Protecting yourself from gases and fumes

Protecting yourself from fumes and gases often means overcoming objections.

Some welders mistakenly argue that running a fan to blow smoke away eliminates risk. Others avoid using protective equipment because it's uncomfortable or takes too long to set up. Worse, your workplace might not have the proper equipment accessible or in good repair.

In poorly ventilated areas, welding gases displace oxygen. Exposure to these welding fumes and gases can cause both short- and long-term health damage.

Short-term problems include dizziness, shortness of breath, unconsciousness, and, in severe cases, death. Long-term problems may include increased exposure to known carcinogens, respiratory irritation (nosebleeds, ulcers, and holes in the nasal septum in extreme cases), blood poisoning, metal fume fever, kidney and bone defects, nervous system disorders, and pulmonary edema (fluid in the lungs).

Making sure you're using the most appropriate equipment for the job at hand is essential to keeping your lungs safe (see Figure 1). Following are 10 other simple ways to protect yourself.

1. Position the Source-capture Nozzle Correctly

When using source-capture arms to remove pollutants from the breathing zone, position the arm's intake nozzle to take maximum advantage of air velocity (see Figure 2). A good rule of thumb is to position the arm nozzle within 4 to 8 inches of the weld, or within the same distance as the source-capture arm's diameter, depending on the capacity of your equipment.

The nozzle should be close enough to capture the pollutants but not so close that it exhausts shielding gases (see Figure 3). The nozzle should be on the side of the weld that's opposite you, drawing pollutants away from the breathing zone, not into your face.

Figure 1 Making sure you're using the most appropriate equipment for the job at hand is essential to keeping your lungs safe.

2. Use Backshields and Sideshields

Figure 2 These contours show the percentage of air velocity for a source-capture duct. The numbers on the left are a percentage of the size of the diameter opening in distance from the opening.

Downdraft table backshields and sideshields force air to be drawn down from the top and front of the table, where you generally are positioned. They help contain welding and grinding sparks in the area of the work surface, saving setup and cleaning time.Shields also allow more than one worker to use a table without distraction and protect others from inadvertent welding light hazards.

3. Contain Robotic Welding Space

Robotic welding, because of the quantity and speed of welds, generates a significant amount of smoke. To handle that level of fumes, use welding screens to limit the volume of air that must be captured. This step could mean the difference between concentrated cleaning of the 1,000 cubic feet of dirty air and trying to clean 800,000 cubic feet of less problematic plant air.In addition to the welding screens, place an exhaust hood directly above and close to the welding station.

4. Limit Fan Use

Figure 3 A source-capture nozzle placed too far from the workpiece (right) causes welding fumes to remain in the breathing zone. When the nozzle is correctly placed (left), welding fumes are exhausted directly into the arm, away from the welder's breathing zone.

Welders sometimes make the mistake of using fans to blow welding smoke away from the workspace—effectively making the smoke everyone's problem.

In clean-air booths, some welders aim a fan into the booth in an effort to augment the cleaning. Actually, this decreases efficiency and disrupts airflow within the booth, exposing you to pollutants that would otherwise be drawn directly into the booth's filter area. The fan also might blow smoke out of the booth, adding pollutants to ambient plant air.

Some clean-air booths are equipped with an air regain system (see Figure 4), which washes the breathing zone with a controlled, even sheet of clean air, without diffusing smoke within the booth.

5. Watch Turns per Hour With Ambient Air

Figure 4 Air regain systems in clean-air booths wash the breathing zone with a controlled sheet of clean air.

For plants that augment source-capture equipment with ambient air cleaning equipment, the most important consideration is the number of "turns"—the number of times the equipment processes the plant's volume of air—per hour. The turn rate can be increased with proper placement of air cleaning equipment, correct equipment capacity, and other variables. Between six and 12 turns per hour generally is acceptable for a moderate to heavy load.

It is best to have a professional evaluate your facility to determine the equipment you need. However, you can use the following equation to calculate the cubic feet per minute (CFM) of air processing you'll need to make the necessary air turns:

Required CFM = (Length of room XWidth of room XHeight of room XNumber of turns required)/60

As an example, in a room measuring 100 by 50 by 15 ft., you can achieve eight turns per hour by using equipment that can clean 10,000 CFM of dirty air.

6. Use Equipment That Requires No Setup

The best way to shorten setup time for source-capture air cleaning equipment is to have no setup at all. Whenever possible, use clean-air booths, downdraft tables, backdraft hoods, or overhead hoods. That way, you need only to grab the part, place it on a table, and get started.

7. Ventilate the Tight Spots

Welding under heavy equipment, in tight corners, or in difficult-to-reach places makes it easy to avoid the safety equipment that is needed most in these areas.

Figure 5 Where typical air cleaning equipment can't reach, portable units with flexible hoses keep welders breathing easier.

Downdraft tables, hoods, and the like can't help you in a tight spot, and source-capture arms are limited in reach. An air cleaner equipped with a flexible hose is suitable for these situations (see Figure 5).

8. Use a Clean-air Booth for Flexibility

Welding a small part and welding a canoe require two vastly different approaches to ventilation safety—unless a clean-air booth is used.

Clean-air booths can be modular, allowing you to combine multiple booths for large, small, and multiple projects. You can turn on just one booth for a small part or additional modules to obtain coverage for larger parts. Again, faster setup means safer welders.

9. Put Multiple Parts on a Revolving Table

Rather than moving a source-capture arm every time, consider using a revolving table. It allows you to place an arm in a single position while rotating workpieces. Often multiple welders use the same revolving table simultaneously.

You can make a hand-rotated assembly by mounting a work surface to a bearing. Several motorized models and high-end rotating workcells also are available.

10. Perform Regular Maintenance

If safety equipment isn't working properly, you might as well have none at all. Dirty, plugged cartridge filters impair air cleaning. Blocked hoses decrease efficiency and increase wear on fans and motors. Lowered air pressure prohibits the filter cleaning system from working properly.

A quick, daily check of the cartridge filters, hoses, and system operation solves most problems before they occur. Replace worn or blown-out filters quickly, and clear or replace clogged hoses. To save costs on filter replacements, make sure your equipment has an efficient cartridge cleaning system.

A Magnehelic® gauge provides a quick, simple way to check air cleaner system efficiency. The gauge measures pressure difference across cartridge filters; the bigger the difference, the more clogged the filters. For accurate readings, use a wax pen to mark the gauge's optimum reading, and compare the needle reading to the wax mark at various times during the workday.

Jerold Jay is a design engineer for the Micro Air® Clean Air Systems product line manufactured by Metal-Fab Inc., P.O. Box 1138, Wichita, KS 67201, 316-943-2351, fax 316-943-2717, info@metal-fabinc.com, www.microaironline.com.