Brilliant Gary - thanks for posting that. I love a good bit of engineering in a photo/video
I wouldn't go anywhere near one of those events Jay. The holi powder used in the colour run events is normally rice flour mixed with food colouring. It would probably have a temporary effect if you breathed it in (or maybe you'll make dough in your lungs....

) but you'll recover in a few days. However, as with anything these days, unscrupulous people will make it out of anything they can lay their hands on and everything from heavy metals to ground glass has been found in these powders. Check out this medical report of one 10 year old boy in Mumbai:-
http://www.pediatriconcall.com/Jour...d=280&type=T&tid=18&imgid=&reportid=&tbltype= He did make a full recovery (ie had no symptoms) after 3 days or so, but who knows what else will become apparent later on in his life.
Poster paint is normally made from chalk (backintheday it may have been made from white lead) and is not hazardous although of course you'd still cough it up for a few days if you breathed it in. Here's the data sheet on Reeves poster paint:-
http://www.artifolk.co.uk/images/resources/12828ReevesTemperaCOSHH.pdf
Particles like glass fibre, metal, glass and asbestos on the other hand can lodge themselves in the soft tissue in your lungs, and cause abnormal growth and mutation, cancers etc Concrete contains Chromium and Silica, and repeated exposure to concrete dust can cause silicosis and may also cause cancer.
So I think these guys were ok if that powder is poster paint, but I agree - you should wear a mask!
Water cooled LEDs

You can get 1200 lumens out of one CREE XML2-U2 chip now, without water cooling: just a moderate heatsink will be enough for a few minutes run. I wonder how many of those I can get on an aluminium CPU cooling block with a 120mm fan on it?

Also love the big rubber membrane he made to "explode" the powder - and big extractors to shape the plume of dust. Great video.