On Aug. 8, ACA submitted comments to the U.S. Environmental Protection Agency (EPA) on the proposed amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Miscellaneous Coating Manufacturing (MCM) facilities. EPA’s proposed amendments would establish inorganic HAP standards for process vessels, following the mandated technology review conducted under the Clean Air Act (CAA), originally promulgated in August 2020. The current MCM NESHAP does not regulate metal HAP from process vessels.

Specifically, EPA is proposing to revise Table 1 of 40 CFR part 63 subpart HHHHH to include the emission limits that apply to process vessels based on the following findings by EPA:

  • Existing sources demonstrate initial compliance with the particulate matter (PM) emissions limit of 0.014 gr/dscf (grains per dry standard cubic foot); and
  • New sources demonstrate initial compliance with the PM emissions limit of 0.0079 gr/dscf.


During the manufacturing process, with the addition of raw materials in powder form to paint mixing vessels, emissions of metal HAP in the form of PM emissions may occur and are typically collected and routed to a PM control device (i.e., baghouse, fabric filters, cartridge filters, or scrubbers). EPA’s proposal addresses the currently unregulated metal HAP emissions from this category and proposes Maximum Achievable Control Technology (MACT) for emission sources of metal HAP.

As proposed, facilities will be required to comply continuously with the standards during all operations that emit metal HAP; but it does not apply to pigments and other solids that are in paste, slurry, or liquid form. The agency also provided a mechanism for owners and operators to demonstrate that materials containing inorganic HAP metals below certain levels are not subject to the standards, as well as a definition for “material containing metal HAP.” Finally, the agency proposed monitoring, recordkeeping, and reporting requirements that apply specifically to these facilities.

EPA has proposed a compliance date of one year from the date of a final rule for existing sources.

ACA Comments

Compliance Dates

In its comments, ACA urged EPA to provide three years to comply with the revised rule for existing facilities that need to install a PM control device or modify or replace an existing control device, since many facilities will need to do so to meet the metal HAP emission limits specified in Table 1. ACA expressed support for the one-year compliance timeline for all other existing sources.

ACA noted that the EPA proposal erroneously states that “all facilities in the source category currently have PM controls in place using existing baghouses, fabric filters, or cartridge filters.” The proposal also does not account for facilities that may need to install new controls. It is unclear whether EPA’s statement is intended to mean that each existing MCM-subject process vessel that will become subject to the metal HAP requirements is already controlled by a PM control device, or instead that each MCM-subject facility has at least one PM control device that it uses to control PM emissions from at least one of its process vessels. Because the rule applies to vessels, one or more facilities that have multiple vessels will likely need additional control devices, not all of which are necessarily in place.

Alternatives to Method 5 Compliance Testing 

When coatings are made, the addition of dry solids to MCM-subject process vessels tends to be short in

duration and often occurs infrequently, representing only a fraction of the time required to conduct Method 5 test runs. The proposed rule correctly specifies that the metal HAP emission limits apply to MCM-subject process vessels only “during the addition of dry pigments and solids that contain material containing metal HAP” (see proposal at 40 C.F.R. §§ 63.8005(a)(1)(iii) and Table 1, Item 2.c.). Moreover, facilities are required to conduct a compliance demonstration under “normal operation,” consisting of at least three Method 5 test runs of the corresponding PM control device (see proposal at 40 C.F.R. § 63.8005(i)(1)).

In practice, Method 5 test runs usually require an hour or more, whereas the addition of dry solids to an MCM-subject vessel typically occurs over a much shorter duration period. For example, under normal operation, the addition of solids from bags or sacks into some vessels occurs in no more than 10 or 15 minutes for each batch. It also might be a matter of days, or even months, before another batch is made involving the addition of dry solid metal HAP. For such vessels, only one of the three Method 5 test runs might reasonably occur while dry solids are being added to the vessel, and with that solids addition possibly spanning only part of the duration of the single-test run.

In its comments, ACA underscored that Method 5 testing is not feasible for vessels that are infrequently or rarely subject to MCM. The MCM rule applies to vessels ≥ 250 gallons only during uses of the vessel that meet the rule’s applicability criteria at 40 C.F.R. § 63.7985(a). At some facilities, only a small number of batches (in some cases, no more than one or two batches in a year) are subject to MCM, and even fewer of these might involve the addition of metal HAP in dry solids. Notably, some facilities manufacture many different types of materials in the same vessel. Some of the manufactured materials might not be coatings, and/or some materials are coatings made without “processing, using, or producing a HAP.” Neither of those uses of a vessel are subject to MCM (see 40 C.F.R. §§ 63.7985(a)(2)–(3)). Overall, Method 5 testing is not feasible for PM control devices that service one or more vessels that are subject to the MCM rule and in dry metal HAP service for a small number of instances each year.

In addition, Method 5 testing is not feasible for vessels for which PM emissions are routed to a control device that operates only while the dry materials are being added to the vessel. As such, ACA encouraged U.S. EPA to modify the proposed rule by adding design evaluations as an option in lieu of Method 5 testing with specific suggestions outlined in its comments. ACA also stressed that the agency already authorizes design evaluations under some circumstances for the MCM rule’s organic HAP emission limits and authorizes design evaluations for particulate HAP in several related NESHAP rules.

Clarification for Inapplicability of Subpart SS

Finally, ACA sought official clarification from EPA that Subpart SS, which is referenced by the existing MCM rule, does not apply to PM control devices. To avoid any potential confusion, ACA asked EPA to specify in the rule’s subsection language that Subpart SS does not apply to the proposed requirements for metal HAP by adding qualifiers and proposed explicit clarifying verbiage.

ACA will continue to engage with EPA as it progresses through its amendment rulemaking process. 

Contact ACA’s Rhett Cash for more information.