C182 INSTRUCTOR AND STUDENT HAVE RWY INCURSION AFTER ANNOUNCING ON CTAF FREQUENCY INTENTIONS TO CROSS WITH VOLUME TOO LOW. NEAR GROUND COLLISION WITH DEPARTING ACFT OCCURS.

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THE FLT WAS INSTRUCTIONAL TO PREPARE MY CUSTOMER FOR THE CFII RATING. OUR ACFT WAS A C182T WITH AN AVIONICS SUITE. I WAS IN THE L SEAT AND THE CUSTOMER (WHO WAS PIC) WAS IN THE R SEAT. AFTER REFUELING; WE STARTED THE ENG AND COMPLETED OUR COCKPIT SET-UP. THIS ACTIVITY INCLUDED CHKING THE ATIS FOR NEARBY ARPT. THE TAXI RTE FROM THE FUEL PUMPS TO THE RUN-UP AREA FOR RWY XX REQUIRED THAT WE CROSS THE RWY AT MIDFIELD TXWY B. AS WE APCHED THE RWY; BOTH OF US LOOKED BOTH WAYS DOWN THE RWY TO ENSURE IT WAS CLR. MY CUSTOMER ANNOUNCED OUR INTENTIONS TO CROSS ON THE CTAF FREQ WITH NO REPLY. DURING THE INSTRUCTIONAL FLT; WE DISCOVERED THE VOLUME ON THE #1 COMS RADIO WAS TURNED ALL THE WAY DOWN WHEN WE ATTEMPTED TO CONTACT THE CTL TWR AT A LCL ARPT FOR A PRACTICE ILS APCH. THE RADIO WAS OPERATING NORMALLY. AFTER AN UNEVENTFUL FLT; WE WERE MET BY FLT SCHOOL PERSONNEL WHO INFORMED US THAT WE HAD COME VERY CLOSE TO COLLIDING WITH ANOTHER FLT SCHOOL AIRPLANE WHO WAS TAKING OFF AS WE CROSSED THE RWY. WE WERE TOTALLY UNAWARE THAT THIS HAD OCCURRED. TALKING WITH THE INSTRUCTOR AND CUSTOMER OF THE OTHER AIRPLANE; THEY SAID THEY HAD ALREADY BEGUN THEIR TKOF ROLL AS WE ENTERED THE RWY. THEY MADE REPEATED ATTEMPTS TO COMMUNICATE WITH US ON THE CTAF FREQ WITH NO REACTION. THEIR ONLY OPTION WAS TO CONTINUE THE TKOF; WITH THEM PASSING AN ESTIMATED 30 FT OVER OUR AIRPLANE. THEY STATED THAT THEY WERE PRACTICING A SHORT FIELD TKOF AND THAT IF IT HAD BEEN A NORMAL TKOF THEY WOULD HAVE HIT US. A REVIEW OF THE POH TKOF PERFORMANCE DATA FOR THEIR AIRPLANE CONFIRMED THIS. AFTER DISCUSSING THE INCIDENT; MY CUSTOMER AND I CONCLUDED THAT WHEN HE CHKED ATIS USING THE #2 COM RADIO; HE TURNED THE VOLUME DOWN ON #1 COM AND FORGOT TO TURN IT BACK UP. NEITHER OF US CAUGHT THIS ERROR. THE SYS COMBINES THE CTLS FOR THE #1 AND #2 COMS. UNLIKE MANY ACFT RADIOS; THE VOLUME KNOB IS NOT MARKED TO GIVE A VISUAL INDICATION OF THE RELATIVE VOLUME. THERE IS A DISPLAY OF PERCENT OF VOLUME ON THE EFIS DISPLAY WHEN VOLUME IS BEING ADJUSTED; BUT THIS DISAPPEARS A FEW SECONDS AFTER THE ADJUSTMENT IS COMPLETED. FURTHER; THE SAME VOLUME KNOB IS USED TO ADJUST VOLUME FOR BOTH COMRDOS. ANOTHER FACTOR WAS EXPRESSED BY THE FLT SCHOOL CHIEF FLT INSTRUCTOR. HE INDICATED HE HAS NOTICED THAT A WHITE FENCE JUST N OF THE APCH END OF RWY XX CAN HELP MASK THE ABILITY TO SEE A WHITE AIRPLANE AS IT BEGINS ITS TKOF ROLL WHEN VIEWED FROM THE MIDFIELD TXWY. WHILE BOTH OF US WERE ALERT AND LOOKING FOR OTHER TFC WHEN XING THE RWY; AND OBSERVING STERILE COCKPIT PROCS; IT IS CLR THAT THIS INCIDENT WOULD NOT HAVE HAPPENED IF WE HAD TURNED THE VOLUME OF THE #1 COM BACK UP AFTER CHKING ATIS. I BELIEVE THE DESIGN OF THE VOLUME CTL MAY HAVE CONTRIBUTED TO THIS ERROR. AWARENESS OF A POTENTIAL OPTICAL ILLUSION WOULD ALSO HAVE HELPED; AND THE FLT SCHOOL IS PREPARING A NOTICE TO ALERT ALL INSTRUCTORS AND CUSTOMERS OF THIS EFFECT. I ALSO BELIEVE THAT IF THE AIRPLANE ON TKOF ROLL HAD BEEN USING ITS LNDG LIGHT; WE WOULD HAVE BEEN MORE LIKELY TO SEE IT. FLT SCHOOL POLICY REGARDING USE OF THE LNDG LIGHT DURING ARPT OPS IS UNDER REVIEW.