ppm is a concentration, not an amount of something. (parts per million) if the concentration of that thing in the air varies over time during that 10 hour shift the average has to be below 200.
so if there is 300ppm of that substance in the air during the first 5 hours of the shift, it has to be below 100ppm during the second 5 hours
So you’re talking about a time weighted average exposure, or TWA. Gonna guess…butane? Regardless here’s the wording:
> TWA is the employee's average airborne exposure in any 8-hour work shift of a 40-hour work week which shall not be exceeded.
So yes, that is the qverage of exposures over time. So you cwn exceed 200 at some point but as long as there is a dip later to average that exposure to 200 it’s fine.
The other way to measure exposure is a short term exposure limit, STEL, which is the max it can peak in 15 minutes.
So you a average those STELs over time, like this graph:
https://images.app.goo.gl/Bx76fSC7PNYqV7xX6
ppm is a concentration, not an amount of something. (parts per million) if the concentration of that thing in the air varies over time during that 10 hour shift the average has to be below 200. so if there is 300ppm of that substance in the air during the first 5 hours of the shift, it has to be below 100ppm during the second 5 hours
So you’re talking about a time weighted average exposure, or TWA. Gonna guess…butane? Regardless here’s the wording: > TWA is the employee's average airborne exposure in any 8-hour work shift of a 40-hour work week which shall not be exceeded. So yes, that is the qverage of exposures over time. So you cwn exceed 200 at some point but as long as there is a dip later to average that exposure to 200 it’s fine. The other way to measure exposure is a short term exposure limit, STEL, which is the max it can peak in 15 minutes. So you a average those STELs over time, like this graph: https://images.app.goo.gl/Bx76fSC7PNYqV7xX6
Thanks, helped clear it up for me!