Environmental audits All our operations are subject to regular internal and external environmental audits, with the below four types of audits performed at Petra: Š Legal Compliance Audits undertaken by external specialists every two years; Š EMP Performance Assessments at our South African operations carried out by external specialists at least once every two years; Š internal Environmental Management Audits performed internally on an annual basis; and Š external ISO certification body, BSI, on certified operations at least once per year.