What type of injection causes grounding for a minimum of 24 hours?

The type of injection that causes grounding for a minimum of 24 hours is associated with Novocaine. This local anesthetic is commonly used in dental procedures and other situations requiring numbing. The grounding period allows aircrew members to recover from the effects of the anesthetic, ensuring that they are fully alert and capable of performing their duties safely before returning to duty.

In contrast, other injections like the flu vaccination, tetanus shot, and COVID-19 vaccine typically do not require a similar grounding period. These vaccinations may result in mild side effects, but they usually do not impair cognitive or physical abilities enough to warrant extended grounding. Thus, Novocaine stands out due to its potential to significantly affect motor and sensory functions immediately post-administration, which is why a grounding period is stipulated.