3With colder weather approaching, now is the time to re-evaluate how you go about controlling the dust and fumes generated during welding. Some of the commonly used “remedies” to fume buildup can be problematic. A proper ventilation system that utilizes a high efficiency dust and fume collector and recirculates clean air through the shop is a proven way to keep fumes under control in winter months while providing a good return on investment in energy savings.
Why not just open the shop doors periodically to allow fumes to escape? A fume cloud can build up rapidly in an enclosed facility, especially if a high volume of welding and cutting is taking place. This can necessitate leaving doors open much of the day, creating a cold and uncomfortable indoor environment where workers are bundled up in heavy clothing. Most of us have witnessed this scenario. It can be physically difficult for welders and others to perform their everyday tasks, and it can potentially lead to illness.
As a side note: If you do opt to release fumes outdoors, winter or summer, and you consume more than 2,000 lbs. of welding wire in a year, the air exhausted from your facility is subject to stringent monitoring under EPA NESHAP Rule 6x. The required monitoring and test procedures are rigorous; but simply stated, in any 20-min. test period there can be no more than three minutes of visible emissions (zero opacity) from the process.
Installing exhaust fans is another common approach for removing dirty air from shops. Exhaust fans are often large, noisy and energy-intensive, and they don’t always do the best job of removing dirty air. Often they are used with no regard to providing replacement air into the facility, and when the doors are closed, a negative pressure condition results.
Excessive negative pressure is a safety no-no, as it can cause injury to occupants from doors slamming shut and can make it very difficult to open doors in an emergency. This condition also allows cold air to seep in through any cracks or weak spots in the structure, creating drafts and increased demand for heaters.
Following accepted ventilation practices, facility air should be neutral or slightly pressurized; and a prescribed percentage of outside air should be conditioned to deliver clean air to occupants at comfortable temperature and humidity levels. In an office building, a good HVAC system with proper filtration accomplishes this goal quite effectively. However, this approach is not sufficient to clean the air of welding fumes or the other heavy contaminants generated in industrial environments.
How much fume is too much?
The leading indicators that you have an air quality problem are:
- Visible fumes and dust: Some degree of visible fumes is inevitable during welding; but if the cloud grows denser and denser throughout the day, and a blue haze lingers even during breaks, there is probably an issue.
- Worker complaints: Welders complaining of health and discomfort problems are likely being exposed to an excessive level of fumes. Fumes are linked to an array of short- and long-term illnesses and adverse health effects from chronic headaches and fatigue to cancer and respiratory diseases. Complaints should always be taken seriously and addressed as promptly as possible.
- Failure to meet established air quality standards: Air quality testing using air sampling techniques is often performed to ensure that a shop is in compliance with OSHA regulations. OSHA has established permissible exposure limits (PELs) based on 8‐hour time weighted average for hundreds of dusts, including the numerous metals contained in welding fumes. By the time a shop fails an air quality test, heavy fume clouds and worker complaints will already be in evidence.
Cartridge dust and fume collection
A well-designed cartridge dust and fume collection system properly filters welding fumes and other hazardous contaminants, and the filtered air can be exhausted outside or recirculated back into the facility for significant energy savings. These systems use self-cleaning mechanisms that pulse dirt off the filters, allowing units to run for extended periods between filter changeouts.
If you already have a fume collection system and are still experiencing unacceptable fume levels, it may be that you’ve outgrown the system because of increased production, it was improperly sized at the time of installation, or the equipment is malfunctioning.
Whether you are installing a new fume collector or updating an existing system that is no longer adequate, there are three general types of fume collection systems to choose from. Source capture systems that utilize flexible arms are popular for applications involving small parts and fixture welding. Booths, curtains, or custom enclosures with overhead hoods form a middle ground between installing a new fume collector and updating an existing system by isolating a specific area for fume collection. Ambient systems that filter all the air in the shop using a central system or multiple smaller collectors are used to serve larger areas, allowing a facility to vary its operations and still capture fumes.
With all three types, the fume collector typically utilizes high efficiency pleated filter cartridges treated with a flame resistant coating. In hazardous applications, the collector may require HEPA secondary filters (also called after-filters) for added filtration and backup protection. Secondary filters are also recommended if you opt to recirculate the filtered air instead of exhausting it outside.
Air recirculation during the cold weather months is the single best way to save energy and maximize return on investment with a fume collection system. Recirculating heated air back through the plant instead of venting it outdoors provides a multitude of savings. The cost to replace the air is eliminated, the cost to heat the replacement air is minimized, the re-utilizing of all heat sources within the area saves energy and blending the warmer air at the ceiling back into the space for a more even temperature at the floor level lowers heat loss and saves energy.
Facilities report five- to six-figure annual energy savings with air recirculation, with the greatest savings in northern climates. In addition, the U.S. Department of Energy offers public utility-sponsored rebates and incentives for facilities that use recycled heated or air conditioned air.
On a related note, many factory floors are cold in the winter – even in a heated facility where the doors are closed. The reason, quite simply, is that heat rises to the high ceiling, leaving a chilly environment for workers below. A recirculating ambient fume collection system can eliminate this problem and help make factory environments more comfortable in winter due to the redistribution and recirculation of the heated air.
Another approach is to use a summer/winter diverter. A damper-operated split in the ducting allows clean air from the fume collector to be blown outside in the summer or inside in the winter. In the winter position, the system provides three primary benefits. First, it balances pressure in the facility by ensuring that the volume of air drawn out of the shop equals the volume that is returned. Second, it provides heat recovery by returning clean air to the facility so no added heat is required, saving energy. Third, designed properly, it can enhance the efficiency of the collector by using the recirculating clean air to push and direct the fumes so that they are more efficiently captured and filtered out.
Example of Air Recirculation Advantages
A manufacturer of desiccant dehumidification systems was experiencing problems with fumes in its high bay welding and fabrication shop. The area contained eight welding booths approximately 20 ft. by 20 ft. in size, open at the top with a ceiling height of about 26 ft. and an overhead crane above. Because the equipment being manufactured is large and irregular in shape, there was no way to do point source capture of fumes. The shop had to rely on overhead exhaust fans blowing fumes directly outdoors. The fans did a poor job of capturing the fumes and they wasted energy by blowing heated air out the window.
To solve the problem, the facility installed a cartridge dust and fume collection system with 16 high efficiency filters. By designing the system to recirculate filtered air back through the facility, the company determined through a heat recovery calculation that it would be able to save $35,000 yearly in heating costs. In addition, the equipment supplier submitted the savings calculations to the local utility, which gave the facility a sizeable grant to help offset the cost of the project.
The key benefits achieved by this manufacturer, which are translatable to many other applications, include a rapid payback in equipment investment costs, five-figure or higher annual energy savings, and an immediate and significant improvement in air quality. While the delivery of clean air is not strictly quantifiable in dollar amounts, it is priceless in that it safeguards the health of employees, improves morale and productivity, and ensures regulatory compliance.