BifrostRAG: Bridging Dual Knowledge Graphs for Multi-Hop Question Answering in Construction Safety

Abstract: Information retrieval and question answering from safety regulations are essential for automated construction compliance checking but are hindered by the linguistic and structural complexity of regulatory text. Many compliance-related queries are multi-hop, requiring synthesis of information across interlinked clauses. This poses a challenge for traditional retrieval-augmented generation (RAG) systems. To overcome this, we introduce BifrostRAG: a dual-graph RAG-integrated system that explicitly models both linguistic relationships (via an Entity Network Graph) and document structure (via a Document Navigator Graph). This architecture powers a hybrid retrieval mechanism that combines graph traversal with vector-based semantic search, enabling LLMs to reason over both the meaning and the structure of the text. Evaluation on a multi-hop question dataset shows that BifrostRAG achieves 92.8 percent precision, 85.5 percent recall, and an F1 score of 87.3 percent. These results significantly outperform vector-only and graph-only RAG baselines that represent current leading approaches. Error analysis further highlights the comparative advantages of our hybrid method over single-modality RAGs. These findings establish BifrostRAG as a robust knowledge engine for LLM-driven compliance checking. Its dual-graph, hybrid retrieval mechanism offers a transferable blueprint for navigating complex technical documents across knowledge-intensive engineering domains.