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Polyurethane paints and lacquers


Polyurethane paints and lacquers fall into the following three categories:

  1. Urethane oils and urethane alkyds (e.g. polyurethane varnishes):
    Urethane oils and alkyds contain no residue of free unreacted isocyanate and thus the handling and use of these products is no different to normal solventbased paints.

  2. Blocked isocyanates (e.g. some soldering fluxes):
    Blocked isocyanate coatings also contain no residue of free unreacted isocyanate, and thus the application of these materials poses no problems from that viewpoint. However, phenolic solvents may be present in the formulated paint and additional phenolic material may be released during heat curing processes. In these circumstances appropriate precautions for phenols must be taken. These must include protection (adequate ventilation and/or respiratory protection against inhalation of phenolic containing vapours and suitable protective clothing to prevent skin contact).

  3. Polyisocyanates (e.g. one pack moisture-cured and two-pack iIsocyanate containing paints):
    The great majority of industrial-used polyurethane coatings contain polyisocyanates. This section is concerned with precautions to be observed in the handling and application of these materials. The two most important isocyanates are toluene diisocyanate (TDI) and 4.4.1 diphenylmethane diisocyanate (MDI).

Mixing:

  • The mixing of these paints should be in well ventilated areas with the appropriate respiratory protection worn.

Application by brush or roller:

  • Where MDI class materials are applied by brush or roller, there is unlikely to be a problem from exposure to free isocyanates unless ventilation in the area is inadequate.
  • Where TDI class materials are applied by brush or roller the area shall be well ventilated and ori-nasal canister respirators worn. If there is doubt about the effectiveness of the ventilation then positive pressure air-supplied respirators must be used.

Application by spraying:

  • If you are a spray painter, you need to understand the health risks involved in spraying polyurethane paints and know how to protect yourself against them.
  • The liquid paint, which comes out of a spray gun, is in a fine mist called an aerosol. If you inhale this aerosol, the liquid isocyanate is absorbed into your lungs, and this is when health problems can start.
  • Breathing the aerosol of isocyanate-containing paint causes irritation of the nose, throat and lungs. This can happen either immediately on exposure or, more often, later. The symptoms are a dry or sore throat, coughing, wheezing, chest tightness and/or asthma.
  • Eye contact causes irritation; it may also cause severe chemical conjunctivitis.
  • Skin contact causes mild irritations which can lead to dermatitis.

Precautions to be adopted for spraying and drying of sprayed articles:

  • All spraying and the drying of sprayed articles shall be carried out in accordance with the requirements of the Regulations.
  • The spraying of all isocyanate-containing paints must be carried out in a properly designed and constructed spray booth.
  • The mechanical ventilation system provided must be interlocked with the air supply to the spray gun.
  • When operators, whether spraying or not, are required to work inside a spray booth whilst spraying is in progress, they shall wear an airline respirator.
  • The compressed air supply for the respirators must be taken from an uncontaminated source.
  • In addition to the recommended respiratory and eye protection, spray operators shall wear gloves and a head covering in the case of respirators which leave the hair exposed.
  • Mechanical ventilation of the booth must be maintained after spraying ceases until the work area is free of all residual spray mist.

Isocyanate over-exposure:

Symptoms include:

  • Sore eyes
  • Running nose
  • Sore throat
  • Coughing
  • Wheezing
  • Fever, breathlessness and cough

First aid treatment:

Inhalation:
This may be either from the vapour or from an aerosol. Remove the affected person to fresh air. Keep at rest. Obtain immediate medical attention.

Eye contact:
If isocyanate has entered the eyes, flush them immediately with direct mains water or sterile water from an eye wash bottle for at least 15 minutes, holding the eyelids apart. Obtain immediate medical attention.

Skin contact:
Wash the skin immediately with copious amounts of water and soap (if available). Remove heavily contaminated clothing immediately. Obtain medical attention if skin dermatitis appears.

Ingestion:
DO NOT induce vomiting. If the person is conscious, give between 250ml and 500ml of milk or water to drink. Take to hospital without delay. DO NOT give anything by mouth to an unconscious person.

Removal of polyurethane paint:

Sanding down:
When isocyanate paints are fully cured, if they have been applied for more than 24 hours at room temperature or heated for one hour at 70°C, and are sanded down, the dust produced will not present an isocyanate hazard. This is because fully cured paints contain no free isocyanates. In such instances a dust mask should be worn to provide protection from the general nuisance dust present. Where new paint that may not be fully cured is sanded down, the dust will contain free isocyanates.

A particulate respirator fitted with Class H filters should be worn. Where practical, the use of wet sanding methods is recommended as a means of reducing the amount of dust generated.

Personal hygiene:
This is important in any industry where harmful chemicals are used. The basic rules are common sense:

  • Wash all splashes of paint or lacquer off your skin at once with soap and water. Try to avoid using solvents as much as possible.
  • Do not keep food or eat or drink in the work area.
  • Do not smoke in the work area, or if you have paint on your hands.
  • If possible, shower before you change into your street clothes.

The employer's responsibilities:
The employer must instruct workers on the hazards of working with isocyanate-containing paints and how to use them safely.

The employer is also legally required to provide all the necessary safety equipment.

The employee's responsibilities:
Employees have a duty to use all the safety gear the employer provides. Employees owe it to themselves to protect their health - and the job they have spent years learning.

Spillage procedure:

In case of spillage:

  1. Put on protective equipment.
  2. Cover spillage with absorbent material such as sawdust.
  3. Pour on decontaminant mixture, a quantity estimated to be twice the volume of the spill. Refer to 'Approved Code of Practice of the Safe Use of Isocyanates'.
  4. Allow at least 10 minutes for the decontaminant to react.
  5. Collect all residues from the spillage and place them in an open container.
  6. Add further decontaminant mixture to this material, place a loose cover over the container and remove it to a safe place. Discard residues after one day.
  7. Wash down the area with liquid decontaminant.
  8. Rope off the area and post 'No Smoking' signs.
  9. Clean and decontaminate safety equipment.

Related booklets available from OSH:

  • Approved Code of Practice for the Safe Use of Isocyanates
  • A Guide to Respirators and Breathing Apparatus
  • Guide to the Spray Coating Regulations
  • Welding Safety
  • How to use Isocyanates Safely (A bulletin for spray painters).
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