Quick answer: Bath stone (oolitic limestone) is the dominant building material across Bath as a whole — not just listed structures. It contains a free crystalline silica fraction that generates RCS during power tool operations, making H-Class extraction (H14 HEPA, 99.995%) the legal minimum under COSHH 2002 for cutting, grinding and core drilling on this material. The soft, friable nature of Bath stone means fine dust is generated rapidly — extraction must be operational before the cut starts. This applies city-wide across the UNESCO World Heritage Site boundary, not only to heritage specialists.
Bath is unusual among UK cities in one specific and practically important way: the primary building material is not brick or concrete or a mixture of different stone types. It is overwhelmingly one stone — Bath stone, the warm golden oolitic limestone quarried from the Box and Corsham seams of the Jurassic limestone belt. Any contractor carrying out masonry work in Bath is almost certainly working Bath stone regardless of where in the city the project is located. The H-Class extraction requirement is therefore not a consideration for heritage specialists on listed structures. It is the baseline for masonry work across the city as a whole.
Bath stone's softness means that cutting and grinding generates high volumes of fine particulate rapidly. Its free silica content is lower than some other limestone types, but still sufficient to generate RCS above the COSHH WEL during power tool operations. The city-wide extent of Bath stone use means that H-Class applies to maintenance and repair work on Georgian townhouses, commercial premises in the city centre, and any construction project involving existing building fabric throughout the UNESCO World Heritage Site boundary — which covers the majority of the historic city. COSHH 2002, CDM 2015, and World Heritage Site planning requirements all converge on the same practical outcome: H-Class extraction, specific to Bath stone, across all masonry work in the city. For contractors working in Bath, the practical starting point is to assume H-Class extraction is required for any masonry work generating Bath stone dust until the COSHH assessment for the specific task demonstrates otherwise.
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