They surely mean the temperature inside the Chip at maximum, so if you measure the temp on the heatsink , it´s better to remain much lower than 100 C° or 212 F or 373 Kelvin.
One secure Outside Temp for long run is surley something about 70 degrees Celsius.But this can be realize only with a large Heatsink on the PCB and active cooling. Maybe is better to keep in mind , that one faulty "part" may cause more damage to other parts , for example on my PCB the AME8805 was faulty and gives me 5 V on the output , instead 3,3V ,in worse case the Stm Chip may die due the Overvoltage. So I recomend to be very carefull if you go to the limits. But when i count how much time and money for parts i invest in this Blades, i´m not sure if there will be ever a R.eturn O.f I.nvestment point ever. Maybe if we can sell this huge calculation power for other application , or as a heater for the winter. The only winners in this game are in my opinion only the producers, they can mine at first with this things at a time when this is rentable, and then they sell those things at very high pre order prices. If i spend this time as a taxi driver , i surely earn much more money.....
And who cares about, that now I can repair some G-Blades , no one wants to have them , at the current prices.So much money and time lost.... 
Sorry about this , it´s out of topic and i know that this is the mining game , but it´s really annoying.
One secure Outside Temp for long run is surley something about 70 degrees Celsius.But this can be realize only with a large Heatsink on the PCB and active cooling. Maybe is better to keep in mind , that one faulty "part" may cause more damage to other parts , for example on my PCB the AME8805 was faulty and gives me 5 V on the output , instead 3,3V ,in worse case the Stm Chip may die due the Overvoltage. So I recomend to be very carefull if you go to the limits. But when i count how much time and money for parts i invest in this Blades, i´m not sure if there will be ever a R.eturn O.f I.nvestment point ever. Maybe if we can sell this huge calculation power for other application , or as a heater for the winter. The only winners in this game are in my opinion only the producers, they can mine at first with this things at a time when this is rentable, and then they sell those things at very high pre order prices. If i spend this time as a taxi driver , i surely earn much more money.....
And who cares about, that now I can repair some G-Blades , no one wants to have them , at the current prices.So much money and time lost.... Sorry about this , it´s out of topic and i know that this is the mining game , but it´s really annoying.