are generally safe. However, if a soda bottle ruptures, not only can it have a loud explosion, but anything in near proximity could be severely damaged.
Above is an example of a HEAVY DUTY cotton shirt blown to bits. While bench testing a launcher, I observed that while pressurizing, and filling the soda bottle with air, the pressure gauge needle was not rising. THIS IS AN INDICATION OF A WEAK BOTTLE! As a precaution to contain flying debris and water, I grabbed this shirt and threw it over the bottle. Even though I ceased filling the bottle, it continued to swell and exploded. I was very surprised to see the damage to my favorite winter shirt.
Extra caution should be made to PREVENT anything from being in DIRECT CONTACT with a pressurized soda bottle!!!!
I display this shirt in my shop as a reminder to always wear safety glasses and ear protection, and to maintain a SAFE distance from pressurized containers. I install 12 foot long hoses on the Bigfoot Water Rocket Launchers to put a safer distance between rockets and people.