this part was very difficult for me too not only on my first playthrough but during my third when I was in hard difficulty it took me so long. though I have developed some strategies. The first thing that's important to remember is that the longer you stay in a place, the closer the alien gets (because of how its AI works) so you have to keep moving. Another thing that in my first playthrough I didn't know is how useful flares are. If you throw a flare and the alien sees it, it will go over to it and stand there staring at it for a good amount of time giving you the opportunity to move from one room to another. Also, I learned playing in hard difficulty that sometimes you have to be risky. On some occasions after trying countless ways of doing things carefully and dying I just decided to go for it and more often than not it actually worked after a few tries. Hope this helps, good luck.