I can't link to the source of what I stated, but I recall it from shortly after Simoncelli's death.
Folks were saying his helmet should have stayed on.
USDOT helmet requirements:
www.nhtsa.gov/staticfiles/nvs/pdf/TP-218-07.pdfChinstrap test is Section 12.8.
TL;DR summary is the strap must withstand a 136 kilo load for 120 seconds, and must not stretch more than 2.5 cm.
That's 1334 N.
Some Googling unearthed this:
http://www.ncbi.nlm.nih.gov/pubmed/19388771Citing 12 cadaver tests, mean failure load was 3100+/-645 N.
As that was a summary, description of 'failure' was not available.
http://deathpenalty-trial.jp/wordpress/wp-content/uploads/2011/09/Rabl_kaitousho1_eng.pdfCites a value of 12000 N.