30 CFR § 57.22221 - Overcast and undercast construction (I-A, II-A, III, and V-A mines).

---
identifier: "/us/cfr/t30/s57.22221"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "30 CFR § 57.22221 - Overcast and undercast construction (I-A, II-A, III, and V-A mines)."
title_number: 30
title_name: "Mineral Resources"
section_number: "57.22221"
section_name: "Overcast and undercast construction (I-A, II-A, III, and V-A mines)."
chapter_name: "MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR"
subchapter_number: "K"
subchapter_name: "METAL AND NONMETAL MINE SAFETY AND HEALTH"
part_number: "57"
part_name: "SAFETY AND HEALTH STANDARDS—UNDERGROUND METAL AND NONMETAL MINES"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "30 U.S.C. 811."
regulatory_source: "50 FR 4082, Jan. 29, 1985, unless otherwise noted."
cfr_part: "57"
---


# 57.22221 Overcast and undercast construction (I-A, II-A, III, and V-A mines).

Overcasts and undercasts shall be—

(a) Of substantial construction;

(b)(1) Constructed of noncombustible materials; or

(2) Where constructed of combustible materials, the outside surfaces shall be coated with at least one inch of construction plaster containing perlite and gypsum; at least one inch of expanded vermiculite, Portland cement and limestone; or other coatings with equivalent fire resistance;

(c) Kept clear of obstructions.