Where the enforcement of Subsection 21-12.4 would entail practical difficulty or unnecessary hardship, or where the circumstances of the case do not require the building or structures to be related to a street, the Board may upon application or appeal, vary the application of Subsection 21-12.4 and direct the issuance of a permit subject to conditions that will provide adequate access for fire fighting equipment, ambulances and other emergency vehicles necessary for the protection of health and safety and that will protect any future street layout shown on the Official Map or on a general Circulation Plan Element of the Borough Master Plan.