Control of Airborne Particles

The responsibility of today's maintenance and engineering managers to maintain a clean indoor air environment has increased markedly in recent decades.

• By Bruce Prather
• Oct 01, 2009

Since classical times, airborne particles have been identified as potential health hazards. With the rise of modern science, medical scientists have demonstrated the relationship between the chemical and physical characteristics of airborne particles and respiratory diseases. News reports chronicling the scientific findings have increased public awareness of air quality issues and led individuals to pay closer attention to the airborne particles in their workplaces.

Generally, airborne particles are categorized into three main types:

1. Large particles. Particles greater than 100 microns in diameter are considered large. These particles fall quickly and include such things as hail, snow, room dust, and soot aggregates. Although they can cause irritation to the eyes, nose, and throat, large particles are not fine enough to reach the lungs.

2. Medium particles. Particles that lie between 1 and 100 microns in diameter are considered medium-sized. Settling slowly, these particles consist of pollen, large bacteria, coal dust, as well as dust produced during industrial processes, including welding and grinding. These particles pose the greatest health risk because they are able to pass through the nose and throat and penetrate the gas exchange region of the lungs, where they settle.

3. Small particles. Small particles are less than 1 micron in diameter and also pose serious health risks. They can be washed out by water and rain and include viruses, small bacteria, metallurgic fumes and dust, as well as paint pigments.

Industrial workers are exposed to hazardous airborne particles on a daily basis. Given that there are an estimated 400,000 workers in the welding industry alone, it is important to understand the potential health consequences of particle inhalation.

Health Concerns
Airborne particles pose a variety of health concerns to workers in the welding industry, including:

• Increased risk for developing lung cancer
• Damage to nose, throat, and lungs
• Metal fume fever

It has been well documented that long-term exposure to the fumes that welding on metals (such as stainless steel, high chrome alloys, and chrome-coated metals) produces can lead to an increased risk for developing lung cancer. As the most serious potential health concern, lung cancer begins with changes in the lungs caused by exposure to carcinogens. These changes are characterized by the development of abnormal cells on the lining of the bronchi (breathing tube) that multiply with increased exposure and eventually become cancerous, progressing into a tumor. Symptoms of lung cancer include chronic cough, hoarseness, chest pain, shortness of breath, and repeated episodes of bronchitis and pneumonia.

The inhalation of known welding byproducts such as hexavalent chromium also can damage or irritate the nose, throat, and lungs. Larger airborne particles deposit in the nose and throat, contributing to coughing and sore throat, and may be eliminated by sneezing or blowing one's nose. Smaller particles, however, collect in the tiny air sacs of the lungs, causing inflammation and swelling of the blood vessels.

Metal fume fever is an acute allergic condition that affects many welders throughout the duration of their careers. It is caused chiefly by exposure to zinc oxide, another welding fume, and produces flu-like symptoms. Welders afflicted by metal fume fever may experience headache, fever, chills, muscle aches, thirst, nausea, vomiting, chest soreness, gastrointestinal pain, and weakness. These symptoms can last anywhere from six to 24 hours; complete recovery can usually be expected within 48 hours.

Control Methods
In light of these airborne health hazards, a number of control methods have been created to limit workplace exposure, including air ionizers, fume arms, and downdraft tables.

Air ionizers operate by creating negative ions and changing the polarity of airborne particles. By changing polarity, particles magnetically attract together, becoming too large to remain airborne and as a result falling out of a worker's breathing zone.

Fume arms, or lab hoods, are another option. These units are typically self-contained, 8- to 12-foot arms (snorkels) attached to a filtration system that can be moved from location to location. In order to absorb airborne particles, the arm is placed over the workstation, drawing up fumes and smoke.

Finally, downdraft tables are self-contained units that draw air from the workplace in a downward direction through perforated tabletops. They maintain a powerful suction in an open workspace as the filtration system filters dust, fumes, and smoke away from operators' breathing zones. Downdraft units also exhaust clean air back into the workplace.

Important Considerations

Employers seeking to improve workplace air quality and acquire the appropriate equipment for their needs undoubtedly face a difficult task. Though a complicated process, the following considerations can help ensure that both employer and worker interests are met:

• What emissions need to be captured, and what filtration options are the most effective for each situation?
• Should a ventilation system be self-contained or integrated into the existing HVAC system?
• Is there a need for a source capture filtration system?

It is important to first review the emissions that need to be captured and the available filtration options. Depending on the air quality issue at hand, different filters may be needed to accomplish the desired effect. Fumes from glue and paint, for instance, are often best absorbed by carbon filters. These filters are available in weight increments of 2, 6, 12, and 30 pounds. Dust particulate and smoke particles, however, usually require two- to three-stage filter packs. The first of these filters is a pre-filter, Minimum Efficiency Reporting Value (MERV) 8 to 11, which is 40 percent efficient to the submicron level, followed by a MERV 14-15, 95 percent efficient to 0.7 microns, and, finally, in those instances where the finest airborne particles are present, a High Efficiency Particulate Air (HEPA) filter may be needed, boasting a 99.97 percent efficiency rate to 0.3 microns.

When deciding whether or not a ventilation system should be self-contained or integrated into the existing HVAC system, it is important to consider the volume of air being circulated. Most air cleaning equipment will generate 1,000 to 3,000 cubic feet of air per minute; if the system is not self-contained, this air will need to be replaced with heated or cooled air. In an eight-hour shift, approximately 960,000 cubic feet of air will need to be heated or cooled in an integrated system, an additional cost that must be calculated.

Source capture filtration systems capture contaminants as they are occurring at the work site. Many professionals prefer this method of filtration because it does not allow airborne particles to disperse and potentially endanger workers before absorption.

Because of the individual challenges each air quality problem presents, no one ventilation system can provide a universal solution. The complexities of these situations may even be such that the expertise of an air quality specialist or hygienist is needed.

Employees Highly Informed
The responsibility of today's maintenance and engineering managers to maintain a clean indoor air environment has increased markedly in recent decades. Employees are more concerned about health, they are more aware of allergic conditions, and they have become increasingly informed about the adverse effects of hazardous airborne particles. Faced with the substantial complexities of improving air quality, these professionals should carefully consider their workplace needs and available options and act on this knowledge. Doing this will help increase the health and efficiency of both workers and their workplaces and ensure ever-increasing regulatory compliance in a constantly changing industrial world.