How do welding emissions fit into your emissions inventory?
Keeping up with regulatory trends
Most EPA inspectors used to pay scant attention to welding fumes; these days they warrant much more attention. Regrettably the EPA relies on AP-42, a document that is thorough in some areas but not too detailed in welding processes. This means an overly zealous inspector might rate your facility as emitting more than it really does, forcing you to implement expensive and unnecessary controls
If your company makes welded tube or pipe or uses welding in its fabrication processes, you might have noticed a change over the last couple of years in how the Environmental Protection Agency (EPA) regards welding fumes. Welding processes that warranted only mild concern in the past have become sources of great concern recently. The welding processes haven’t changed; the way EPA inspectors regard them has changed.
Many permitting authorities used to regard welding fumes as either minimal or controlled if the facility had health and safety systems to protect the workers. In recent years, though, many permit reviewers have changed their tune and have begun using the EPA’s AP-42, “Compilation of Air Pollutant Emission Factors.” Although this document is the most commonly used and widely accepted tool for estimating air emissions, it’s not detailed in its coverage of welding and cutting processes. Chapter 12, Section 19, which addresses electric arc welding, has not been updated (other than a correction of a typographical error) since it was published in January 1995. This means that your local EPA inspector is likely relying on a document that, while thorough in many topics, isn’t well-suited to modern or current welding techniques.
If you do some research before an EPA inspection and if you’re prepared to present your documentation, you might prevent a zealous inspector from rating your facility as emitting more than it really does, forcing you to implement expensive and unnecessary controls. It’s a matter of reading AP-42, learning what your facility emits, compiling all the relevant information, and being prepared to defend your conclusions.
While AP-42 describes basic processes, and most are defined, some are described only in general terms and others not at all (see Figure 1). Regrettably, the only detailed welding emissions data in AP-42 concerns the first four consumable electrode welding processes listed: shielded metal arc welding (SMAW), gas metal arc welding (GMAW), flux-cored arc welding (FCAW), and submerged arc welding (SAW).
To compile an emissions inventory—a database of the air pollutants, listed by source, that your facility emits during a specific time period—you need to review AP-42 and locate your processes, using the source classification code (SCC) to find the pollutants and emission factors. Keep in mind that this isn’t limited to welding, but all of the processes that take place in your facility. The listed emission factors have a rating, A through D, which indicates the effective confidence in the factor (A indicates the highest confidence). If you think your facility’s emissions deviate slightly from the emission factors in AP-42, you’d have a better chance of making a convincing argument over a factor rated D than one rated A. That said, be prepared to present all of your research; regulators assume the ratings to be correct.
You should keep a few points about inspectors and AP-42 in mind:
- In many cases, the inspector works with potential emissions, which are the maximum emissions possible for a piece of equipment. This assumption implies that the equipment runs 100 percent of the time. This doesn’t seem realistic. For example, a process that feeds parts to a welding station at a rate that requires 45 minutes of welding every hour reduces the welding station’s actual emissions to just 75 percent of the potential emissions.
- AP-42 includes a chart of emission factors cross-referenced by electrode and pollutant (see Figure 2). Be aware that it lists emission factors as tenths of a pound per thousand pounds of electrode consumed, which could be mistaken to mean pounds per thousand pounds of electrode consumed.
- A notation of ND (no data) is usually accepted to be a zero; however, you might not want to use a zero if there is a known amount of the pollutant listed in either your electrode or base material. For example, the previously mentioned chart lists ND for the chromium content of an E410 electrode, whereas the electrode manufacturers list 12 percent chromium.
- Hazardous air pollutant (HAP) emissions may require modeling, which attempts to assess the risk to the public. The model uses ground-level, off-site concentrations of the HAP as a baseline. The modeling exercise usually allows adjustments for exhaust flow, exhaust direction, distance to nearest residence, wind direction, pollutant height at release, and other factors.
- It seems to be common practice to assume the worst. For example, where chromium is present in welding, a facility’s entire chromium emission is assumed to be hexavalent chromium, Cr(VI), a carcinogenic form of chromium, rather than the much less hazardous trivalent chromium, Cr(III). The hexavalent state is far less common than the trivalent form, and it decays with time, changing to the trivalent state.
Three Proactive Steps
If the permitting authority is allowed to make bad assumptions or mischaracterize the pollutants, your company is likely to face unnecessary emissions limitations or requirements to install controls where none are needed. Preparing a comprehensive report on your facility’s emissions is the best way to prevent the EPA inspector from dictating your calculated emissions, which often comes from a weak understanding of the process. With this in mind, you should take three actions.
