Working Conditions
Are the working conditions in which you are requiring your employees to work increasing their stress?
Is the employee being required to work in excessively hot conditions?
Are they exposed to constant interruptions?
Are the welfare facilities appropriate?
Is there a high level of confrontation?
Etc.
These may all be within legal requirements when considered individually however may contribute to the employees stress and form part of the case for a claim for damages against you as their employer. Training may well become an issue, e.g. employees working in Customer Care dealing with angry customers.