My department is a combination volunteer/paid department. We were conducting live fire trainings at our training centers burn house. I had a volunteer assigned to me for an evolution, so my crew was myself, a career firefighter and this volunteer. Our task was to take a handline to the second floor of a residence to extinguish a bedroom fire. I had the volunteer feed hose from the first floor up the stairs to the second floor where we pulled it to the bedroom. We needed about 5 more feet of hose to reach the bedroom, so I went back to tell the firefighter at the bottom of the stairs to feed more hose. That firefighter was no where to be found. I asked the safety people if they knew where she went, and they said they thought she went outside. I radioed and yelled for her to no avail. I then radioed a MAYDAY and retrieved my other crewmember to start a search. Command never received the mayday, and as we were starting down the stairs, she reappeared and we then put the fire out. I immediately came outside to find out why the RIT standing by was not activated by command. They said they never received a mayday. I knew I heard it transmit over a radio.
What we found out was the firefighter went outside to stretch more hose without notifying anyone. When I transmitted the MAYDAY, I did not push the transmit button hard enough and the radio I thought I heard was my voice amp attached to my mask. I never confirmed with command that they heard the MAYDAY, and that was my fault.