Partially because of their sense of purpose, emergency workers are about to develop ptsd than disaster victims.

I believe the answer is:  50% less likely
Soldiers experienced posttraumatic stress disorder commonly because they have to constantly experienced extreme psychological pressure due to a threatening situations or unability to handles guilt that derive from another human being. Since emergency workers do not have to experienced the stress that came because of killing people, the source of PTSD has been reduced to half.