- Create a complete and accurate potential-to-emit table for your facility. This table will drive the next actions that you take (if any are required).
- Determine if the calculations seem reasonable.
- Determine if permitting is required and at what level. Emissions thresholds are used to determine the level of permitting required and to characterize smaller sources of pollutants as insignificant. Insignificant sources are usually less than 5 tons per year in their potential to emit any regulated pollutant; have only generally applicable regulations; and require only a mention in any permit that is issued.
Making Your Own Potential-to-Emit Table. An accurate potential-to-emit table for a facility uses all sources of data available to calculate or characterize emissions. AP-42 is a good starting point because it is a basic reference and the data therein is accepted as accurate. The key to the electric arc welding section of AP-42 is selecting the right welding process and electrode. Emission factors vary greatly by just changing an electrode. Mischaracterizing the process can result in emission calculation errors that could have a big effect on your facility’s emissions.
After listing all of the welding processes performed in your facility, you need to match your electrode types to those listed in AP-42. Some of your electrodes will match readily; others may require some research to determine the closest match of base material. If you use some electrodes that don’t have a close or approximate match, you’ll have to determine the emissions by other means, such as:
- Asking your welding materials supplier.
- Researching the information using engineering reference manuals (request from the electrode manufacturer).
- Using an emission inventory from a similar source that has emission factors approved by your permitting authority (be sure to match all three factors: process, electrode, and base material).
- Source testing.
Source testing, the most costly process, is a last resort. It requires a way to collect all the emissions from the process, quantify them, and determine the chemical components.
Bear in mind that OSHA records and testing can be a useful source of site-specific data.
Do Emissions as Calculated Seem Reasonable? After completing an emissions potential for your facility, you can then attempt to determine if they seem reasonable. For example, 100 tons per year is not reasonable. This quantity would make the facility visible for miles. Even 25 tons per year is probably a result of a miscalculation; without process controls or building ventilation, this much particulate would fill the room with smoke, making the work environment extremely uncomfortable.
Are the chemical emissions that you have calculated reasonable? If you have calculated emissions for chromium, lead, or nickel, are those metals present in the process? If you are using an electrode, flux, and base material that are certified lead-free, there is no reasonable expectation that they will emit lead emissions because none is present in the process materials.
Determine If Permitting Is Required. Having completed an emissions potential for the facility, you can then determine if permitting is required. Permitting requirements vary from authority to authority and may have very low emissions levels for a nonattainmentarea when compared to the relatively high emissions potential needed to trigger permitting in an attainment area. Of course, this is a simplification of permitting requirements because potential to emit is only one component of the permitting requirements determination.
If you determine that permitting is required, or if you are completing an emission inventory for a reapplication, your next step is to ensure your application is complete. Include a detailed description of the processes, the materials you are processing, and relevant data regarding emission rates. If you use site-specific data from testing or process-specific data from material safety data sheets (MSDS) or supplier certifications, include this information.
To Apply or Not to Apply
In the end, you might decide that you don’t need to apply for a permit. If this is the case, it’s still necessary to maintain all the documentation on-site so you can defend your decision. Good data on the front end helps prevent misunderstandings and data generation later, under time constraints, if your decision is questioned by a permitting authority.
Because you can’t control the actions of the permitting authority, your efforts should focus on the areas you can control—the permit you apply for, the records you keep, the way you maintain your process and emissions controls, what you report, and when you report it.
What Is An Emissions Inventory?
The Environmental Protection Agency defines an emissions inventory as a database that lists, by source, the amount of air pollutants discharged into the atmosphere during a given time period. It specifically identifies the area of interest as a community, but the concept also applies to every contributor in the community. As a manufacturer that uses welding processes, it’s incumbent on you to develop an emissions inventory.
The development of a complete emission inventory is an important step in an air quality management process. Emission inventories are used to help determine significant sources of air pollutants, establish emission trends over time, target regulatory actions, and estimate air quality through computer dispersion modeling. An emission inventory includes estimates of the emissions from various pollution sources in a specific geographical area. A complete inventory typically contains all regulated pollutants.
In the U.S., the EPA Clearinghouse for Inventories & Emission Factors contains information on emissions inventories, emissions factors, software and tools used for emissions inventories, and emissions modeling. For an overview of the mobile source category and specific methods to identify and inventory sources; estimate emissions; and establish and maintain a useful, current mobile source emissions inventory, you may access “Procedures for Emission Inventory Preparation, Chapter IV: Mobile Sources” that was prepared by the U.S. Department of Transportation and U.S. EPA. For information on the “Compilation of Air Pollutant Emission Factors,” you may access EPA’s AP-42 documentation.”
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