Depends on the density of the sand storm.
So, lets say we are talking about a forest fire. That is about as bad as a natural fire can get. And for the sake of argument, lets say you have a forest smack dab in the middle of the Iraqi desert.
and lets say this bad boy is the sandstorm
Now, there are multiple aspects to fire. The most popular and well known is what is provided by Ruv Draba's cool pic
However, another less popular aspect is the 'type' of heat radiated by fire. The main reason why forest fires are so bad is due to the radiative heat (IR heat) + conventive heat (hot air/fire). THe radiative heat, that is, energy in the electromagnetic spectrum can heat something to over 1100 degrees F which is more than adequate for combustion. The conventive heat is more direct, removes moisture from the air which makes burning easier. It also carries the heat directly to an object to aid in combustion.
Now, enter the sandstorm.
The Sandstorm would completely dissimate the radiative heat. The particles of sand would absorb the heat and refract the IR radiation all over the place to the point of uselessness.
Now we are left with conductive heat. Likewise, the sand would absorb that too.
Now we are left with Rub Draba's basic chart.
It is my belief that a sufficiently dense sandstorm applied over a long period of time (i.e. hours) would contain a forest fire, prevent it from spreading, and thus, stationary, the fire would burn itself out.
If the density of sand was high enough to equate to a few pounds of sand per square foot, then you have enough to smother the fire.
So the answer to your question is yes. If you have a sandstorm, one of those storms where you can't see your hand in front of your face, then yes, over a period of a 3 hours, it would be sufficient to smother a forest fire. Reason I say 3 hours is that is about how long a log will burn by itself.
The last thing I will say is that the Sandstorm must be greater in scope than the forest fire. If the forest fired covered 100 square miles, then the sandstorm would need to be 400 square miles with a steady flux washing over the forest fire. Essentially, the sandstorm is a heat sink, but a heat sink needs to be big enough to drain the source, otherwise, it is not a heat sink.
Mel...