From a workplace perspective, how do you deal with personal issues? 

First, if you trust your boss at all, sit down with him or her in a room where you can close the door and tell enough about what is going on so that he knows you are stressed. Ask him if he can give you some time off or if not, work with him to reduce the level of workplace stress by moving some tasks to someone else.  Most bosses will appreciate knowing there is an issue to be worked around before deadlines are missed and work is done incorrectly and especially if there is any kind of a workplace safety issue as a possibility (which I assume there could be in the chemical industry). 

From what you describe as your current state, a few days off will probably be as much to the company's benefit as yours. 

I know some people prefer to keep their private issues private, but you will get much more support from the boss and HR (if need be) if they know the situation. Make sure to ask that the information be kept confidential or that you tell them what they can let others know and what they cannot. 

It may be the nature of the type of places where I work (not all are supportive I am well aware and the lower you are in the organization the less supportive they may be), but I have seen far more people get into trouble of the reprimand/firing type by not disclosing a personal issue and their work suddenly falling of than those who do bring it up and get help from the organization in managing it. Often, the worst action you can take when your work is being affected by a personal issue is not leveing with your boss about it as soon as possible.

If you are a good worker and they know what the situation is, most workplaces will try to make accommodations to keep you working through the crisis or to give you the time off you need to deal with it  Or both). Truly I was amazed by the amount of help I got from the organization for the whole year that my performance was affected when my spouse died.  

If you are not a good worker, you are less likely to get as much support (but probably still will in the really big issues like a cancer diagnosis or a the death of a child or a spouse). The company has little vested interest in keeping you when your performance goes down if it is already not acceptable.

Human Resources people can also be a huge help when your personal life has unavoidable stresses. I know when my spouse died, the HR person really helped me by pointing me to the benefits I could take advantage of such as the EAP and bereavement leave. 

I don't know the nature of your personal problem, but it still might be helpful to talk to someone in HR about anything that could be impacted by the situation (for instance, in a divorce, they could help you figure out all the things like insurance beneficiaries, etc, that you need to change.)  

I know when a co-worker had cancer, the HR people helped her through the process of getting short-term and long-term disability (think about it, do you know how to get these benefits activated when you need them even though you are paying for them in your paycheck?) HR is mostly best for personal situations where there might be an impact somehow on your benefits.

Because you are distracted and upset, you might want to have someone else do a look over of your work. Mistakes are much more common when you are stressed and having a second set of eyes can only help. It also shows management that you are aware that the work still needs to be done and done right even when stressed. 

Your office may have an Employee Assistance program, this is the kind of situation that these programs are designed for, so take advantage of them. 

On a personal note, it really might be helpful to get some professional counseling. It is hard to get through major crisis. There is nothing wrong with needing some help.