Catalytic Converters

Suppliers and users of Catalytic Converters must take necessary precautions to protect workers from Refractory Ceramic Fibres.

HSE has extensive experience in the identification, characterisation, measurement and risk assessment of exposure to fibres. One potential source of hazardous fibres is the fibre mats contained within catalytic convertors (and diesel particulate filters). Catalytic converters are manufactured in many different shapes and sizes, and act to reduce volatile organic compounds (VOCs), carbon monoxide and nitrogen oxides (NO_x) emitted from vehicle exhaust gases.

In this image of a typical catalytic convertor, the fibre mat (white, outside) surrounds the metallic honeycomb structure (yellow, inside), which contains precious metals and is recyclable. These fibre mats are generally made of one of three different fibre types: Refractory Ceramic Fibres (RCF), Poly-Crystalline Wools (PCW) and Alkali Earth Wools (AEW).

RCF is classified as a Category 1B carcinogen and end-of-life catalytic converters should therefore be treated as hazardous waste. RCFs are also covered by the Registration, Evaluation, Authorisation, restriction of Chemicals regulations (REACH 2006) and Classification, Labelling and Packaging of substances (CLP 2009). This means that suppliers and users must be aware that products contain RCF when selling on or sending for recycling. Appropriate packaging and labelling must also be used to protect worker health by preventing accidental exposure to RCF during disposal and recycling.

However, neither PCW nor AEW are classified as carcinogens and, therefore, are not subject to the same regulations. PCW and AEW are visually very similar in appearance to RCF and it is therefore impossible to differentiate between them by visual inspection. Catalytic converter manufacturers and suppliers will typically replace their customers' existing stock with their own products. Without testing, large numbers of converters containing RCF could be sent for recycling (extraction of precious metals) or sold on to third parties without the appropriate precautions being taken.

The Transmission Electron Microscopy (TEM) techniques used by HSE can, however, differentiate between the fibre types, identifying which products contain RCF and which contain unregulated PCW or AEW. This protects workers by reducing the likelihood of accidental exposure to RCF during disposal and recycling. It also allows significant cost savings by identifying which converters require segregation and special treatment and which do not.

HSE is UKAS accredited (ISO 17025) for the identification of inorganic fibres by TEM/EDX. For further information, please contact Sample Registration (0203 028 3383).

More information on the science

The morphology (appearance) of the three fibre types is similar, making them difficult to differentiate. However, the techniques used at HSE's Science and Research Centre allow this to be done.

Energy Dispersive X-Ray Spectroscopy (EDX) is a technique that reveals the chemical composition of fibres. The chemical composition of AEW is sufficiently different from RCF and PCW to allow differentiation by EDX. RCF and PCW, however, are very similar and therefore require a further technique called Selected Area Electron Diffraction (SAED).

TEM image of RCF fibres

EDX spectrum from RCF fibre

The structure within PCW is largely crystalline and will therefore produce a pattern (see below) when SAED is applied, whereas the amorphous structure within RCF does not produce a pattern.

SAED pattern from PCW showing concentric ring pattern

In summary, a combination of the EDX and SAED techniques applied using HSE's TEM instrument allows the three different fibre types to be successfully differentiated.