Yes, there is a safety glass vial under the burner, or rather the Rheem technician asked me over the phone if I saw broken glass. If it blows your water heater is shut down until Rheem mails you a replacement. They do not let supply houses hold replacements for this situation. Even if the vial blows 6 months after install the customer will still blame you for the problem. I'm not going to get an irate customer calling me a year later claiming my water heater failed. Nor will I wait for them to mail me a replacement which would cost me yet another trip. I simply refuse to buy Rheem.
The 1st and only time that happened to me I dumped the water heater at the supply house and told them no more water heater purchases there until they go back to Bradford White. But we only buy about 10 heaters a month. No Rheem, no way.