Unless the signs of death are unmistakably obvious, such as decomposition, you do not have the right to make that call. Begin CPR following standard resuscitation guidelines. The person may still be recoverable, and it is not your role as a first aider to determine otherwise. If resuscitation is successful, that is an exceptional outcome. If it is not, that determination is made at the appropriate level of care. Do not hesitate, start compressions and keep going until emergency services arrive and take over.
