# Relationship history for MSHA mine 1800750

Current hierarchy: **David  Humphreys → TAMKO BUILDING PRODUCTS LLC → FREDERICK GRINDING 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: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **controller_controls_mine:** Florida Rock Industries Inc → FREDERICK GRINDING PLANT; 1950-01-01 to 2007-11-15; source msha-controller-operator-history
- **operator_operates_mine:** Florida Rock Industries Cement Grou → FREDERICK GRINDING PLANT; 2000-12-01 to 2004-08-10; source msha-controller-operator-history
- **controller_controls_operator:** Florida Rock Industries Inc → Florida Rock Industries Cement Grou; 2000-12-01 to 2004-08-10; source msha-controller-operator-history
- **operator_operates_mine:** TAMKO BUILDING PRODUCTS LLC → FREDERICK GRINDING PLANT; 2004-08-11 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** David  Humphreys → FREDERICK GRINDING PLANT; 2004-08-11 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** David  Humphreys → TAMKO BUILDING PRODUCTS LLC; 2004-08-11 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Vulcan Materials Company → FREDERICK GRINDING PLANT; 2007-11-16 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Vulcan Materials Company → Florida Rock Industries Cement Grou; 2007-11-16 to 2004-08-10; source msha-controller-operator-history