In addition to the natural internal friction that arises from hundreds of people working together, many other external factors which are often outside the control of an individual can contribute to mental and physical stress.
A company thrives when its employees help each other address concerns and overcome obstacles while working towards a common goal. If you observe a colleague undergoing frustration or stress, you would be doing a great service by providing relief, in addition to the obvious warmth of human empathy.
Here are some ways you can identify stressed co-workers:
If you think someone satisfies any of the above criteria, talk to them gently and try to ascertain their difficulty in life. They may need help from a licensed therapist/practitioner, and it is a responsibility to delicately encourage them to seek help if they appear to need it.