Fire Division 1 - Mass explosion.
It's the equivalent to <a href="https://en.wikipedia.org/wiki/ADR_(treaty)" class="extiw" title="w:ADR (treaty)">Dangerous Goods transport treaty (ADR)</a> class 1.1 and 1.5.
<a href="//commons.wikimedia.org/wiki/User:The_Navigators" title="User:The Navigators">The Navigators</a>
<a rel="nofollow" class="external text" href="https://www.wbdg.org/FFC/DOD/DODMAN/605509-M-V1.pdf">DoDM 6055.09-M-V1, February 29, 2008</a> Page 53.