The Body, through the Zoning Officer, shall give notice of the time, place and purpose of public hearings to be held by it on proposed amendments or supplements, by mailing a postal card or letter notice to the owners of all properties lying within 200 feet of any part of the property proposed to be changed. The failure to notify as provided in this section, shall not invalidate any recommendations adopted hereunder; it being the intention of this section to provide, so far as may be possible, due notice to the persons substantially interested in the proposed change that an application is pending before the Body, proposing to make a change in the Zoning Map or the regulations set forth in this chapter. In the case of storage of explosives, in addition to the above, property owners within 500 feet of the structure in which the explosives are stored, shall also be notified.