How to choose between an ambient system and a source capture system

May 2017 - We frequently get asked for advice about the best type of system for weld fume management. These requests come from companies with as few as 20 welders to those with more than 100. Many of them  face the same dilemma: Will an ambient system or a source capture system work better in our facility?

In an ideal situation, welders would always have a source capture, such as a portable collector, fume arm or a hood, at their work area. A source capture is the most effective way to prevent exposure to fumes. There’s only one problem with this: welders do not use source captures. 

In some facilities, welders work in a booth where they remain in one location. For this type of work, a hood is very effective. In many facilities, though, the pieces being assembled stay in one place, while the welders move from cell to cell. This means that as they move, they need to take the portable collector or fume arm with them to each work station. 

Ideally, welders would always have a source capture at the site where they are welding. But when we visit facilities, that is not what we see. Fume arms, hoods and portable collectors are almost never used as directed. They don’t get positioned where they ought to be, welders don’t move them to the next work cell and, as a result, source capture methods are not doing their job.

Why is it so difficult to use the source capture techniques? Fume arms and other source capture methods are inconvenient and time consuming. They have to be dragged along and repositioned constantly, and they often get in the way of the work itself. Moving them interrupts and distracts welders. Every time we visit a facility with this type of system, we see that it is not being used properly. 

Measuring for exposure to fumes usually involves testing the air directly around the welder as he or she works. If you test for a short-term exposure limit (STEL), measured over a 15-minute period, the welder under the source capture would have a lower exposure. 

However, if you test for the permissible exposure limit (PEL)—a time-weighted average used by the Occupational Safety and Health Administration (OSHA)—you would get different results. The PEL is usually measured over eight hours. For this standard, it’s not the exposure at any one moment that matters; it’s the average level of exposure over an entire workday. 

Using a source capture system, you might find a welder had a very low exposure level while working under the fume arm. However, half an hour later, that welder moved to another station but did not take the fume arm along. Unless that welder spends most of the day using that fume arm correctly, his average exposure could easily exceed the PEL standard.

Through observation, we know welders aren’t using fume arms, hoods or portable collectors properly. This means that installing a source capture system, with the extra expense involved in all of the ductwork for each source capture point, may be wasting a lot of money. 

In a perfect world, a source capture system would be the best solution for welding. In the real world, in which welders labor every day, an ambient system often is the better choice. 

An ambient system constantly changes the air inside the facility. Overall levels of fumes are lower, regardless of where you’re working. The ambient system does not require any effort or inconvenience from the welders; it works all the time without anyone doing anything. 

In some situations, you absolutely must have a hood or fume arm and it must be working correctly. For example, if the material being welded produces hexavalent chromium, there is an OSHA limit that can never be exceeded. For situations like this, the best choice may be a hybrid system with a few source capture points tied into the ambient system. 

The biggest problem with source capture systems is getting workers to use them correctly. The biggest advantage of an ambient system is that you get consistently clean air without anyone doing anything. Worker safety is always the goal. When you consider the practical problems with a source capture system, you might find that an ambient system is the best way to reach that goal. FFJ