A PEL of 10 ppm indicates that ?

a) 10 parts per million of this substance in the air is enough to kill you

b) the maximum allowable workplace air exposure to this substance for an adult worker for 8 hours a     day, 40 hours a week, for a year is 10 ppm

c) 10 parts per million of this substance in the water is safe for the average adult

d) the maximum allowable workplace air exposure to this substance for an average healthy adult worker     for 8 hours a day, 40 hours a week, for a working lifetime is 10 ppm ACS