Well, I don't think it is a bad idea to wash your hands after masturbation. Not for the reason you mention but just because it is good hygiene. Touch genital area, wash hands. Good practice to be in. However, with regards to pregnancy, you can not get pregnant from surface sperm. A penis must go into the vagina for pregnancy to occur. If you have obsessive thoughts and compulsive rituals, it would be wise to speak to a doctor about that as anxiety and OCD can make for a difficult life. good luck
Yes surface sperms are dead sperms. For conception, you need live cells and which travels with speed. As they are not in medium, they cannot travel , so need not bother about any accident. You are safe.
You might have to check with the doctor about OCD i have OCD myself and everytime i touch a door, toilet handle, bath, ATM, shopping cart or even a person i wash my hands because i'm scared of germs.