Guns for safety
- April 9, 2013
by Dan Weimer
Understanding fume extraction guns and the critical role they play in safe welding practices
Regardless of the welding process used, maintaining the appropriate safety procedures is critical. From wearing the proper welding helmet to other personal protective equipment — flame-resistant gloves, a long-sleeved jacket and appropriate footwear — each item keeps employees safe from the heat and electricity generated by the arc. It also helps maintain a higher level of comfort, making it easier for welding operators to weld for longer periods of time.
Providing welding operators with the proper ventilation during the welding process is also essential. The Occupational Health and Safety Act (OHSA) and other safety regulatory bodies have set standards for the levels of allowable exposure limits of welding fume and other particulates (including hexavalent chromium). For some companies, using a fume extraction gun (in conjunction with a fume extraction device or filtration system) is a viable option for maintaining both compliance with these regulations, and keeping welding operators safe and comfortable.
Fume extraction guns are available in a variety of amperages (typically 300 to 600), cable styles and handle designs, and like all welding equipment, they have their best applications, advantages and limitations.
Applications for fume extraction guns
Fume extraction guns are beneficial for welding in confined spaces, where the goal is to capture fumes immediately at the source — in the welding operator’s breathing zone. Industries where these applications occur include heavy equipment manufacturing and shipbuilding. General manufacturing and fabrication applications with mild or carbon steel may also present the opportunity to use a fume extraction gun, as can petrochemical or other applications where stainless steel welding and greater hexavalent chromium levels are prominent. The guns also work well on high amperage and high deposition rate applications.
Some companies choose fume extraction guns with a localized filtration system in lieu of a more intricate and expensive centralized fume extraction system, which involves the installation of ductwork throughout the shop area.
Regardless of the application, it’s a good idea to modify other aspects of the welding operation (filler metals, base material, transfer methods, etc.) to help minimize fume rates, too. Doing so adds to the safety and comfort of the welding environment brought forth by using a fume extraction gun.
General operation of fume extraction guns
Every fume extraction gun manufacturer designs and produces its product to operate in a different manner. As a general rule, however, fume extraction guns operate by way of mass flow, the movement of material initiated by a vacuum chamber in the fume extraction gun. The vacuum chamber suctions the fumes through the handle of the gun, into the gun’s hose through to a port on the filtration system. These filtration systems are sometimes referred to as a vacuum box or a fume extraction system. The welding fumes that these guns remove are composed of a combination of the filler metal and base material, and their removal by the fume extraction gun occurs right at the source, over and around the weld pool.
As with the specific manner in which fume extraction guns operate, features on these guns are often unique to individual manufacturers. Some fume extraction guns feature adjustable extraction control regulators at the front of the gun handle. These regulators allow welding operators to increase suction as needed, without affecting shielding gas coverage. Other manufacturers may offer the same function, but it is internal to the gun. In both instances, the gun creates a balance between the shielding gas and the suctioned air. The combination protects the weld pool from defects like porosity, while also eliminating fumes to protect the welding operator. It allows the weld pool time to react and solidify, and gives the fume particles time to decelerate so they are easier to extract.
Differences between MIG and flux-cored guns
In addition to offering fume extraction capabilities, fume extraction guns differ in other ways from their counterparts, MIG and flux-cored guns. As a general rule, fume extraction guns are larger than these other guns. They also tend to be bulkier as a result of the vacuum and hose that are responsible for extracting the fumes. To facilitate the manoeuverability of fume extraction guns, some manufacturers have found ways to engineer internal components to minimize the handle weight and/or have added a vacuum hose swivel on the rear of the handle that allows the welding operator to change angles more readily.
Advantages and limitations
For fume extraction guns to work to their greatest capacity, they should be used for in-position welding, such as on flat butt welds. In this position, these guns offer the distinct advantage of removing the fumes at the source, minimizing the amount that enters the welding operator’s immediate breathing zone. Welding out-of-position limits the ability of the gun to suction the fumes downward and through the vacuum hose (i.e., as the fume particles are rising overhead).
Also, because welding operators typically move the gun away from the weld pool after completing a pass, the fume extraction gun is not able to control residual fumes. For that reason, some companies may prefer to install a fume extraction hood, trunk style extractor or a centralized system.
Whichever the equipment decision, working with a trusted welding distributor, certified industrial hygienist and/or the fume extraction gun manufacturer can help address any questions or concerns, and put companies on the right path to a safer, more comfortable welding environment. SMT
Dan Weimer is an engineering lab technician with Bernard, Beecher, IL.