# Relationship history for MSHA mine 2301487

Current hierarchy: **Didier-Werke Ag → North American Refractories Company → Farber Refractories Plant**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **operator_operates_mine:** North American Refractories Company Inc → Farber Refractories Plant; 1950-01-01 to 1985-12-31; source msha-controller-operator-history
- **controller_controls_mine:** Allied-Signal Inc → Farber Refractories Plant; 1950-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Allied-Signal Inc → North American Refractories Company Inc; 1950-01-01 to 1985-12-31; source msha-controller-operator-history
- **operator_operates_mine:** North American Refractories Company → Farber Refractories Plant; 1986-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Didier-Werke Ag → Farber Refractories Plant; 1986-01-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Didier-Werke Ag → North American Refractories Company; 1986-01-01 to current/open; source msha-controller-operator-history