Aromatic isocyanates - TDI / MDI
This page brings together the main information on aromatic isocyanates, more precisely Toluene diisocyanate (TDI) and Diphenylmethane diisocyanate (MDI), their physical characteristics, their health effects, the detection means (aromatic isocyanate gas detector) as well as suitable respiratory protection equipment (gas mask or PAPR with type E-P2 combined filter).
Aromatic isocyanates (TDI - MDI) properties
Aromatic isocyanates are used today in polyurethanes synthesis. Toluene diisocyanate, also called TDI, is used mainly in flexible padding foams manufacturing. Diphenylmethane diisocyanate, also called MDI, is useful in the production of rigid foams for insulation and can also be used as a binder in foundries.
| Gaz | CAS | TWA (8 hours) | STEL (15 minutes) | LEL | IP | Density / Air | Filter / SCBA |
|---|---|---|---|---|---|---|---|
| TDI | 26471-62-5 | 0,01 ppm | 0,02 ppm | 0.9 % | - | 6 | A2B2, P3 |
| 4,4'-MDI | 101-68-8 | 0,01 ppm | 0,02 ppm | - | - | 8.5 | A, P3 |
Aromatic isocyanates effects on health
TDI (Toluene Diisocyanate) is a colorless or pale yellow liquid with a pungent, penetrating odor detectable at low concentrations (in the 1 to 2 ppm range). 4,4'-MDI (Diphenylmethane diisocyanate) shapes as white or pale yellow crystals with a faint musty odor.
Acute exposure to TDI and MDI isocyanates causes damage to the respiratory mucous membranes which can be severe. Irritation of the skin and eyes can also be particularly severe. Chronic exposure to TDI can cause occupational asthma, as well as an accelerated decline of the respiratory function. Repeated MDI exposure results in allergic manifestations: eczema, asthma, hypersensitivity pneumonitis, conjunctivitis.
TDI effects on health (Toluene diisocyanate)
Short exposure at high concentrations, MDI can cause reactions that may only a few hours after: irritation of the mucous membranes (conjunctivitis, rhinitis, pharyngitis, nausea, vomiting), skin irritation, pulmonary irritation (chest pain, cough, etc.), neurological disorders (dizziness, disturbances of balance and consciousness, headaches) and in the most serious cases pulmonary edema.
In case of repeated MDI low concentrations exposure, reactions may appear a few weeks to several years later: contact eczema, allergic asthma or even hypersensitivity pneumonitis.
Aromatic isocyanate detectors (TDI MDI)
Few equipment is available for monitoring aromatic isocyanates: passive chemical detection  badges to be worn by employees, or a much more complex (expensive) optical gas analysis device.
Aromatic isocyanates respiratory protection (TDI MDI)
As isocyanates are very irritating to the eyes and to the respiratory tract, it is recommended to opt for a full face mask for short interventions, or in rooms with a low gas concentration or for a powered air purifying respirator (more comfortable), with A2B2-P3 combined filters for TDI or A-P3 for MDI. In case of emergency interventions, a self-contained breathing apparatus will be imperative.