Tell the truth. I wouldn't hold it against you, most people have worked for a mong before and many leave for that reason. In future though always have a new job lined up before walking - it easier to get a job whilst in employment.
I first point I would pick up on is you jumped after they had invested 18 months training you. Why not request another position or a return to your old one [maybe you did]?
You left under circumstances I cannot know, but the fact that you quit without thought to the consequences [eg unemployment], rather than stay on until you found something better would make me question your responsibility.
Sorry if that sounds harsh, but there are normally more potential employees than vacancies and I don't need to take chances or even look on the bright side of application if there is someone else without question marks.
Are you intending to seek work in the same field with another company?
I would suggest to say you faced a moral dilemma that safety was being comprised (you mentioned something bad would happen), you were not listened to, you escalated, no joy and you left to reasons of personal integrity.
I resigned from my job 5 weeks ago, story is; I was totally bored, absolutely no morale in the company whatsoever, different rules for different people etc, but after 6 years you get kind of pi$$ed off. Was looking to develop myself more in the Company, so they brought in an assistant, with a view to handing my job over at Xmas and me moving into another department. I wasn't involved in the interview stage, and what my boss did was hired the thickest bimbo that came for interview (nice chebbs though), after the first week I sort of guessed she couldn't do half of what she claimed on her CV, so I was taking more time showing her basic PC Skills, more or less decided that she was w@nk at the job and spoke to the dumb tw@t who hired her, at which point he stated that we couldn't get rid of her because she was 2 months pregnant
Now I'm all for Equal Ops and all that, by this idiot knew she was pregnant when he hired her, the whole reason in hiring her was so she could take over my role, I sort of guessed that this was no longer going to happen. Anyway, 3 weeks after she started I went on holiday, gave her loads of things to do for when I came back, came back in 10 days later, nothing been done, 600+ E-Mails from irate customers etc, numb nuts says he needs a word and that he's booked a room, (not in that kind of way), so I kind of guessed what it was about, while I'd been away, Little Miss Chebbs has been whining about me, so I printed off all the E-Mails that she'd sent to her mates for the preceding few days slagging the Company and the Staff off, went in armed with everything I could, she'd told him I kept shouting at her, had no patience, gave her no work to do etc, pretty hard for me to shout at her, when we were all in a communal office, anyway, I said to him, either she goes or I go, in fact, fcuk it, I resign!!
Got sent home, brought back in day after, resignation accepted, 4 weeks gardening leave to look for a new job. 3 weeks later, sat at a major competitor, more dosh, more morale etc, etc, etc, and now life's great, but more on topic, this is my excuse for leaving "Group changes, I was wanting a new challenge and amicably resigned with an excellent reference available"
For those of us who leave the mob, it can be difficult to blend into civvy street. They don't understand that we have higher, nay different standards, do the job until it's done, work hard, play hard. If you try to talk to 'them' about it, they think that you are nuts.
There are many employers out there who would love to give you a job - you are the ideal employee - but team fit is the over riding factor and for that reason alone, 9 times out of 10, you won't get the job.
Remember that you are not in uniform anymore and you have to work hard at being a civvy. My best advice to you would be to go it alone. If you are prepared to work 35 hours in 3 days, why are you working for anyone else?
There are a thousand ways to make money and you only need enough to live off and maybe a little bit to stash away to have the life you want. The easiest way is to buy stuff and put it on ebay. It could be anything - clothes to wheel nuts. As long as you are making money it's cool. Then you can spend your own time down the british legion, swinging the lamp, pretending it's the NAFFI. Next thing to do will be joining the masons! Maybe that's for a different thread...
A good book to read is "How to get rich" by Felix Dennis. Costs a fiver and is worth it's weight in gold.