Then after turning on your amp's power, it all depends on how much you turn up your amps volume control and how loudly you play. If the rheostat is truly capable of handling 100W, it may be fine unless you dime the amp's volume and play for a while.
You'll be fine. I had a 5150 up around 5 or 6 running an Airbrake a few times during the recording sessions for my band's demo and it was OK. Just don't turn everything up to ten and use as little attenuation as you can get away with.
Be warned...an amp can put out it's max RMS wattage rating as low as 3 or 4 on the volume control...if it does it could fry the airbrake...I am not saying it will happen but it easily could.