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In: Tip & Tech |
| TIPS & TECHNIQUES - HEALTH EFFECTS OF ISOCYANATES |
Peeling and Flaking Coating
When a coating loses adhesion to the substrate beneath, peeling and flaking can occur. Flaking is generally termed as the delamination of a brittle coating in small flakes, while peeling generally results in larger areas of the film coming away from the surface.
Peeling and flaking may be the result of insufficient surface preparation and surface contamination.
To ensure optimum adhesion of any coating to a substrate, or existing coating, it is important to ensure that the surface is in a clean, dry condition, free from dust, dirt, wax, grease and surface moisture. Always wear the correct eye protection approved to EN161 and respi-ratory equipment approved to EN149 FFP1S. |
Silicone Contamination
Where silicone sealants have been used and there is contamination to surfaces which need to be sprayed, adhesion of the coatings will be severely compromised. In many cases, it may not even be possible to wet out the surface with the coating, whereas in milder cases the coating may appear to spray out satisfactorily, but will later either pull away from the surface or will peel off quickly under exposure to the water.
Sanding a contaminated surface will only spread the silicone contamination, the only effective treatment is the use of a silicone remover or digester. In severe cases a second treatment may be necessary. |
Coating not Drying?
Failure of a coating to dry in the expected time can be for a number of reasons:
> The drying times for most decorative coatings are usually based on an
average temperature of 20oC. Drying times will naturally vary depend-
ent on the actual temperature at the time of the application and may
be lengthened considerably if the temperature is low. The higher the
humidity, the longer the drying time as this will reduce the rate of
evaporation of the solvent.
> Poor air flow and ventilation will lengthen the drying time of any coat
ing. It is quite possible for an applied coating to remain wet to the
touch after 1 hour or more if it has been applied and then the area
isolated with no air flow. With the introduction of adequate ventilation
the drying process can begin.
> An excessive thickness of coating will naturally take longer to dry than
the recommended drying times stated for a product. The application
of a thick coat instead of a suggested two-coat system is not
recommended. |
Cissing / Fish Eyeing
Cissing is also sometimes known as Fish-eying or when larger areas are exposed it is referred to as crawling.
Cissing occurs when the surface breaks within a wet paint film, exposing the underlying substrate. The paint is unable to wet-out the substrate and “pulls away” from the surface. This sometimes starts with a pinhole and may expand over some minutes to the eventual ciss.
Cissing is normally the result of surface contamination by either, moisture, grease, or silicone. It can be prevented in many cases by degreasing the substrate prior to coating using thinners or thinner on a clean, lint-free cloth. Dampen the cloth with the solvent and wipe over the surface, changing the face of the cloth frequently and allowing the solvent to evaporate before overcoating. In cases of silicone contamination, a silicone remover should be used. |
Health Effects of Isocyanates
Isocyanates are highly reactive chemicals typically found in the hardener
of two-part paints and primers. Isocyanates are present in two forms,
monomer and prepolymer. The isocyanate monomer content is
frequently indicated in Material Safety Data Sheets (MSDS), but this is
only a small part of the total unreacted isocyanate present. Both forms
of unreacted isocyanate are a risk to health when they are released into
the air during paint or primer spraying.
Breathing unreacted airborne isocyanate can cause coughing, chest
tightness, fever, fatigue and sensitization. Many cases of isocyanate-
related sensitization have occurred in Saskatchewan. Once a worker is
sensitized, further exposure to even very small amounts of isocyanate
will cause distressing asthma-like reactions. The reaction may occur
immediately or several hours after exposure. One exposure to a high
airborne concentration or several exposures to lower concentrations may
result in sensitization. There is no proven method for predicting whether
any particular person will become sensitized if exposed to Isocyanates.
Direct skin contact with isocyanates may cause rashes, blistering and
reddening of the skin. Repeated skin contact may cause skin sensitiza-
tion.
Eye exposure to airborne isocyanates can cause eye irritation and
temporary blurred vision. Direct contact with the eye may cause
damage to the cornea.
Isocyanate Painting
All spraying of isocyanate paints must be done in a commercial or
engineered paint booth, or one that is acceptable to the local fire authority.
The painter must wear an airsupplied respirator. |
Isocyanate Priming
Although primers contain less isocyanate than paints, they must be
applied in a paint booth unless there is a separate shop area which
meets the following criteria:
> The shop area must be separated from the rest of the shop by a
barrier or screen.
> The shop area must be equipped with an explosion proof ventilation
system.
> The barrier or screen and the ventilation system must cause air to
move from adjoining areas into the priming area. This will prevent
airborne isocyanates from entering areas where workers are not
protected by air-supplied respirators.
> If there is any risk of fire, the employer must consult with the local
fire authority about the acceptability of the shop area. Things that
might create a fire hazard are: 1) the quantities of paint applied;
2) the method of application; 3) the location of the priming area; or,
4) the materials used in the construction of the priming area.
> The person who applies the primer must wear an air-supplied respira-
tor. Even short duration priming tasks release unacceptably high
levels of airborne isocyanate. Low-pressure spray guns release less
airborne paint, but levels are still high enough that only air-supplied
respirators provide sufficient protection.
Paint Mixing and Cleaning
Paint mixing areas must have sufficient ventilation to prevent the build-up of airborne solvent. There is not enough unreacted isocyanate released during mixing to require the wearing of air-supplied respirators; however, a face shield should be worn where there is a risk of splashing paint into the eyes. Gloves should be worn to prevent skin contact. A cartridge-type respirator with organic vapor cartridges may be worn to reduce the amount of paint solvent breathed.
While cleaning spray guns by passing solvent through the gun under pressure, air-supplied respirators must be worn since unreacted iso cyanate may be released into the work environment. |
Air-Supplied Respirators
Workers must always wear air-supplied respirators when spraying paints
and primers containing isocyanates. Other types of respirators do not
provide adequate protection for workers spraying isocyanate paints and
primers.
Air-supplied respirators approved by the United States National Institute
for Occupational Safety and Health (NIOSH) as type C constant flow
or pressure demand are accepted by the Division for use with isocyanates.
The Division will accept air-supplied respirators approved by
testing agencies other than NIOSH in some situations. (Ask respirator
suppliers to provide a letter of acceptance issued from the Division for
any respirators that do not carry NIOSH approval.)
Breathing air for the painter’s air-supplied respirator must be clean.
A non-oil type electrical compressor specifically designed for providing
breathing air is the best choice. Compressed shop air may be used if
filters are provided to remove water, oil and he breakdown products of
oil. The compressor must be kept in good repair. Overheating of the
compressor must be prevented so that carbon monoxide will not be
produced. Only clean air can be used to feed the compressor. The
source of the air must be distant from vehicle exhaust to avoid unaccept-
able carbon monoxide levels in the air breathed by the painter.
The breathing air must be supplied to respirators with tight fitting face-
pieces at a rate of at least 115 liters per minute (4 cubic feet per minute),
and of at least 170 liters minute (6cfm) to respirators with loose fitting
facepieces. The air supply rate should not exceed 425 liters per minute
(15cfm).
The airline feeding the spray gun may be split to also feed the supplied-
air respirator as long as the air is filtered in the prescribed manner and
supplied at the prescribed flow rate.
Skin Protection
Full coveralls are required when spraying isocyanate paints and primers.
Synthetic rubber or PVC gloves must be worn. These materials prevent
isocyanates from reaching the skin.
Consult MSDS (Material Safety Data Sheets) for additional hazard information |
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