If your company plasma or laser cuts, take a long, hard look at its ventilation practices
June 29, 2009
A shop owner should want the best ventilating technology for its thermal cutting operations. It keeps employees safe and protects the company from potential liability situations. With that in mind, the feature poses five questions that every shop should ask itself about its ventilating efforts as it regards thermal cutting operations.
For a ventilation system connected to a thermal cutting machine to function properly, it is best that the equipment is placed away from open shop doors and standing fans. A moderate breeze can overpower the ventilation effort very quickly.
However, another reality is that today's fabricating shop barely resembles its predecessor 10 or 15 years ago. Back then cutting, stamping, and welding were done in separate facilities; now they commonly occur under the same roof. Each process has its own environmental issues that, if separate, are challenging enough from a ventilation standpoint, but combined can exacerbate the others' problems.
For example, imagine a situation in which a collector dedicated to removal of thermal cutting fumes is also pulling an oil mist-saturated air stream from a nearby press, while simultaneously the ventilation equipment for the press is having to cope with the thermal cutting fumes. Varying degrees of failure are sure to occur. Keeping each process and particulate separated from the other is critical.
In all likelihood, many shops have made the investments to ventilate welding fumes. The media has publicized the ongoing legal challenges for the welding industry brought by plaintiff attorneys looking to link exposure to welding fumes with illnesses such as Parkinson's disease. So companies have to know that they need to protect their welders as much as they can.
The same can't be said for thermal cutting activities. Both laser and especially plasma cutting are arguably the largest producers of pollution in any facility. In the case of lasers, the machines need a clean environment to operate at optimal levels. Whereas a plasma cutting machine can run endlessly in a heavily saturated environment, the operator running the equipment cannot; fumes will overwhelm the operator in a matter of minutes. The fumes need to be ventilated at the source of production before they can migrate elsewhere.
If you are now thinking about your thermal cutting operations and the accompanying ventilation needs, that's good. Proper ventilation is an often-overlooked aspect of metal fabricating. The following five questions are ones that every shop should ask itself about its ventilating efforts regarding thermal cutting operations.
Simply put, a company should be concerned about its employees and capital equipment. That concern should extend to the work environment, which can be polluted with large amounts of particulate generated from thermal cutting activities.
Think about it. If you have a 260-amp power supply that's processing a 3/4-inch, 4-foot by 8-foot sheet without proper filtration equipment, a 200,000-sq.-ft. facility would fill with particulate before the cutting was finished on that one plate. The indoor environment actually would be worse than a welding shop that fails to ventilate its fumes.
If your company has invested in filtration equipment in the past, has it kept up with the latest upgrades in technology? Power supplies can generate 400 amps of power today; these higher amperages allow for faster cutting speeds and thicker materials. Cutting tables that used to have a single head now have multiple heads. With the advent of technology such as rack-and-pinion drives, gantries move much more quickly than they did in the past. All of this results in faster and more productive cutting, which means much more metal cut per hour and greater fume generation as well.
Tables are much larger today as well; one table in the Midwest is 300 ft. long. Was the filtration upgraded with the new, larger table?
Of course, liability needs to be discussed as well. Exposure to certain compounds may not be a problem today, but may well be a problem tomorrow.
For example, manganese exposure likely will become more tightly regulated in the near future. The gray-white metal, which resembles iron, is widely used in steelmaking, particularly in stainless steel formulations and certain aluminum alloys. Overexposure to the element has been linked to nervous system damage in humans.
The potential risks linked to manganese exposure are not recent discoveries. Manganism was coined in the late 19th century to describe Parkinson's disease-type symptoms found in miners and smelters who had been exposed to manganese. Burgeoning class-action lawsuits are the new developments that have opened the eyes of metal fabricating management to realize the need for good filtration of thermal cutting activities.
Right now the Occupational Safety and Health Administration (OSHA) standard for permissible exposure limit (PEL) to manganese fume is 5 mg/m3, which is based on an eight-hour time-weighted average. The threshold limit value for manganese, determined by the American Conference of Governmental Industrial Hygienists (ACGIH®), a collection of occupational and environmental health professionals and safety officials, is 0.2 mg/m3. ACGIH's recommended exposure limit is 25 times lower than OSHA's requirement at this time. This numeric guidance should be noted because ACGIH limits often heavily influence OSHA when the time comes for revisiting PEL standards.
