Explanation:

- Employer: The employer is the person or organization providing jobs, but is not typically seen as a 'safety valve' in industrial relations.

- Trade Union: Trade unions represent workers and negotiate on their behalf to solve disputes, but they are not called the 'safety valve'.

- Safety officer: The safety officer manages workplace safety and ensures compliance, but is not usually called the ‘safety valve’ in industrial relations.

- Welfare officer : Welfare officers focus on employee wellbeing, acting as a link between management and workers. They mediate issues, promote harmony, and handle grievances. For these reasons, they are often referred to as the ‘safety valve’ in industrial relations.