When the internal audit staff lacks the necessary skills for a specific audit, such as reviewing controls around the disposal of chemical waste, the most appropriate approach is to assemble a team of internal auditors and consult with an external expert on chemical waste disposal. This ensures that the audit is conducted with the requisite level of technical expertise and objectivity, supported by professional guidance. This approach is in line with best practices that recommend leveraging external expertise when internal competencies do not meet the specific needs of an audit.

The Institute of Internal Auditors (IIA) - International Professional Practices Framework (IPPF), specifically guidelines on using external experts in audit engagements.