A quorum shall consist of four members. The Chairman or, in his absence, the Acting Chairman shall have the power to issue subpoenas to compel the attendance of witnesses and the production of records and may administer oaths. The Board shall perform all the duties and have all the powers provided by law to be exercised by boards of adjustment and shall determine the true location of any district boundary line and in addition thereto, pursuant to the statutes and subject to appropriate conditions and safeguards, shall determine and vary the application of the provisions herein established in harmony with their general intent and purpose to avoid practical difficulties or unnecessary hardships in a manner to secure the public health, safety and general welfare.