Re: Kiln Shell Red Spot
how long you can run with a red spot depends on how big the spot is and where in the kiln it is. Sometimes a red spot can be due to a single brick falling out - in such a case it is often possible to put a fan on the area, condense some liquid phase into the hole and run for weeks like this. Bear in mind this coating will fall out following any kiln stop. This can also be done in the case of thin bricks in the burning zone area, and at least gives you time to get s bricking crew organised. Also you can change the flame length to take heat away from the hot area - again will only work temporarily but can give you a few days to organise repairs.
The 'rule-of-thumb' I have often heard is that if you can see the red spot in daylight you should stop pretty much straight away. If it is only a dull glow at night then you can probably manage it for a good while using the above measures.
Maximum allowable temp depends on shell thickness and size of spot but bear in mind once the shell is damaged it all gets very expensive, so best not to run too long with a hot spot. If in doubt - stop it.
In terms of size - much more than a few bricks (~0.5sqm) should be stopped quickly.
Hope this helps