From 3M's site.... http://multimedia.3m.com/mws/media/464839O/information-on-isocyanates.pdf
Spraying Isocyanate Paints
Spray painters need to understand the health risks involved in spraying polyurethane paints - these are the two pack mixes of
polyurethane paints and possibly also in the one-pack moisture-cured mixes. These products are widely used in the automotive
and other industries because of their excellent gloss, hardness, adhesion and chemical resistance.
The major hazard with spraying polyurethane paints is breathing the mist or aerosol droplets of the paint spray and absorbing
the isocyanate and other components into your lungs.
The odour threshold for isocyanates, ie the level at which an individual can smell an isocyanate, is typically higher than the allowed
exposure limits. In other words, if a painter smells the sweet, fruity, pungent odour of an isocyanate, they are probably
already overexposed. That is why the recommended respiratory protection for employees spraying isocyanates is a supplied air
respirator and not an air purifying respirator (i.e filter cartridge style). The issue with use of air purifying respirators is that they
will reach a point at which the filter becomes saturated and will no longer capture the isocyanate or other solvents. When that
filter breakthrough happens, an overexposure can occur, potentially causing an irreversible sensitization. Use of a supplied air
system removes this filter change factor - it does not rely on the painter changing his gas/vapour filters at appropriate intervals.
Note: if isocyanate-containing paint is applied by brush, roller or dipping, in a well ventilated area, there is generally no more
hazard than with ordinary paints. These application methods usually do not produce the higher concentrations of isocyanate
vapour associated with spraying.
After curing, polyurethane paints contain no free isocyanates and are not hazardous under normal use. However, welding or
burning of polyurethane coated surfaces can release a range of contaminants.
So, for a small job like a playfield done in a well ventilated area, the cartridge type respirator looks like it should be fine. --- when used with goggles, gloves, & a bunny suit.