Rather than confuse you with terms like flash point and vapor pressure let me try to put in a perspective that is more easily understood.
Hexane is a member of a class known as aliphatic hydrocarbons. It is named for the number of carbon atoms which is 6. The first 5 members of the family are gasses. Methane with 1 carbon, ethane with 2, propane with 3, butane with 4, pentane with 5. Hexane with 6 is a quasi liquid-gas. Octane(gasoline) has 8.
Hexane doesn't burn, it explodes.
Lets just ignore the exposure limits.
I sense that you have another agenda.
Even if he were dumping the material (an accusation for which there is no proof at this time) the ecological impact would be minimal and transient.
He claims that there is no hazardous waste problem. I believe him. Given the size of his factory and its annual sales, I would be surprised if he were not a Conditionally Exempt Small Quantity Generator. There is likely no "there" there.
Additionally, this is not a process that generates a lot of "sludge". He is likely removing small amounts of cutting oils from each part. He could likely operate nearly forever before he accumulated 1000 kg of hazardous sludge.
Hexane is a HAP, but the plant appears to be below reportable limits, and at best (or worst) he would be a Synthetic Minor source under Title V. And apparently his usage is small enough that he falls below TRI reporting thresholds.
As for the exposure of his workers, the PEL is 500ppm. No one is claiming that he has exceeded that level. And in any case, that is not any concern of the EPA.
As for maintaining safety from explosion, the LEL for hexane is around 12,000ppm. With a PEL of 500ppm, your concern that this man is in imminent danger of lofting his plant into low earth orbit, with all his employee inside, would seem to be a bit misplaced. The ventilation system for maintianing health would, by deninitions, also be maintaining safety.
If everyone who exposed their workers and the workplace to chemicals that had an LEL of 12,000ppm has their asses whippd and were then thrown in jail, there would be an awful lot of people in jail with whipped asses.