The European Agency for Safety and Health at Work (EU-OSHA) recently highlighted isocyanates as a new and emerging risk, amid concerns that workers have not always been as well protected from these widely used substances as they should. Vicky Powell examines how workers are potentially at risk and concludes that there is encouraging evidence that the health and safety profession is making progress on controlling exposures to isocyanate hazards.

Wide application

Isocyanates are reactive chemicals which are commonly used in polyurethane plastics. The most commonly used isocyanates are toluene diisocyanate (TDI) and methylene bisphenyl isocyanate (MDI). TDI is used in the production of soft synthetic rubbers. MDI is used in producing foams, hard synthetic rubbers (elastomers), and paints or coatings.

Isocyanates were developed in Germany during World War II as part of a process to replace natural rubber, which became very scarce during the war. Nowadays, these substances are used across a surprisingly wide range of sectors, most commonly in the construction, manufacturing and motor vehicle repair industries.

They are commonly used in the production of:

  • paint products and coatings for the motor vehicle repair industries, and the paint for large commercial vehicles and structural steelwork

  • construction materials such as styrofoam, flexible foams, adhesives, elastomers and industrial floorings

  • chemical binders for bonding materials in the foundry sector

  • manufactured goods, including bedding, furniture, clothing, appliances, electronics, tyres and packaging.

The potential level of exposure in all the above settings depends greatly on the type of work processes and exact substances used. For example, MDI is used in industrial resin flooring but the low vapour pressure of the MDI used results in very little airborne isocyanate and hence carries little risk of inhalation, although there is significant potential for dermal exposure. Similarly, spray painting with isocyanate-based paints carries a greater risk to respiratory health than roller or brush painting.

Health effects

Isocyanates can affect the health of workers in a number of ways, causing:

  • irritation of the eyes, nose and throat

  • dermatitis

  • occupational asthma — this is a significant risk for workers spraying isocyanates.

Other adverse health effects linked to isocyanate exposure include cancer. In particular, various studies have noted an increased lung cancer risk among workers in the polyurethane foam manufacturing industry but the association is not altogether clear, with the researchers in a 2004 study concluding they were unable to link employment with isocyanate exposure to lung cancer risk. The Health and Safety Executive (HSE) has pointed out that there is no known case of isocyanate used in paints causing cancer.

Controlling exposures

There is encouraging evidence that the health and safety profession is beginning to more effectively control exposures to isocyanates. Certainly, it is clear that the authorities as well as leaders within the industry have identified the substances as a key area of future focus.

The EU-OSHA has noted in an expert forecast on emerging health and safety risks that the increasing use of isocyanates justifies its inclusion in a list of emerging chemical risks. The Agency pointed out that exposures to isocyanates could occur:

  • at the production stage

  • when polyurethane products containing isocyanates are used, eg when spraying

  • during processing of isocyanates, eg grinding or welding

  • when they undergo thermal or chemical degradation.

In September 2015, the HSE published research (RR1064) on the exposure of workers to isocyanates contained in vehicle spray paints in the motor vehicle repair trade, and warned workers not to lift the protective visors of their air-fed respiratory protective equipment (RPE).

The HSE says that exposure to isocyanates contained in vehicle spray paints has been the biggest cause of occupational asthma in the UK for more than a decade.

The research report pointed out that, although air-fed visors (AFVs) are used within the motor vehicle repair trade for protection against exposure to isocyanate paints, it is common practice for paint sprayers to flip up the visor immediately after spraying, while still within the paint spraying area, in order to closely examine and check the quality of the paintwork.

Often, the visor is only lifted for a few seconds but, the HSE warns, if repeated numerous times during a work shift, this could result in a 15-fold increase in exposure compared with an AFV used correctly.

Based on the research, the HSE and Health and Safety Laboratory jointly produced a new video urging painters not to lift their visors during the spraying process.

Similarly, the British Occupational Hygiene Society has drawn attention to isocyanates through its Breathe Freely campaign, which is aimed at controlling exposures to prevent occupational lung disease in the construction industry. The Chartered Society for worker health protection has produced a number of factsheets, including one for painters and another for carpenters which includes the identification of isocyanates as a hazardous substance and outlines the risks and preferred control options for each trade.

There is a hierarchy of control measures in the context of isocyanates, as follows.

  • Elimination or substitution is at the top level, eg where employers are urged to consider using less toxic substances where possible.

  • Engineering controls such as local exhaust ventilation, spray booths and the correct type of spray equipment for isocyanate-based paints.

  • Safe working methods, eg training workers not to flip visors when spray painting.

  • Personal protective equipment (PPE) at the lowest level of control, once the above is in place, where the use of gloves, overalls and suitable RPE is suggested.

Signs of progress

The HSE has recently identified the tackling of work-related ill health as one of its key themes in its new strategy to 2020. To illustrate the theme, it has published details of a four-year project to tackle occupational asthma due to exposure to isocyanates in paints within the vehicle repair industry.

The project involved representatives from across the vehicle repair industry as well as the HSE and identified new practical ways of training workers. The HSE says that simple steps such as demonstrating how to use a spray booth properly can have important results in helping to reduce exposure to dangerous chemicals among the 12,000 workers in the industry.

Similarly, the construction company Skanska has reported overall economic benefits from substituting an isocyanate-free mortar for an injectable mortar that contained isocyanate and had been a “recurrent troublesome product” for the company. The new product has offered the company a number of benefits — there is no longer any need for expensive health and safety training and PPE. Efficiency gains have also been seen since there is no longer a need to seal off areas. Finally, concerns regarding ill health of workers and environmental effects have been resolved.

In contrast, failing to control the risks associated with isocyanates can have serious consequences. In one Canadian case, staff members in a school were exposed to isocyanates during the application of roofing foam, with the result that almost half of the staff members developed asthma.

The financial and social impacts of failing to control exposures to isocyanates can be significant. However, it is encouraging to note that isocyanates are firmly on the radar of health and safety authorities and leaders, and with increasing research, guidance and awareness in this area, workers can be effectively protected.

Last reviewed 29 April 2016