HSE enforceable regulations to protect workers from substances hazardous to health. Substance means any solid, gas, fume, dust or vapour and any micro-organism. The employer must, inter alia, assess, monitor and control each work situation to ensure that workers are not exposed to possibly harmful amounts of any substance connected with the work. COSHH sets out limits for a large number of hazardous substances based on maximum exposure limits and occupational exposure standards. The employee has a duty to cooperate with the employer regarding monitoring and health surveillance.