ken Linch, industrial hygienist with the Division of Respiratory Disease Studies of NIOSH. One of the nation’s leading authorities on silicosis, Linch studies the disease at the division’s headquarters in Morgantown, WV.

“Unfortunately, a lot of construction workers aren’t trained to wear proper respirators, and many contractors have never even heard of silicosis,” Linch told Construction Equipment Guide. “Our first priority is prevention, removing the hazard. If you can redesign equipment to produce less dust, you make it more likely that respirators will protect workers. But we’ve found that concrete dust levels in activities like drilling holes for anchoring steel rebar in concrete are sometimes 10 or 15 times the OSHA [Occupational Safety and Health Administration] limit.”

Linch told CEG that death certificates from 18 states indicate that silicosis occurs in construction more often than in any other industry and that more construction workers die on the job than any other field.

“A couple of years ago, mining was ahead of construction [in deaths]; now construction is ahead of mining,” he said. “One reason is that there are more workers in construction as the country spends more on infrastructure. I believe that the estimates of 250 deaths a year are probably too conservative.”

One of the greatest U.S. industrial disasters of all time involved silicosis. At least 400 and perhaps as many as 2,000 construction workers, mostly migrant African Americans, died from the disease after helping dig a hydroelectric tunnel below the Hawk’s Nest Gorge on the New River in West Virginia between 1930 and 1932.

Myriad construction activities expose workers to the killer dust. One is abrasive sandblasting using silica sand as the abrasive. The dust from the sand is bad enough; the air is even worse when the material being worked on is concrete, which itself has sand or other aggregates containing silica.

Contractors sandblast concrete during maintenance of old bridges; they also sandblast steel for new bridges (to remove rust), and use this abrasive technique to prepare expansion joints in concrete highways before applying sealant, and to remove lane-marker paint from these highways. Architects sometimes specify light sandblasting to give texture to new buildings.

NIOSH is now testing alternatives to sand as abrasive material.

Sawing concrete also can be dangerous. Repairing potholes, for instance, usually requires sawing out a rectangular area in the concrete so the area can be jackhammered before placing new concrete. Linch said contractors often fail to apply water, which protects against dust, to the saw-blade for this task.

“A lot of times they will saw dry, particularly if it’s a busy area,” he said. “They don’t want water on the pavement or in the hole. Workers also can breath silica dust when they saw out expansion joints in new concrete highways after the concrete sets. Though this is a better situation because the fresh concrete still contains water, applying water to the blade reduces but doesn’t remove all the dust.”

“Equipment manufacturers need to be more aware that sawing any kind of concrete or masonry while dry can produce a tremendous amount of dust,” Linch added. “Power equipment increases productivity but also produces a great amount of sand. Contractors depend on manufacturers to stay within the legal limits. A lot of equipment does have dust controls, but often only as an option, and whether these controls work well is questionable.”

Linch said jackhammering or drilling, as well as sawing, during new construction or to change existing construction, can also produce the silicon dioxide dust. So can drilling blast holes at construction sites, which exposes the drill operator and helper to perhaps the most dust of any activity since drilling is a pulverizing activity.

In a special alert to construction workers, NIOSH also warns of these other activities that produce silica dust:

• Chipping, hammering, drilling, crushing, loading, hauling and dumping rock;

• Demolishing concrete and masonry structures; and

• Dry sweeping or pressurized air blowing of concrete or sand dust.

Even materials containing small amounts of crystalline silica may be hazardous if they are used in ways that produce high dust concentrations.

“There are so many ways to goof up,” Linch told CEG. “The victims often work for smaller contractors, Mom and Pop operations who are subs for jobs.”

How can contractors and workers prevent silicosis?

OSHA said that, “The key to silicosis prevention is to prevent dust from being in the air.” A simple, often-effective control, is wetting dust down, at the point of generation, with a water hose. The agency also recommends:

• Always use the dust control system and keep it in good maintenance.

• When sawing concrete or masonry, always use saws that provide water to the blade.

• During rock drilling, use water through the drill stem to reduce dust in the air.

• Use abrasives containing less than 1-percent silica during abrasive blasting to prevent harmful quartz dust from being released in the air.

• Measure dust levels in the air.

Both OSHA and NIOSH stress that respirators should not be the primary method of protection and should only be used until adequate dust controls are in place, or if controls cannot keep dust levels below recommended levels. They also recommend periodic medical exams, including chest X-rays, for all workers who may be exposed to respirable crystalline silica. Informing workers of the danger, and training them in safe working practices, also is essential, and is frequently being done by unions.

OSHA standards limit the amount of dust which workers can be exposed to, and also set requirements for respiratory products. Sources indicate that the agency is working on new standards for monitoring workers’ medical condition and for monitoring the air at worksites. The existing sampling standard, dating from the 1960s, is considered obsolete.

The standards, expected to be proposed this year, would require training workers and sampling the air to make sure they can perform while wearing respirators.

Rather than telling contractors how to do the job, OSHA reportedly prefers to have the standard set the permissible amount of dust in the air, and then allowing contractors to come up with solutions.

(A group of 17 companies and organizations called the Silica Coalition is supporting its own studies of the link between silica exposure and silicosis, saying this will ensure that OSHA’s exposure limits are accurate. The group includes the American Road and Transportation Builders Association in Washington, D.C.)

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