Quick answer: Carbon fibre dust is not respirable crystalline silica (RCS) — the RCS WEL of 0.1 mg/m³ does not apply. However, CFRP machining generates fine respirable fibre fragments classified as potentially carcinogenic (IARC Group 2B) and the correct COSHH assessment applies the general inhalable dust WEL (10 mg/m³) and respirable dust WEL (4 mg/m³). H-Class extraction (H14 HEPA, 99.995%) is the correct and defensible standard for all CFRP machining environments — M-Class is not adequate for fine fibrous particulate with this hazard profile.
Carbon fibre dust and silica dust are not the same hazard. But they share enough of the same hazard profile — fine inhalable particles, deep lung penetration, long-term irreversible damage — that contractors and EHS managers who understand silica risk often ask the same question about CFRP: do the same rules apply? The answer is nuanced, and getting the nuance wrong in either direction creates problems.
This article explains what carbon fibre dust actually is, how it differs from RCS, what COSHH 2002 requires for it, and why H-Class extraction is the correct standard for carbon fibre composite machining environments regardless of the RCS framing.
CFRP machining generates three distinct dust fractions: respirable carbon fibre fragments (the primary inhalation hazard), resin dust and volatiles (a separate COSHH hazard at elevated temperatures), and mixed fine particulate. What CFRP dust is not is respirable crystalline silica. A COSHH assessment that applies the RCS WEL to CFRP machining operations is technically incorrect — even if the practical outcome (H-Class extraction) happens to be the same.
Under COSHH Regulations 2002, the relevant WEL for carbon fibre dust is the general inhalable dust WEL of 10 mg/m³ and the respirable dust WEL of 4 mg/m³ — carbon fibre has no dedicated WEL. The long-fibre fraction is classified as possibly carcinogenic (IARC Group 2B) and the resin fraction introduces additional hazards. Industry practice in motorsport and aerospace applies controls equivalent to those used for hazardous fine particulate. The extraction class that meets this requirement in CFRP machining environments is H-Class. M-Class at 99.9% allows the finest fibre fraction to pass through the filter and re-enter the breathing zone. H-Class at 99.995% with sealed disposal contains the captured material through the filter change.
In Motorsport Valley F1 and aerospace composite facilities, CFRP machining is carried out under controlled conditions. CNC machining requires LEV at the machine. Hand trimming, drilling and edge finishing — the operations most likely to be carried out in less controlled conditions — generate the highest operator exposure and require the most careful control. The COSHH assessment should specify the dust fraction, the WEL applied (inhalable and respirable, not RCS), the engineering controls, the extraction class and filtration standard (H-Class, ULPA15, sealed Type H disposal), RPE specification (FFP3 minimum for manual operations), and disposal method for captured CFRP dust.
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