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Isocyanate Compounds – A Guide on Exposure, Hazards, and Precautions  

08/11/2022by minal.metkari0Read: 8 minutes
Isocyanate Compounds – A Guide on Exposure, Hazards, and Precautions  

Isocyanate compounds are harmful chemicals used in various manufacturing materials like plastics, paints, polyurethane foams, rubbers, adhesives, and varnishes.

Isocyanates are available in a variety of forms. A paint hardener labelled to be free of isocyanates—that is, no isocyanate monomers2—could still be toxic due to a high proportion of other isocyanate forms, including polymeric isocyanates. The thermal decomposition of polyurethane materials, including coated metals, can also produce isocyanates. Isocyanates should not be mistaken for cyanates, isocyanides, or cyanides, all of which have distinct properties and health consequences.

Workplaces with Isocyanate compounds are harmful to the workers’ health as they can be affected by short and long-term health problems.

Workplace activities that can lead to Isocyanate Exposure

Below are some of the workplace activities that can lead an Isocyanate exposure among workers:

1. Spraying activity

Various spraying activities, like spraying of adhesives and lacquers and spray painting, etc., contain isocyanate compounds, which can be inhaled by the workers performing it. Their skin can also be affected by it. Workers working in industries where a two-pack mix of isocyanate substances is sprayed are at a major risk of isocyanate exposure.

The various jobs, like vehicle repair, cabinet and furniture making, spa manufacturing, spray painting, etc., amount to exposure to isocyanate compounds.

Isocyanates used in paints, such as HDI, are usually present as pre-polymers and polymeric isocyanates. When sprayed, pre-polymers and polymeric isocyanates cause the same health effects as that caused by free isocyanates as a result of aerosols and overspray, which can be inhaled.

2. Manufacturing operations

Synthetic rubbers, Polyurethane foams, foaming operations, production of plastics, insulation making, cores for foundry casting, and furniture making process, and lead to the gas formation or a blowing agent. This can improve the release of isocyanate vapour or aerosols. Heating isocyanates before mixing with resins. This can increase the volatility of isocyanates. Inhaling isocyanates during storage of product while they are still curing. There may be unreacted isocyanates which can evaporate, creating an unsafe atmosphere. Hot wire-cutting of polyurethane foams. In this situation, isocyanate vapours can be released. High-temperature bonding involving polyurethane-based sealers.

3. General transportation and storage

Isocyanate exposure is common where improper transportation or storage or transportation, where water spillage is frequent, and no control precautions have been taken to reduce or eliminate the possibility of exposure.

Newly manufactured polyurethane products release isocyanate fumes when stored at the time of their curing.

4. Welding of pipework

The deaccelerating of the hot welding of pipework by polyurethane foams can cause their degradation and lead to the emission of isocyanate compounds.

5. Varnishes

Some of the partially cured varnishes might comprise isocyanate compounds that may be emitted until the varnishes are completely cured.

Furthermore, the removal of varnishes, when hot, might release isocyanate compounds too.

It is, therefore, essential to curate the varnishes before storing them, and they should not be removed when they are hot.

6. Mining

Filling tyres with a two-pack mix of polyurethane foam (flat proofing), spraying ground and strata surfaces and injecting voids to make them stable for mining operations.

Mixing a two-pack mix material in tyre fitting workshops and injecting it into tyre voids. Isocyanates are released from tyres filled with polyurethane foam if the tyres are damaged or catch fire during use or maintenance. Transferring isocyanates and polyol by hose over distances underground and mixing isocyanates and polyol in underground restricted spaces and ventilated areas. Polyurethane resins are being sprayed or injected by workers. This can also affect others nearby.

Polyurethane used in ground or strata control for coal mines may act as an insulator and increase the risk of spontaneous combustion. Polyurethane should not be used where coal is prone to spontaneous combustion. Polyurethane and toxic gases are released, e.g., hydrogen cyanide (HCN). This can promote the spread of fires. Welding sparks ignite polyurethane foam and create a fire underground.

Health Hazards Caused by Isocyanate Compounds

Exposure to isocyanate compounds can cause severe health issues for workers exposed to it. Employees who are constantly exposed to these harmful chemicals can suffer from respiratory tract disorders affecting the mouth, nose, lungs, and throat.

