Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Flight Deck / Cabin / Aircraft Event Illness / Injury
Flight Crew Returned To Gate; General Maintenance Action
Aircraft
After landing in ZZZ while taxiing to the gate we turned on the APU. We left the APU on after engine shutdown to keep the cabin warm due to the below zero temps in ZZZ. We discharged the passengers; fueled up; loaded up; closed the doors and pushed back from the gate.During the pushback we started the engines as normal. After the engine were started and the tug was disconnected we ran our after start checklist and began taxiing out to Runway XX. We left the APU on since the takeoff performance required the ECS (Environmental Control Systems) to be off and I wanted to keep the cabin warm due to the cold temps.About 30 seconds into the taxi I started to notice some sort of burning smell. I couldn't quite place it; it didn't seem to be exhaust; it wasn't an electrical fire smell or smoke; it almost smelled like burning brakes or clutch from a car. It was a strong smell and caused me to be concerned.I asked the First Officer if they smelled anything and he said he and described it like brining brakes or cat clutch. I stopped the taxi; set the brakes; and contacted the Flight Attendants to see if they smelled anything and/or saw anything. They said that they smelled the same thing we did but didn't see anything.I then contacted maintenance to see if they had any insight. They said they didn't know what the smell could be and recommended to turn the APU. We turned the APU off and waited to see if the smell dissipated. The smell didn't increase but didn't really dissipate either. I checked with the Flight Attendants to see what they thought. They agreed that it didn't increase but didn't really dissipate.I relayed this info to maintenance on the phone and they said either way we had to return to the gate. So I hung up; had the First Officer contact the station to let them know we were returning to the gate. Given where we were on the ground in ZZZ our only option to taxi back would be to back taxi on Runway XX. However there was a CRJ on approach and due to the airport being un-towered we thought it best to wait until after the CRJ landed. We held short of Runway XX at taxiway A6.While waiting I started to feel a little light headed; nauseous; and some tingling in my fingers and toes. It dawned on me that we could be inhaling carbon monoxide and these were symptoms of carbon monoxide. We donned our O2 masks and I called the Flight Attendants to see how they were feeling. They reported similar symptoms to what I was feeling. After the CRJ landed we back taxied on 10; and then A5 to the gate. However at this point we couldn't hail operations on the radio and could see that they were doing some sort of huddle on our gate spot. We tried several times to get them on the radio and tried getting their attention by flashing lights to no joy. We then assumed they weren't doing anything due to the CRJ parked next to our spot deplaning and passengers walking into the terminal.Eventually; whoever was working the UNICOM frequency relayed what we needed to our station operations. We specifically said that we needed to get the GPU plugged in right away so we get the engines shut off. I was planning on turning the APU back on temporarily to get the engines off without losing power and to allow them to plug in the GPU after which the APU would come off. I chose to do this since we didn't know what the source of the smell was.After maybe 10-15 minutes we finally got waved into the gate and turned on the APU while taxiing in. After stopping; setting brakes; and turning off the engines I again tried to get the ramp to plug in the GPU. At this point we took our O2 masks off and noticed the smell was even worse and my symptoms increased.They either misunderstood or were just being slow at getting the GPU in. I opened the window and told them several times to get it done. I don't know if they were having problems; training; or were taking care of other things but it took about 5 minutes to get the GPU plugged.Once the GPU was plugged in we turned the APU off and had passengers deplane. I contacted maintenance and they informed me that on call maintenance was coming to help resolve the issue. I contacted dispatch to advice of the situation.Maintenance showed up; we informed them what happened and they said that our maintenance wanted to talk to me. I called back and they said that they wanted us to help do engine runs to help isolate the source of the smell/fumes and to fill out a fumes/odor form.I filled out the form with the crew. After that I noticed I was still feeling lightheaded; nauseous; and tingling in my fingers. I decided that helping with engine runs was not a good idea and contacted Medlink to get a medical opinion. After a lengthy conversation I was advised by Medlink that I should not operate the aircraft until getting a medical checkout.I notified Maintenance; Dispatch; and then crew scheduling that I was out due to medical. While waiting for Medlink to call me back to let me know which local area hospital that I could go to get checked out I advised the rest of the crew to call Medlink if they were still feeling symptomatic. The Flight Attendants and the First Officer did. The Flight Attendants got cleared but the First officer did not.After some time getting the hotel and hospital organized we got on the hotel van to the hotel; organized a ride to the hospital; and got our procedures and tests done. We got cleared; we returned to the hotel; reconvened in the morning to determine if we felt OK to work. We agreed that we did and got all additional clearances from Medlink to operate.We should have donned our O2 masks sooner. Since we were on the ground and not in flight it just didn't cross my mind due to everything else that were taking care of. Also looking back shouldn't have turned the APU back on and just had the GPU plugged in before engine shutdown.
EMB-175 Captain reported a 'burning odor' noticed by entire flight crew resulting in a ground gate return; flight cancellation as well as flight crew receiving medical treatment.