Rodney breathed experimentally through his nose. Still difficult but a little better. The throbbing in his head had subsided to a bearable level too, maybe he could actually pull this off. Wouldn't be the first time he'd beaten impossible odds in the name of science. In fact it was becoming a habit, must be Sheppard's influence. Hopefully it wouldn't have the same effect on his hair.

The transporter stopped, the doors opening with a slight hiss. It really was like being on Startrek. He made his way to the massive chamber where the O2 filters hummed reassuringly away. The filters extracted air from outside the city, passed it through conduits coated with a variety of chemicals designed to extract any toxins, and then directed it around Atlantis. Though there were plenty of doors and windows to the outside, these were insufficient to supply the entire city with oxygen especially as some of it was still underwater. The filters provided life support to about 80 of the city. Hence they were very, very, important.

The soldiers 'guarding' the environmental controls looked up as he came in. "Hey Doc." one of them drawled, a Lieutenant Harris if he remembered correctly. Grunting absently, he headed straight for the controls, opening the necessary programmes to run a diagnostic.

"So…what's the weather forecast today?" The other one…Captain something or other inquired. Would these people never comprehend the importance of silence when a genius was at work?

"What?"

"You know, the weather? Sun, rain, clouds, we've been on duty since 0100."

"Oh…I didn't look."

"You didn't look?"

"I had more important things to do than check out the view Captain." He coughed again, trying to focus on the blurry sequence of numbers in front of him. Damn his throat was sore, and being forced to make idle conversation wasn't helping.

"You alright McKay."

"Yes fine, thank you."

"Only I'd hate you to spend that cough through Atlantis. The indigestion we get from the rations is bad enough."

"The air in here is dry Lieutenant, not that you'd notice."

"What's that mean to mean?"

"It's blocked."

"What?"

"Not you...just…look at this." He gestured for the guards to see the display. "The conduit to the mess hall is blocked. Nothing is getting through."

"Wouldn't whoever was guarding the bay have noticed?"

"Not necessarily, there is a lot redundancy built into all the ancient systems. The oxygen might be a little lower than usual but not enough to be noticeable when there are other conduits feeding into areas close by."

"So what's the problem?"

"The problem is that these filters are designed to go one way, there are valves in place to prevent the air going backwards. So instead of the air being released into Atlantis, there's a build up in the conduit."

"How big a build up?"

"Big."

"But it's just of air right? Harmless oxygen, nitrogen, carbon dioxide?"

"The initial build up might be, but see this valve here? It's made of something akin to rubber on earth. Now this is swollen and has blocked off this valve. Which is unfortunately carrying something a lot more harmful."

"Chlorine?"

"You got it. Chlorine is directed to the water tanks, but the build up in the air conduit is so severe that a significant amount of chlorine has been trapped too. All the conduits run alongside each other."

"It's going to blow?"

"In less than fifteen minutes. And when that happens, chlorine gas is going to be fed right into Atlantis. If we don't stop it, it'll kill anyone within a mile's radius of that section."

"What can we do?" All humour was gone from their faces now. Good, he needed their help.

"I need to get down to the conduits where the blockage is. They run along the top of a larger passage which carries water to those sections. I need you to contact Dr Zelenka and tell him to shut of water to passage 109A. With the flow turned off I should be able to crawl along the passage, locate the blockage and vent the excess gas it before both it and the air conduit rupture. The passage way will need to be sealed off until I can reroute the valve." He took a deep breath "And all of this needs to happen in the nest twelve and a half minutes!"

"Acknowledged." The Captain picked his radio up from the console, "But Doc, if you're venting the gas into the passageway how will you avoid getting poisoned?" McKay was already halfway out the door,

"Oxygen Captain. Oxygen."

By the time McKay reaching the hatch to the water tunnel, the flow had already been turned off. "Thank you Zelenka." Rodney breathed, gingerly opening the narrow entrance. The passage was dark, damp, and only just big enough for someone to squeeze into. He turn on his torch, took a deep, deep breath, and climbed in.

Inside, the passage seemed even smaller. "I am not in a small, dark tunnel which could fill up with water at anytime. I am not in a small dark tunnel that could- oh dammit." He pulled the navigation device out of his pocket. "Right, only ten metres left. Hardly anything, there are rooms bigger than that. Ten metres, just a little-At-choo! A little further. Ow! What-you'd think they'd make these passage ways bigger! Ow my head! As though I haven't got enough problems. I wonder how much air is in here? Plenty! Just because the door is shut and this is a really really narrow passageway that is usually full of water…ah! Here it is!" He looked up, half a dozen rubbery black tubes ran over his head. One was visibly swollen and blocked another which was even more swollen. "Right. So all I need to do is vent the gas here, so it'll release the valve in the chlorine conduit and we won't all die. Easy." He coughed. "Easy."