Here are the health hazards caused by the inhalation of isocyanate compounds among factory workers:

1. Inhaling disorders

  • Difficulty in breathing
  • Coughing and wheezing
  • Tightness of the chest
  • Shortness of breath
  • Asthma-like symptoms
  • Headache and discomfort
  • Irritation in the respiratory tract

2. Skin and Eye Irritation

Isocyanates cause irritation to the skin and eyes. Contact with isocyanates with the skin or the eyes can cause skin irritation, swelling, blistering, and reddening. Long-term skin exposure to isocyanates can result in chronic skin conditions such as dermatitis.

Chemical conjunctivitis can be caused by eye splashes.

3. Sensitisation

Many isocyanates have the potential to cause respiratory sensitisation, and some have the ability to cause trigger allergic dermatitis. This may not be limited to the point of contact, affecting the surrounding skin as well. Skin exposure is thought to cause respiratory problems.

Sensitisation results from high exposure to isocyanate compounds, while the latter’s low exposure can decline the functioning of the lungs.

Workers become sensitised to isocyanates commonly after their initial exposure. This time period differs significantly and can range from a few weeks to two years or above.

Workers become sensitised to isocyanates commonly after their initial exposure. This time period differs significantly and can range from a few weeks to two years or above (10 years and more in some cases).

A sensitised person will further face inhalation disorders described above if the exposure is continued further.

As of now, identifying individuals susceptible to respiratory sensitisation is not possible due to the unavailability of the screening test. Hence, a sensitised person should be prevented from working in environments that can cause further isocyanate exposure.

4. Carcinogenicity

Exposure to carcinogens should be eliminated or minimised as low as reasonably practicable.

The isocyanates given below are classifiable as per the GHS as Carcinogenicity Category 2, which is

suspected of causing cancer4:

  • 4,4’-methylene diphenyl diisocyanate.
  • 2,2’-methylene diphenyl diisocyanate.
  • o-(p-iso-cyanato benzyl) phenyl isocyanate

Risk Assessment of Isocyanate Compounds

Isocyanate compounds should be assessed before being used for work purposes.

The risk assessment process should include analysing of risks associated with the storage, use, handling, or removal of isocyanates in the workplace of an organisation. The focus should be on the way they are generated or used, as well as the possible ways in which it can come in contact with the workers. The above involves analysing potentially hazardous isocyanate reactions with other substances as well as those reactions which could produce isocyanates. Isocyanates are commonly inhaled in the workplace through mists, vapours, dust, or aerosols. Isocyanates and toxic metabolites can also enter in the body through the eyes or the skin.

The exposure risk is determined by the compound’s volatility, the application process, and the frequency and duration of the exposure.

Isocyanates with a lower molecular weight are the most volatile. Partially polymerised isocyanate compounds, as well as their aerosols, possess the same health issues.

Compliance with Exposure Standards

In an organisation, workers handling isocyanates must not be exposed to its atmospheric concentrations, which are greater than the workplace exposure standard provided for isocyanates.

The standards for isocyanates, all* are as follows:

TWA** 0.02 mg/m3

STEL*** 0.07 mg/m3

Sensitiser Notices

Where –

*- The isocyanate fraction of the compound is measured.

**- Time-weighted average measurement is taken over 8 hours.

***- Short-term exposure limit—time-weighted average measurement taken over 15 minutes.

Air Monitoring

Air monitoring may also be necessary to ensure exposure limits do not exceed workplace exposure standards. Direct reading instruments and detection badges, as well as more complex methods for aerosols of higher molecular weight monomers and pre-polymers, can be used to calculate isocyanate concentrations in the atmosphere.

Corrective action needs to be undertaken when the exposure standards are exceeded, as detected by the air monitoring process.

To ensure that you correctly apply the corrective measures, you can seek professional help from Occupational Hygienists in Melbourne, Sydney and Brisbane from Anitech.

You can call us on 1300 802 163 or email us at info@anitechgroup.com

How to control occupational hygiene risks associated with Isocyanates

Anitech’s Occupational hygienists in Melbourne, Sydney and Brisbane recommend that organisations follow the Hierarchy of controls

WHS regulations require that a company or undertaking do everything reasonably possible to eliminate or reduce risks.

Methods of risk control are ranked from most secure and reliable to least secure and reliable. This is known as the control hierarchy. You must work your way through the same hierarchical system to manage risks effectively.

