…If the fire is small and contained.
The time to use a fire extinguisher is in the early, or incipient, stage of a fire. Once the fire starts to grow or spread, it is best to evacuate the building, closing doors or windows behind you.
…If you are safe from toxic smoke.
If the fire is producing large amounts of thick, black smoke or chemical smoke, it may be best not to try to extinguish the fire. Neither, should you attempt to extinguish the fire in a confined space. Outdoors, approach the fire with the wind at your back. Remember that all fires will produce carbon monoxide and many fires will produce toxic gases that can be fatal, even in small amounts.
...If you have a means of escape.
You should always fight a fire with an exit or other means of escape at your back. If the fire is not quickly extinguished, you need to be able to get out quickly and avoid becoming trapped.
…If your instincts tell you it’s OK.
If you do not feel comfortable attempting to extinguish the fire, don’t try get out and let the fire department do their job.