Choosing an emission limit under MACT

Susan Bassett is a chemical engineer and air quality consultant. As president of Cogent Regulatory Science Inc. (Centennial, Colo., U.S.A.), she helps composite parts manufacturers understand and comply with air quality regulations. The time has come for composite parts manufacturers to consider compliance

The time has come for composite parts manufacturers to consider compliance strategies in response to the Reinforced Plastic Composites Products MACT (Maximum Achievable Control Technology) regulations recently codified in 40 Code of Federal Regulations (CFR) Part 63, Subpart WWWW. The regulations grant many manufacturers a range of compliance options in terms of materials and emission control techniques, but one of the most interesting facets of the new MACT rule is that many can also choose their emission limit.

Choice of emission limit is not available to everyone. Very large existing sources - those operating centrifugal casting or continuous lamination/casting production lines and emitting 100 tons per year or more of hazardous air pollutants (HAPs) from these operations - have no option but to reduce emissions by at least 95 percent. ("Existing sources" commenced construction of their composites manufacturing facilities on or before August 2, 2001.) But most other existing sources, especially among open molders, have a variety of compliance options, including several different maximum emission limits, depending on the type of resin, application equipment, and emission control method being used. The following considers emission limit options available to open molders who are classified as existing sources but do not trigger the 95-percent emission reduction requirement.

Consider an open molding operation (excluding centrifugal casting) using non-corrosion-resistant, non-high-strength production resin ("non-CR/HS" as denoted in Subpart WWWW). Although this is just one subset of composites manufacturing, the number of compliance options and their implications are mind-boggling. Confusion stems from the confluence of emission factors, emission limits, maximum HAP content for "compliant" resins, and multiple tables included at the end of the regulations. Plus, there are 34 different equations to choose from if your compliance strategy requires you to calculate emissions. Which numbers do you comply with?

Table 3 to Subpart WWWW lists basic emission limits (for comparison's sake, the table accompanying this article presents a portion of Table 3 and Table 7). Both mechanical and manual resin application have emission limits of 87 lb organic HAP per ton of resin. Mechanical application includes use of spray guns (an atomized mechanical method), and pressure-fed rollers and flow coaters (non-atomized mechanical methods). Manual application includes use of brushes and non-resin-feed rollers. In contrast, the emission limit for filament winding is much higher at 188 lb organic HAP per ton of resin.

Table 3, as created by the U.S. Environmental Protection Agency (EPA), also contains a column listing "the highest organic HAP content for a compliant resin." In the accompanying table, this column is labeled "Maximum organic HAP content." Both descriptions are misleading because the listed maximum HAP limits are too low in some cases. The published HAP content maximums assume that the resin is not vapor suppressed and that neither vacuum bagging nor closed mold curing with roll-out are used. For example, if you use a vapor-suppressed resin for nonatomized mechanical resin application, your allowable organic HAP content would be more than 38.4 percent because the applicable emission factor equation in Subpart WWWW's Table 1 takes vapor suppression into account. Before accepting the Table 3 maximum organic HAP content limits as the limits for your operations, double check maximum content limits by calculating emission factors using appropriate equations from Table 1.

Table 3 gives the maximum HAP content limit for nonatomized resin application, but does not include a limit for atomized application. Assuming no vapor suppression or other emission-reduction activities, the upper limit for atomized application would be about 25.7 percent. For filament winding, the maximum HAP content is 45.0 percent (again, assuming no vapor suppression).

The relationship between Subpart WWWW's Table 1 and Table 3 is unclear to many people. Table 1 contains equations for calculating emission factors. After calculating an emission factor (with units of lb organic HAP per ton of resin), you compare the emission factor to the appropriate emission limit in Table 3. An individual resin is compliant if the calculated emission factor (based on the type of resin application and other factors) does not exceed the Table 3 emission limit. An individual resin is also compliant if its organic HAP content does not exceed the applicable maximum listed in Table 3 (in this case, emission factor calculation is not required).

Some resins may exceed Table 3 emission limits if the facility averages multiple resins or operations together and demonstrates that 12-month rolling averages comply with applicable Table 3 limits. The averaging calculation depends on the type of averaging being used by the facility. Equations and instructions are in §63.5810(a-b).

There is, however, a perfectly legal way to exceed Table 3 emission limits on a much larger scale - the "same-resin" approach described in §63.5810(c). Under this compliance approach, a facility can meet the organic HAP emission limit for one operation type (e.g., filament winding, nonatomized mechanical application, etc.) and use the same resin(s) for all operations of that resin type. In this case, the resin type is non-CR/HS. A quick look at the "Table 7" columns reproduced here shows that high-HAP resins can be used for a variety of manufacturing operations.

For example, if a facility operates a filament winder using a 44-percent HAP resin, the 44-percent resin also may be used for that facility's mechanical and nonmechanical operations. Nonatomized and atomized mechanical application with the 44-percent resin is allowed, representing huge allowable emission increases over Table 3 limits. Similar analysis works for facilities with at least one nonatomized, mechanical resin application. If a manufacturer has at least one pressure-fed roller or flowcoater, and uses it to apply a resin with, say, 38 percent HAP content, the same resin may be used in all spray guns, as well, despite the fact that Table 1 calculations limit resins used for atomized applications to 25.7 percent HAP content (assuming no emission control).

What if your facility would like to use higher-HAP resins, but not the exact same resin as is used in filament winding or nonatomized mechanical application? That works, too! In fact, in this case, there is even greater flexibility. A provision in §63.5810(c)(3) allows facilities to average the HAP content of multiple resins (within the same resin type) and compare the average to applicable Table 7 limits.

EPA originally justified the same-resin approach because using multiple resins to manufacture a single product could cause problems. However, in the published MACT rule, neither the regulatory text nor the preamble restricts this same-resin approach to resins used to make a single product.

Should your facility pursue a high-HAP compliance strategy based on the same-resin and Table 7 options? The decision is yours. But, before mapping out your compliance strategy, make sure you understand all of the compliance options available to you. And be aware that the EPA plans to address these issues, either by issuing guidance or by revising the regulations. EPA's Keith Barnett, author of Subpart WWWW, will make a MACT presentation at COMPOSITES 2003 (Anaheim, Calif., U.S.A., Oct. 1-3) and will gather input from fabricators on additional issues that require clarification.