Five minutes later he was forced to admit it wasn't so easy. It looked like the valve in the air conduit was actually stuck, completely closing off the of the tube. And to make it worse it seemed like the pressure of the air conduit pressing against it had permanently disfigured the shape of the tube carrying the chlorine. He needed to completely replace that section of tubing. But to do that…

"Rodney?" the slightly accented voice echoed through the tunnel. "Have you located the problem?"

"Radek, yeah, it isn't looking so good. I have to replace one of the conduits."

"Which one?"

"Which one do you think? The poisonous one of course. You think I'd ever actually get it easy?"

"Rodney you should not be doing this! You are not well!"

"I know, I know, but we don't have time to argue about it now. Now have you cut off the gas supply to the this passage?"

"Most of it. However we still don't understand all of the engineering behind the ancient systems and we-"

"Just tell me." He could almost hear Zelenka sigh.

"We cannot stop the chlorine gas." Rodney sat back disbelievingly.

"Great. Just great."

Rodney closed the entrance to the hatch again, trying to forget the sight of Radek's concerned expression. He might not understand Czech but he could guess at the meaning of some of Radek's words. Still, too late to turn back now. He crawled back to the conduits.

With the air supply shut off, all he needed to do was puncture the air conduit to release the pressure built up. He could repair it later. The still-flowing chlorine would be harder. He couldn't block it off or there would just be another build up of gas that could rupture who knows where. He had to let it filter out into this passage. Both ends of the tunnel had been sealed off, and surrounded rooms evacuated. The only people at risk were the scientists outside the tunnel, anxiously monitoring his progress, and him. He had to stop being so heroic, it wasn't good for his health. He coughed miserably and punctured the air conduit.

He was rewarded by the hiss of air escaping. The valve began to deflate. Step one complete. Now for the tricky part. He pulled the goggles and oxygen mask from the pack Radek had handed him whilst talking into his headset.

"I've deflated the first conduit. About to start repairs on the chlorine pipe now."

"Acknowledged," a pause, "Good luck Rodney."

"You had to say it didn't you?" he paused too, "Thanks."

Silence, he fitted his goggles, put on the oxygen tank and mask, and got out his knife. Then taking a deep breath of the precious air, he slit the tube open.

It wasn't that he was mortally terrified of sitting in a tunnel full of poisonous gas. It was just that…okay he was mortally terrified. He didn't want to die, was that so awful? Even Sheppard couldn't want to die. He was just better at hiding it.

"Are you okay Rodney?" Radek's voice filtered through, he frowned irritably, "I'm fine, why wouldn't I be, it isn't like chlorine is poisonous, oh wait! It is!"

"I just mean...you breathe very fast."

"Well…I'm claustrophobic. And this is a very small, very enclosed space. So If you don't mind, I'd like to hurry up and finish so I can get out of here!"

Silence. "Okay Rodney. We'll see you soon."

"Fine. Don't call me, I'll call you," and he took his headset off.

Almost done. He just had to finish sealing the other end of the new tube. Then he could go back outside having proved himself once again to be the smartest man in Atlantis. Well, at least a good engineer. He'd have saved the day anyway. He coughed awkwardly into his mask. And again. God what was wrong, his throat felt like it was closing over. He pulled off his tank to check the air supply and stopped, staring in horror. It looked like he'd been careless putting his knife down. It had cut a small hole in the tube leading to his mask. Small? The tube was almost cut in half! Air was flowing straight out, and chlorine straight in. Dammit! He turned back to the chlorine conduit, he had to finish this, otherwise the gas would just be left flowing and could get so strong it would be lethal for anyone to even try and finish. He could do this…he ignored the mask and put his mouth to the puncture in the air conduit. Sweet, sweet oxygen! He took a deep shuddering breath. He had to.

He was done, which was good as so was the leftover air in the piping. He just had to crawl the ten metres back to the hatch. Easy, he could do it. He took a last halting breath, ignoring the burning in his chest and throat and began.

See, he could make it. A little further. God, his lungs were going to explode! He had to breathe! Surely the air was cleaner up here! He gulped in air, only to collapse coughing to the floor of the tunnel. Wrong. He was going to die. Only a couple of metres from safety. His headset was still down there, he shouldn't have taken it off. Stupid McKay, stupid. He was always stupid. Sorry Elizabeth, sorry Sheppard, didn't mean it to go down like this. Sorry Radek. He was so dizzy, he couldn't breathe-

And everything burst in an explosion of white light.

Hey guys! Isn't it dramatic? Poor old Rodney :) Whatever will happen to him next. Provided I don't kill him off of course...though that would take the fun out of whumping him. And how will he avoid Carson now?

Please spend a few seconds to leave me a review? I eat, sleep, and breathe opinions ;)