Controlling Isocyanate Exposure: A Case Study in Safe Potting Operations

Sysco Environmental Ltd conducted an occupational exposure assessment for hazardous substances at a precision electronics manufacturing facility in Slough. The assessment was requested to evaluate potential exposure to diisocyanates, specifically during potting and mixing operations used in the production of sensor heads.

The facility includes a dedicated potting room where heated diisocyanate-containing compounds are prepared and applied. The work involves decanting, mixing, and dispensing pre-polymers such as TU-401 and TU-801, which contain isocyanate monomers.

What Are Isocyanates?

Isocyanates are reactive chemical compounds commonly used in industrial applications. They are key ingredients in:

• Polyurethane foams (flexible & rigid)

• Adhesives and coatings

• Paint hardeners and surface sealants

• Potting and encapsulating compounds

Types of Isocyanates

1. MDI (Methylene Diphenyl Diisocyanate): Common in foams and potting resins; lower volatility.

2. TDI (Toluene Diisocyanate): Used in flexible foam; more volatile and hazardous.

3. HDI (Hexamethylene Diisocyanate): Found in coatings and paints; known for occupational asthma risk.

4. IPDI (Isophorone Diisocyanate): Used in specialty coatings with similar health effects.

Health Risks of Isocyanates

Isocyanates are potent respiratory sensitisers and a leading cause of occupational asthma in the UK. Once sensitised, a person may suffer severe symptoms at even trace-level exposures.

Acute Effects

• Throat and nasal irritation

• Eye discomfort and tearing

• Chest tightness and shortness of breath

Chronic Effects

• Development of occupational asthma

• Persistent lung inflammation

• Long-term reduction in lung function

Exposure can occur through:

• Inhalation of vapours and aerosols

• Dermal contact, leading to systemic absorption

Monitoring Methodology

Sampling was conducted in accordance with MDHS 25/3, targeting airborne organic isocyanates using treated filter media and personal sampling pumps.

Key Parameters:

• Sample Locations: Potting and mixing areas

• Sampling Duration: Average 50–67 minutes per operator

• Analyte: Methylenediphenyl Diisocyanate (MDI)

• Sampling Rate: 2 L/min per sampler

Monitoring Results

All exposure levels were well below the Workplace Exposure Limit (WEL) of 0.02 mg/m³ (8-hour TWA), with actual concentrations at least 10 times lower.

Control Measures & Recommendations

Ventilation

• Status: Local exhaust ventilation (LEV) was installed, including downdraft benches and semi-enclosed cupboards.

• Recommendation: Fit airflow indicators to LEV systems to allow operatives to confirm functionality at a glance. Conduct 14-monthly LEV testing as per COSHH Regulation 9 and HSG258.

Respiratory Protective Equipment (RPE)

• Status: No RPE currently used.

• Recommendation: Although not currently required, RPE should be considered for tasks involving higher exposure potential or accidental spillage scenarios.

Health Surveillance

• Status: Annual health surveillance programme in place.

• Recommendation: Maintain current programme and include specific symptom tracking for respiratory issues, especially if exposure levels increase in the future.

Training

• Status: General awareness training provided.

• Recommendation: Deliver annual COSHH training covering:

  • The health risks of isocyanates

  • Safe handling and decanting procedures

  • RPE use (if introduced)

  • How to identify control failures or symptoms of sensitisation

Conclusion

Sysco Environmental Ltd confirmed that exposure to methylenediphenyl diisocyanate (MDI) in the potting area is well-controlled and currently poses no significant health risk to employees. However, regular monitoring, enhanced LEV visibility, and refreshed training are essential to maintain these low-risk conditions.

This case highlights how targeted assessments can provide assurance and uncover practical improvements, even where exposures are below regulatory thresholds. In industries using isocyanate-based products, vigilance remains essential due to the high risk of respiratory sensitisation.