In regard to taking on extra work with Job Evaluation it is my understaning that if the task is of a higher grading than your job, you can refuse to do it. If it is of the same or lower grading they can add it to your responsibilities. Obivously if you already have too much work to do this then becomes a staffing issue as you cant do all your work assisgned to you in the time the employer expects.
Like others have said, get advice. Speak to your union for advice on where you stand.
We have an outside company come in and test during the summer.