The pressure resulting from the blast wave of an explosion referred to as positive when it exceeds atmospheric pressure and negative during the passage of the wave when resulting pressures are less than atmospheric pressure
Defense Technical Information Center DTIF, Glossary (Part I- Abbreviations and Acronyms, Part II- Terms and Definitions), Operations in Chemical, Biological, Radiological, and Nuclear CBRN Environments (Joint Publication JP3-11), Fort Belvoir, VA, USA 2013. http://www.dtic.mil/doctrine/new_pubs/jp3_11.pdf, (DPrepCBRN - Amer) {1021}