Simplify the following text for a Grade 5 native English-speaking person.
Original: This gas chamber operated from 1941 to 1942 , during which time some 60,000 people were killed therein ; it was then converted into an air-raid shelter for the use of the SS .
Simplified: They used this from 1941 to 1942 , and killed about 60,000 people by sending them to the gas chamber . After this , they made this as an air-raid shelter for the use of SS .