---
kind: "section"
citation: "40 C.F.R. § 63.747"
title: "40"
number: "63.747"
heading: "Standards: Chemical milling maskant application operations."
url: "https://uscodex.org/cfr/40/63.747"
---

# §63.747. Standards: Chemical milling maskant application operations.

- (a) Each owner or operator of a new or existing chemical milling maskant operation subject to this subpart shall comply with the requirements specified in [paragraph (c)](#c) of this section for those chemical milling maskants that are uncontrolled (no control device is used to reduce organic HAP emissions from the operation) and in [paragraph (d)](#d) of this section for those chemical milling maskants that are controlled (organic HAP emissions from the operation are reduced by the use of a control device).
- (b) Each owner or operator shall conduct the handling and transfer of chemical milling maskants to or from containers, tanks, vats, vessels, and piping systems in such a manner that minimizes spills.
- (c) **Uncontrolled maskants—organic HAP and VOC content levels.** Each owner or operator shall comply with the organic HAP and VOC content limits specified in paragraphs [(c)(1)](#c-1) and [(c)(2)](#c-2) of this section for each chemical milling maskant that is uncontrolled.
  - (1) Organic HAP emissions from chemical milling maskants shall be limited to organic HAP content levels of no more than 622 grams of organic HAP per liter (5.2 lb/gal) of Type I chemical milling maskant (less water) as applied, and no more than 160 grams of organic HAP per liter (1.3 lb/gal) of Type II chemical milling maskant (less water) as applied.
  - (2) VOC emissions from chemical milling maskants shall be limited to VOC content levels of no more than 622 grams of VOC per liter (5.2 lb/gal) of Type I chemical milling maskant (less water and exempt solvents) as applied, and no more than 160 grams of VOC per liter (1.3 lb/gal) of Type II chemical milling maskant (less water and exempt solvents) as applied.
  - (3) **The requirements of paragraphs (c)(1) and (c)(2) of this section do not apply to the following—**
    - (i) Touch-up of scratched surfaces or damaged maskant; and
    - (ii) **Touch-up of trimmed edges.**
- (d) **Controlled maskants—control system requirements.** Each control system shall reduce the operation's organic HAP and VOC emissions to the atmosphere by 81% or greater, taking into account capture and destruction or removal efficiencies, as determined using the procedures in [§ 63.750(g)](/cfr/40/63.750.md?p=g) when a carbon adsorber is used and in [§ 63.750(h)](/cfr/40/63.750.md?p=h) when a control device other than a carbon adsorber is used.
- (e) **Compliance methods.** Compliance with the organic HAP and VOC content limits specified in paragraphs [(c)(1)](#c-1) and [(c)(2)](#c-2) of this section may be accomplished by using the methods specified in paragraphs [(e)(1)](#e-1) and [(e)(2)](#e-2) of this section either by themselves or in conjunction with one another.
  - (1) Use chemical milling maskants with HAP and VOC content levels equal to or less than the limits specified in paragraphs [(c)(1)](#c-1) and [(c)(2)](#c-2) of this section.
  - (2) Use the averaging provisions described in [§ 63.743(d)](/cfr/40/63.743.md?p=d).

## Notes

### Amendments

[60 FR 45956, Sept. 1, 1996, as amended at 63 FR 15021, Mar. 27, 1998]

### Source

Source: 60 FR 45956, Sept. 1, 1996, unless otherwise noted.

### Authority

Authority: 42 U.S.C. 7401 et seq.

### Source

Source: 57 FR 61992, Dec. 29, 1992, unless otherwise noted.

### Amendments

[60 FR 45956, Sept. 1, 1996, as amended at 63 FR 15021, Mar. 27, 1998]