Contaminant Clouds Part 5 – Plastic Fume

Contaminant Clouds Part 5 – Plastic Fume

Thermal degradation of plastics can produce a wide range of airborne contaminants. Many industrial settings may generate plastic fume e.g. plastic injection moulding (PIM), plastic extrusion, and other plastic manufacturing processes. What’s in the fume? How hazardous is this? We can start by looking at the safety data sheet (SDS) for the plastic materials being processed. As well as the SDSs of other materials in use such as fillers, stabilisers, fire retardants or pigments. However, the SDS may not provide sufficient information on the thermal degradation products. This may tell you the composition of the material in its normal state. But under section 10 of the SDS where this lists thermal decomposition products, this may generically state ‘Formation of toxic gases is possible’. Which isn’t very helpful. Where do we go from here then? What compounds should we include in your sample analysis when assessing personal exposure to the fume (if personal exposure monitoring has been deemed necessary in that situation under COSHH regulation 10)?

Guidance is available from the HSE. See HSE document RR797 titled ”Investigation of potential exposure to carcinogens and respiratory sensitisers during thermal processing of plastics’’ (insert hyperlink This shows results of a laboratory study on major thermal breakdown products of some common thermoplastics such as Polyvinylchloride, Polypropylene, Low density polyethylene, Polystyrene, Polyacrylonitrile-butadiene styrene and Polymethyl methacrylate. The research report also discusses the potential for exposure to carcinogens in the thermoplastic processing and finishing industries. This particular study found that the levels of carcinogens detected in the process fume at the sites investigated were either low or not detectable. Carcinogens detected included benzene, formaldehyde, naphthalene and other carcinogenic polycyclic aromatic hydrocarbons. Low levels of respiratory irritants were also found such as aldehydes, ketones and hydrochloric acid. This is to name only a few of the potential hazardous substances present. Depending on the situation and materials in use, the contaminant cloud could also potentially contain the following examples: methyl methacrylate, toluene, styrene, methanol, butane, cyclohexanone.

Although levels of airborne hazardous substances were low in the sites visited for this research report (HSE’s RR797), these processes may have had exposure controls in place. Therefore it shouldn’t be assumed that all thermoplastic processing and finishing industries will also show plastic fume exposure at low levels. How do we control exposure to plastic thermal degradation fume to ensure exposure is kept to a low level? As always, we work from the top of the hierarchy of control downwards. Specific examples of process modification and engineering controls can include process temperature control and forced mechanical dilution ventilation. Local exhaust ventilation (LEV) and respiratory protective equipment (RPE) may also be needed but this depends on the control needs as determined via the process-specific risk assessment.

Another excellent source of guidance is the HSE’s document PPIS13 ”Controlling fume during plastics processing” (hyperlink here This also lists potential hazardous substances found in the thermal degradation of various plastic materials, (styrene, acrolein, hydrogen chloride, butadiene, phenol, formaldehyde, etc) when they were heated above their recommended upper process temperature. The document takes us through the health hazards including respiratory sensitisers, irritants and carcinogens. Acute effects may include severe irritation but the the effects can be long-term and irreversible depending on the situation.

Our understanding of the fume composition is important; different plastics, different additives, different process temperatures creates a different contaminant cloud composition and at varying extents to which the cloud is generated. Once understood, we need to control this exposure proportionately to the risk level. The HSE document PPIS13 also covers how to influence fume production e.g. controlling material processing temperature ranges and residence/ dwell times. This document gives specific advice on operational controls, temperature control, cleaning procedures, machine/screw maintenance, ventilation and how to maintain these controls. EEUK Group’s occupational hygiene consultants can help the employer assess the level of exposure and give guidance on how to select suitable controls.