I worked in that field for 10 years, and this is my opinion:
You have to be highly adaptable- for recruitment, the ability to read people, to know what personalities fit well and work well together, to be able to decifer personalities reasonably well. The ability to motivate and get people excited about what they do, to create a positive work environment- you would be surprized how much the person that occupies this role effects the organizations culture.
Very detailed and analytical- the labour relations part of the job, but compassionate at the same time, flexible to bend rules for those that need it. For instance deciding to extend Long Term Disability for someone who is fighting cancer.
Very comforting but extremely knowledgeable- you deal with everything from alcoholism to suicide, you are the one that the employees look to for comfort when a fellow employee commits suicide, you are the one the family meets with afterwards to get benefits straightened out, you are the contact person that the insurance company calls.
Empathetic- it is so easy to forget what it is like for those that are unemployed that call you for a job, or interview for a job with you. It is so important to be compassionate.
For the safety aspect- you have to be hard nosed, anyone breaks those rules and it is serious because peoples safety is on the line, but approaching it the right way is very important too, you want to motivate them to be safe, create a safety conscious culture not go around like a police officer ramming the law down their throats.
Very organized, lots of charts, lots of paperwork- you have to practice due dilligence there is so much at steak yet flexible enough to enjoy a job with many different avenues to it, some of the avenues very different then others.
Then there is the union work- you need to know your legislation well but create a positive relationship with the union yet maintaining the companies integrity
The biggest challenge I found was not to get wrapped up in others issues- alcholism, or other sad issues because if you do it is hard to do your job objectively.
Hope that helps,