Final answer:
OSHA requires that workers work well below the LEL/LFL at the PEL, which is 10.
Step-by-step explanation:
The subject of this question is Health.
The LEL/LFL refers to Lower Explosive Limit/Lower Flammable Limit, which is the minimum concentration of a flammable substance in the air that can ignite when exposed to an ignition source.
In this question, OSHA requires that workers work well below the LEL/LFL at the Permissible Exposure Limit (PEL). The PEL is 10 for the given options. Therefore, the correct answer is option 2) 10.