Tower Controller issued a take off clearance to an Air Carrier prior to an Airport vehicle reporting clear of the runway; the situation involving an unfolding emergency event and a distracting coordination effort with the TRACON.

Narrative

Aircraft X had just departed about 5 minutes prior and immediately declared an emergency. The aircraft canceled IFR and requested to hold approximately 5 miles south of the airport between 4000-6000. I coordinated the request with Airport Emergency vehicles. I also had cleared an airport vehicle onto RWY 10L to do an inspection. The Approach Controller called to coordinate a point-out on an over flight; a VFR aircraft within the block altitude of the emergency Aircraft X. I instructed the controller to reroute the VFR away from the emergency and basically the coordination turned into an argument. I let the argument disrupt my focus on Local Control. Aircraft Y called ready for take off as they were taxiing on A. I did a runway scan and did not see the airport vehicle. The vehicle had cleared the runway; completing the runway inspection; but had not advised me of clearing yet. I cleared Aircraft Y for take off on Runway XX as they were taxiing and as I did that I scanned again and noticed my Runway Occupied light on the panel was illuminated. I instructed Aircraft Y to hold short of Runway XX and received a good read back. Aircraft Y was still 200 feet from the hold short line on the taxiway. The airport vehicle then called clear of the runway and I cleared Aircraft Y for take off. In the future I will instruct one of the other controllers in the tower to coordinate while I have an abnormal situation (runway closure and emergency) so I can concentrate on the Local position. I think the coordination issue with the Approach Controller caused me to be distracted for that brief moment. I believe I have good scanning techniques on Local and in the end my scan is what allowed me to recognize the situation and stop it.