"Should I be in contact with a lawyer?"
If we're talking the USA here, your "responsibility" might depend on what state you are in. A lawyer might tell you that your status as an employee may protect you from direct legal action. But then again, maybe not.
On a different facet of this: Has your company promoted itself as an engineering company? Has it used the word "engineer" in any descriptions of itself or its services? In many jurisdictions, if they do not directly employ a full time engineer licensed in that state they are actually breaking the law. I know of companies that were shut down for that reason.
Public and human safety are the reasons there are things like design codes for things like buildings, bridges, electrical devices. There are also commonly accepted factors of safety in designing structures or machine members under stress. There are also common testing and prototyping procedures to identify design weaknesses or likelihood of misuse or abuse. "But your honor, we never dreamed that someone would use it like that!"
Bottom line is this: whether its "legal" or not, if you don't feel confident that you can achieve a safe design in the environment you're in, you only have one choice. You know what it is.
I have designed machines that could hurt people for 30 years. There are many opportunities I have turned down. I keep a picture at my desk. Its a removable work platform I designed for temporary access to equipment 40 feet above a hard concrete floor. It was to be installed and removed using an overhead crane. It had locking tabs that guaranteed it was properly attached before workers moved out onto it. Even then the workers were to be tied off. A guy was installing it one night and noticed that it hadn't slipped down fully into the locking tabs. Without tying off he went out onto the platform, which was still attached to the crane, and JUMPED on it to try to seat it. Rather than seating, it flipped over sideways. He was just barely able to grab the handrail and was left dangling 40 feet above the floor. He broke a lot of rules and is no longer employed here. No one blamed me but that would not have made my nights any easier if he had fallen and gotten injured or worse. I would have blamed myself for not foreseeing that possibility. The picture of that platform hanging sideways from the crane remains in front of me to this day as a reminder of the seriousness of my job.
I have worked for bosses like you describe. Sees himself as a "self-made man"? Always confident of success but never willing to take time to consider details? Quickly blames others for his failures? Sounds like the man is a disaster that just hasn't happened yet. Do yourself a favor. Consider this a learning experience and move on to the next one.