"Fire ground" is the scene or site of a fire, the place where firefighters do their work. "Deployment" could, in principle, refer to putting equipment into operation, but in this context it normally refers to the functions assigned to the various members of the firefighting team and where and how they work at the scene of the fire: how they are deployed (positioned and put into action):

"Fire fighters will be recruited prior to their fire ground deployment."
http://www.royalcommission.vic.gov.au/Documents/Document-fil...

"NIST Study on Fire ground Deployment
[...]
For the first time, this study investigates the effect of varying crew size, first apparatus arrival time, and response time on firefighter safety, overall task completion, and interior residential tenability using realistic residential fires. [...]
This report presents the results of more than 60 laboratory and residential fireground experiments designed to quantify the effects of various fire department deployment configurations on the most common type of fire - a low hazard residential structure fire. [...] In addition to systematically controlling for the arrival times of the first and subsequent fire apparatus, crew size was varied to consider two-, three-, four-, and five-person staffing. Each deployment performed a series of 22 tasks that were timed, while the thermal and toxic environment inside the structure was measured."
http://www.iafflocal1227.org/