For those who are skeptical that OSHA would enact such a dramatic change in PEL standards, they only have to look back at the new standards for hexavalent chromium. The new OSHA PEL is 0.005 mg/m3 per eight-hour time-weighted average. This is down from the previous PEL of 0.052 mg/m3 that existed prior to February 2006. This is a reduction of 10.4 times the previous established PEL.
Don't rely on educated guesses. Don't rely on the manufacturer of fabricating or ventilating equipment. Hire a third-party inspection firm, such as Bureau Veritas or any accredited AIHA (American Industrial Hygiene Association) professional.
For a fee, the company will come in and set up monitors throughout your facility and on selected employees. Over an eight-hour period, the monitors gauge air quality. Upon completion of air monitoring, the company inspects the air filters and analyzes the contents. From that, areas of concern can be identified in the facility and discussion of remedying the situation can begin.
If you're worried about your company having to pick up the tab for such testing, contact your insurance company or state OSHA entity. Insurance carriers should be interested in helping you take steps that protect your company from having to cover huge payouts if something goes wrong in the future. For Michigan companies, the state's version of OSHA has a Consultation, Education, and Training Division that can assist with monitoring equipment. Check with your state entity to see if a similar program exists.
Because of the sheer volume of particulate being produced in a thermal cutting operation, a self-cleaning cartridge collector is a good choice. The filters, which are designed to filter particles as small as 0.5 micron, are capable of keeping up with the large amounts of particulate generated by cutting machinery. It is not uncommon to generate 55 gallons of material in a single day while thermal cutting; welding may take months to produce the same quantity of particulate.
The key to the successful removal of particulate is air-to-cloth ratio. For thermal cutting operations, that means 1-to-1:1 sq. ft. of filter media for a 1-cubic-ft.-per-minute (CFM) application.
For more aggressive environments where a shop might be cutting really thick metal and having longer periods of uptime, that ratio is 0.5-to-1. So a shop with a 2,000-CFM application would need 4,000 sq. ft. of media to stay on top of the cutting.
You might opt for a 1.5-to-1 or a 2-to-1 ratio to minimize initial investments, but the cartridge filters are going to load much faster as they struggle to keep up with the cutting. As a result, the maintenance person is going to have to replace filters much more frequently, and the shop floor will have to schedule breaks between individual sheet cuts so that the cartridge filters have a chance to shed particulate with controlled pulses.
For a cartridge filter to have a nice, long life—six months to a year—the particulate matter has to get out of the pleat and into the collection device. This is accomplished with a periodic back-flush of compressed air that is sent through the filters, clearing them of particulate, which then falls into a bin for disposal.
So time has to be allotted for "pulsing" to occur. If filters load up and airflow decreases, the performance of the entire system is compromised. The only options available at this point are immediate maintenance of the collector to restore proper airflow or replacement of the filter elements.
Replacing filters can turn into a costly exercise. If filters have to be replaced every six weeks, you run the risk of spending several thousands of dollars, depending on the system size, of course, annually.
If your metal fabricating shop cuts aluminum, you should realize the danger that aluminum dust presents.
Aluminum is a reactive, flammable solid. Bulk aluminum metal is not combustible, but the hazard increases as the aluminum particle size decreases.
Aluminum dust in contact with water may heat spontaneously. The reaction between the two substances creates flammable hydrogen gas as a byproduct, which can create a very dangerous explosion, particularly if the fire occurs in a confined area.
Aluminum dust that results from laser cutting operations that use nitrogen as an assist gas is especially risky because it's pure aluminum. Aluminum cut without nitrogen turns the aluminum into an oxide, which is not as dangerous.
A mixture of aluminum and steel dust also can create a problem. The steel dust can act as an ignition for the aluminum dust and trigger an explosion.
That's why it's important that ventilation equipment have spark arrester controls and explosion vents if your shop is going to process multiple metals on the same equipment. Some metal fabricators actually have two dust collectors with a converter valve for aluminum and steel cutting, but that setup is still rare.