According to a new study by Kathryn Lord and colleagues at UMass Amherst http://www.sciencedaily.com/releases/2009/07/090714210137.htm

"Dogs bark more because they are put into conflicting situations." It was/is widely thought that dogs bark for a number of reasons, such as defending the home front against intruders, or to say "come play with me", just to name two examples. This new study sheds light on an old age question "why do dogs bark?"

I think you answered your own question by using the words 'skittish, unfamiliar, and terrified.' Your dog is in conflict and if not allowed to defuse the situation by creating distance between the people and him, then someone could get hurt and you could get sued. If you are going to try to change his behavior and make him a model citizen, you would work in small increments.

Step one of probably many more steps to come: find someone that the dog likes in a safe place, your home, outside, etc. Feed some great treats by you in the presence of the people. Start at a distance, and then have your friend come closer. This is supposed to be transferred in time to the person, your dog and the work place you described. However, this can be a delicate situation, because you have a number of things that need to change before you should attempt to bring them all together. A new skill set for you and your dog is required and I would find a very good dog trainer, one that will use positive methods to reward quiet, calm behavior and not punish barking around people. If you punish the bark, you are most likely suppressing the conflict and that can lead to a mishap.

At least now you know what is going on with your dog as you described 'constant barking'. I would say take the pressure off, remove your dog, get some great training, and if you find a talented trainer you could even join a group class with a lot going on with people, places and things that would bug a dog. Sometimes dogs can't handle this type of life that you have asked for him, I would say a large amount of dogs cannot for whatever reason. Some dogs will never make a public dog, which is a bomb proof dog in close proximity to people. I think dogs that are in the public in office buildings and have unlimited contact to the world is in essence a therapy dog, somewhat.

There is class and a test for canine good citizens, which I would suggest to help you prepare your dog for public life. Go to AKC.com and click CGC classes and testing sites.