Final answer:
The FDA does not have a specific decibel (dB) limit for MRI, but it is recommended not to exceed 85 dB for 8-hour periods without hearing protection. MRI scanners usually operate at higher levels, thus hearing protection is typically used.
Step-by-step explanation:
The FDA has not specified a decibel (dB) limit specifically for MRI machines. However, government agencies and health organizations commonly suggest that exposure to sound levels should not exceed 85 dB without hearing protection for periods longer than 8 hours. MRI machines often operate at levels higher than this, which is why patients and technicians are usually provided with hearing protection during MRI scans. For reference, 85 dB is about the sound intensity of a busy urban street, while levels around 100 dB can be compared to the sound of a jet plane taking off, which is a brief, rather than continuous, exposure.