To start with, organisations should check if the hazards can be completely eradicated from their workplace. If it is not practically possible to completely eliminate the risk, consider one or more of the following options in the order they appear below to minimise risks as far as is reasonably practicable:

  • Substitute the risk with a safer option.
  • Isolate the hazard from people.
  • Use engineering controls.

If post implementation of the above-given control measures, a risk still persists, organisations should consider the below given controls exactly in the order given to reduce the remaining risk as far as it is possible.

  • Use administrative controls.
  • Use personal protective equipment (PPE).

If a single control is not sufficient to reduce the risks, Companies can use a combination of both. You need to consider all possible control measures and take a decision about the ones that suit your workplace.

The factors to be taken into consideration while selecting controls include the suitability and the availability of control measures, with a choice for using substitution, engineering controls, or isolation to reduce risks prior to using PPE or administrative controls.

Cost may also play a key role, but you can only consider this after all other factors have been taken into account.

Substitutes

Isocyanates should be replaced by a less dangerous substitute or a less harmful procedure.

Single-spray paints shall be used instead of double-spray paints.

Companies can use polyurethane products comprising a fire retardant

Administrative Controls

Workplace areas where isocyanates are used should be restricted to only people trained and authorised to handle it.

The time limit for which workers are handling isocyanate-containing or generating jobs should be limited. They must also be informed about any health monitoring needs. Workers should be given proper training on the safe handling of jobs that involve exposure to isocyanate compounds.

Notices and caution boards shall be placed in areas where isocyanate compounds are used.

Engineered or Automated Controls

Organisations should automate process operations and those involving the handling of isocyanates, such as transferring and drying.

They should use enclosures with ventilation systems like fume cupboards, spray, and downflow booths.

Isolation from Incompatible Substances

It is essential to isolate isocyanate from substances it is not compatible with to prevent an accident or chemical reactions.

Acids, alcohols, water, amines, and oxidising agents are not compatible with isocyanates.

Embedding or automating processes using HDI or TDI or HDI, and work procedures where either the isocyanates are sprayed or heated above 60° C. Furthermore, it is essential to separate other workers who are not involved in isocyanate work to limit their exposure to isocyanates.

Protective Equipment

Companies must provide personal protective equipment to each worker who handles jobs involving isocyanate compounds.

The various protective gears include – chemical-resistant gloves, supplied-air respirator, aprons, eye protection, and an overall suit or kit to secure personal contact with a dangerous chemical.

Ventilation systems

Care in the selection, design, installation, operation, and training in the use of ventilation

systems is essential to ensure these systems minimise airborne concentrations of isocyanates

in the workplace. Common ventilation systems for controlling exposure to isocyanates are

outlined below.

Spray booths

Spray booths help in providing workers with an efficient method to control their exposure to isocyanate compounds while performing spraying tasks. These must be designed and maintained as per AS/NZS 4114.1: Spray painting booths, designated spray painting areas and paint mixing rooms – Design, construction, and testing, and AS/NZS 4114.2: Spray painting booths, designated spray painting areas and paint mixing rooms – Installation and maintenance.

Since spray booths may not adequately protect the operator during spraying, respiratory protection can also be required. They do, however, provide good containment, removal of vapour and mist after spraying, and protection for other workers.

Local Exhaust Ventilation

Isocyanate vapours and mists are captured as nearer to the significant source of release as possible using local exhaust ventilation systems. To filter isocyanates, local exhaust ventilation should be equipped with a particulate filtration system. On exhaust outlets, high-efficiency filters should be used.

If the total enclosure of the method is not feasible, local exhaust ventilation is required where TDI or HDI is used or where isocyanate or polyurethane is sprayed. Local exhaust ventilation should have airflow specifications, as well as the airflow should be checked on a regular basis.

Dilution Ventilation Systems

Dilution ventilation systems dilute and replace contaminated air with fresh air, which is supplied to the workplace by either the natural air or with the help of mechanical exhaust fans. This system can be used in conjunction with local exhaust ventilation.

While dilution ventilation alone will not suffice in Companies where isocyanates are often used, it might be adequate in storage areas.

Australian businesses must get their ventilation systems designed by experts.

Companies should always keep ventilation inlets and outlets clear, and air coming from extraction exhausts should not be pumped back or released near air vents or compressors providing breathing air.

Furthermore, Ventilation systems require regular planned preventative maintenance.

For more information on the safe handling of Isocyanate compounds, feel free to reach out to us on 1300 802 163 or email us at info@anitechgroup.com

minal.metkari

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