Confusion over limits wastes time and weakens controls. UK projects should use HSE EH40 values, but you may see OSHA figures in supplier literature. Here is how to align them and act.

The HSE view (use on UK sites)

• General dust: 8‑hr TWA WEL of 10 mg/m³ (inhalable) and 4 mg/m³ (respirable).
• Respirable crystalline silica (RCS): 0.1 mg/m³ (8‑hr TWA).
• Wood dust: 3 mg/m³ (hardwood or mixed), 5 mg/m³ (softwood), inhalable fraction.

HSE expects exposure to be reduced as far as reasonably practicable, not simply kept just under the limit.

OSHA values you may encounter

• RCS PEL: 50 μg/m³ (0.05 mg/m³) 8‑hr TWA; action level 25 μg/m³.
• Total (inhalable) dust: 15 mg/m³; respirable dust: 5 mg/m³.

OSHA numbers are not a substitute for HSE limits on UK jobs. If both are cited, apply the stricter figure while meeting UK legal duties.

Practical use on site

• Build COSHH assessments around HSE EH40. If documents reference OSHA, convert units and ensure your controls satisfy HSE expectations.
• Focus on time-weighting: short high tasks can push the 8‑hr TWA over a WEL. Break tasks, rotate, or upgrade controls.
• Verify with measurement and keep records of method statements, monitor data, and maintenance of LEV/filters.

Practical takeaways

• Use HSE EH40 on UK projects; treat OSHA values as background only.
• Prioritise reduction, not box-ticking under a number.
• Time-weight exposure and control peaks with better capture and scheduling.
• Document decisions and evidence with sampling data.

Know the numbers, but control the dust. Clear, consistent use of HSE values makes planning, monitoring, and auditing far simpler.