Again, interesting comments. I am working on the figure of 300mg. However, if you start to seriously research the subject you start to come across anomalies. A lot of the "organisations" state that pilots "should be aware" and "recommended that pilots treat with caution" when using caffeine. I never spill mine! But try to get actual figures with a definitive authority behind them is hard. I have read books and articles and all differ. Why I believe it is so hard to answer is for several reasons 1. No in-depth serious research has been carried out into caffeine 2.Caffeine is now in so many types of food, drink and medication and 3. The physiology of the individual makes it difficult to compute (we are all different...but the same!) along with the individuals activity. So, still looking for that definitive answer!
However, caffeine CAN be fatal. In March this year (2017) a fit and healthy 16 year old drank a "fizzy" soft drink, a Café Latte and a can of Red Bull all within two hours died of cardia arrhythmia brought on by the large intake of caffeine over a short period of time. Conversely, like you guys I know a lot of people that if you cut their veins they bleed coffee and "appear" to be okay. Physiology, I believe, is the reason why authorities in the aviation field are reluctant to put figures on the dosage, its just too hard for them to call and theirs no money in it! By the way, 100g of caffeine WILL kill you! Many thanks to all, still interested in your thoughts etc and DONT SPILL THE COFFEE!