139. Subject to Regulations 134 and 142, an employer shall ensure that—

(a) the employer's employees are not exposed to mechanical vibration above the relevant exposure limit value, and

(b) if, despite the measures taken to comply with this Chapter, the exposure limit value is exceeded,

(i) take action to reduce exposure to mechanical vibration to below the exposure limit value,

(ii) identify the reason for that limit being exceeded, and

(iii) amend the technical and organisational measures taken in accordance with Regulation 138 to prevent it being exceeded again.