Not all vaccinations will induce a 100% response. I think the non-responder rate for Hepatitis B is somewhere between 5-15%. Usually, the procedure is to offer a second, full schedule - maybe increase it to 3 injections, if memory serves.
As to why you might be a non-responder - hypothetically speaking, one of the reasons why you might be a non-responder is because you are Hep B positive, so they should test for that to rule it out, and to offer counsel relevant to your life and your job if that is found to be the case. Otherwise, you might just not be responsive, and so will be counselled about the safety measures you need to be aware of since you will not have the same level of protection against HepB as others would.
I should not be too worried, amye. See what Occ. Health have to say first, and what the blood analysis shows.