diff --git a/app/services/hier_decomp/builder.py b/app/services/hier_decomp/builder.py
index 3718e54..416ef4d 100644
--- a/app/services/hier_decomp/builder.py
+++ b/app/services/hier_decomp/builder.py
@@ -26,7 +26,16 @@ _ATX = re.compile(r'^(#{1,6})\s+(?P<title>\S.*?)\s*#*\s*$')
 _KO_JANG = re.compile(r'^\s*(?P<title>제\s*\d+\s*장\b.*)$')
 _KO_JEOL = re.compile(r'^\s*(?P<title>제\s*\d+\s*절\b.*)$')
 _KO_JO = re.compile(r'^\s*(?P<title>제\s*\d+\s*조\b.*)$')
-_ENG = re.compile(r'^\s*(?P<title>(?:Chapter|Section|Article|Part|PART)\s+[\dIVXLA-Z]+\b.*)$')
+# _ENG: 영문 구조 헤딩(ATX 미사용 문서용). ASME 파트는 보통 ATX(`# PART PG`)로 잡혀 _ENG 의존 낮음.
+# D1: 식별자 뒤가 소문자 문장연속이면("Part III to demonstrate to the satisfaction…") 본문이므로
+# 미탐지 — 가짜 절 차단. 선택 제목은 대문자/괄호/숫자로 시작해야 헤딩 인정(소문자 시작=문장으로 봄).
+# 식별자는 번호/PG/3.31/UHX/A-1 등 (.·- 소수·하이픈 확장 허용).
+_ENG = re.compile(
+    r'^\s*(?P<title>(?:Chapter|Section|Article|Part|PART)\s+'
+    r'[\dIVXLA-Z]+(?:[.\-][\dA-Za-z]+)*'
+    r'(?:\s+[A-Z(\d][^\n]*)?'
+    r')\s*$'
+)
 
 # 코드펜스 경계 (FE outlineAnchors.ts:60 `/^\s{0,3}(```|~~~)/` 와 동일). 펜스 내부 라인은
 # heading 미탐지 — 코드블록 안 '# foo' 가 가짜 절을 만들지 않게(O3).
diff --git a/tests/hier_decomp/test_eng_matcher.py b/tests/hier_decomp/test_eng_matcher.py
new file mode 100644
index 0000000..7705bb0
--- /dev/null
+++ b/tests/hier_decomp/test_eng_matcher.py
@@ -0,0 +1,106 @@
+"""_ENG 매처 노이즈 차단 단위테스트 (asme-item-decomp-1 D1).
+
+핵심 불변식: 영문 구조 헤딩 매처(_ENG)가
+  - (음성) 본문 중간 'Part III to demonstrate…' 같은 소문자 문장연속을 가짜 절로 잡지 않고,
+  - (양성) 진짜 영문 구조 헤딩(PART PG / Part 1 / Section 3.31 / Part UHX …)은 탐지하며,
+  - (ATX 보존) _ENG 축소가 ATX 파트(`# PART PG`)·항목(`#### PG-1`)을 떨구지 않는다(ATX 우선).
+
+pytest + 단독 실행 양쪽 지원:
+  PYTHONPATH=. python3 tests/hier_decomp/test_eng_matcher.py
+"""
+from __future__ import annotations
+
+try:  # pytest 경로 (앱 패키지)
+    from app.services.hier_decomp.builder import _detect_heading, build_hier_tree
+except Exception:  # 단독 실행 (앱 deps 없이 builder.py 직접 로드 — stdlib only)
+    import importlib.util
+    import pathlib
+    import sys
+
+    _bp = pathlib.Path(__file__).resolve().parents[2] / "app/services/hier_decomp/builder.py"
+    _spec = importlib.util.spec_from_file_location("_hier_builder_t", _bp)
+    _m = importlib.util.module_from_spec(_spec)
+    sys.modules[_spec.name] = _m  # dataclass __module__ 해소
+    _spec.loader.exec_module(_m)
+    _detect_heading, build_hier_tree = _m._detect_heading, _m.build_hier_tree
+
+
+# ── 음성: 본문 문장은 헤딩 아님 (가짜 절 차단 — D1 회귀의 핵심) ──
+NEG = [
+    "Part III to demonstrate to the satisfaction of the represen-",
+    "Section V of the agreement applies to all parties",
+    "Part IV is hereby amended as follows",
+    "Article II shall be interpreted broadly",
+    "Chapter 3 describes the general method used here",
+]
+
+# ── 양성: 진짜 영문 구조 헤딩 ──
+POS = [
+    "PART PG GENERAL REQUIREMENTS FOR ALL METHODS OF CONSTRUCTION",
+    "Part 1",
+    "Part PFH",
+    "Part UHX (TUBESHEET CALCULATION)",
+    "Section 3.31",
+    "Chapter 1 Introduction",
+    "Article 5 Definitions",
+]
+
+
+def test_eng_negatives_not_detected():
+    for line in NEG:
+        assert _detect_heading(line) is None, f"가짜 절로 잡힘: {line!r}"
+
+
+def test_eng_positives_detected_as_chapter():
+    for line in POS:
+        r = _detect_heading(line)
+        assert r is not None, f"진짜 헤딩 미탐지: {line!r}"
+        _lvl, _title, nt = r
+        assert nt == "chapter", f"{line!r} node_type={nt}"
+
+
+def test_atx_part_and_item_still_detected():
+    # _ENG 축소가 진짜 ATX 파트/항목을 떨구지 않음 (ATX 우선 탐지)
+    r = _detect_heading("# PART PG GENERAL REQUIREMENTS FOR ALL METHODS OF CONSTRUCTION")
+    assert r is not None
+    lvl, title, nt = r
+    assert lvl == 1 and nt is None, r  # ATX = level(# 수), node_type None
+    assert title.startswith("PART PG")
+    r2 = _detect_heading("#### PG-1 SCOPE")
+    assert r2 is not None and r2[0] == 4 and r2[2] is None, r2
+
+
+def test_build_hier_tree_drops_false_part_section():
+    # 본문에 'Part III to demonstrate…' 가 섞여도 가짜 절이 생기지 않음
+    md = (
+        "# PART PG GENERAL REQUIREMENTS\n"
+        "#### PG-1 SCOPE\n"
+        "The rules cover power boilers.\n"
+        "Part III to demonstrate to the satisfaction of the representative\n"
+        "that the requirements are met, the manufacturer shall proceed...\n"
+        "#### PG-2 SERVICE LIMITATIONS\n"
+        "body of pg-2 here.\n"
+    )
+    titles = [n.section_title for n in build_hier_tree(md) if n.section_title]
+    assert any(t.startswith("PART PG") for t in titles), titles
+    assert any(t.startswith("PG-1") for t in titles), titles
+    assert any(t.startswith("PG-2") for t in titles), titles
+    assert not any("demonstrate" in (t or "") for t in titles), f"가짜 절 누출: {titles}"
+
+
+if __name__ == "__main__":
+    import sys
+    import traceback
+
+    fns = [(k, v) for k, v in sorted(globals().items()) if k.startswith("test_") and callable(v)]
+    failed = 0
+    for name, fn in fns:
+        try:
+            fn()
+            print(f"PASS {name}")
+        except Exception as e:
+            failed += 1
+            print(f"FAIL {name}: {e}")
+            traceback.print_exc()
+    print(f"\n{len(fns) - failed}/{len(fns)} passed")
+    sys.exit(1 if failed else 0)