When working with dangerous chemicals, you should always research what you will be exposed to and how to best protect yourself from it. Here is a question about working with a dangerous chemical:
Does 3M make a respirator cartridge for isocyanate?
For the sake of this discussion, I think it is important we all know a little bit about isocyanate. It is a powerful irritant of the mucous membranes, the gastrointestinal tract, and the respiratory system. You can neither smell nor taste the isocyanates so there is no way to know whether or not you have been exposed.
Isocyanates are also sensitizers. This means though your first reaction may have been mild, subsequent exposures will become more and more severe. Some reported sensitized reactions have been so severe that they resulted in death. Isocyanate is not something to mess around with.
It is said that you may use the organic vapor cartridge 6001 for a brief period, but this period is not specified, and depends on the concentration. Since you can neither smell nor taste the isocyanates, there is no possible way of knowing that breakthrough has occurred.
For this reason, PK Safety does not recommend the use of cartridges for isocyanates. Instead we recommend using the Allegro airline respirator. This will deliver you fresh air from outside of the work area instead filtered air from your immediate vicinity. This is the only real way to ensure that you are not exposed to isocyanates.
When contending with isocyanates, or any other dangerous chemical for that matter, safety should be your first concern. Don't take the risk; get the proper protection.