the exposure levels are different for each chemical type–for cancer causing chemicals, for example, no warning is required if the chemical exposure is calculated to result in “not more than one excess case of cancer in 100,000 individuals exposed over a 70-year lifetime.” you can find the prop. it works pretty nicely and simple. i love to display them as well as use them, i just love them. post a comment and share it with us! green and red chili this has been always been my home. 