Thermally induced biological effects should be preventable by avoiding a local tissue temperature increase exceeding:

• A. 1 degree C
• B. None; thermal effects have no threshold
• C. 4 degrees C
• D. 10 degrees C

Answer: (A)

The main idea is that tissue can tolerate only a small amount of temperature rise before biological effects begin to appear, so keeping the local temperature increase very low helps prevent injury. A small rise, around 1°C, is used as a conservative safety limit because it minimizes the risk of disrupting proteins and membranes and avoids stressing cells and blood flow. If the temperature climbs by 4°C or 10°C, the likelihood of irreversible damage and thermal injury increases, so those higher thresholds are not considered safe defaults. Saying there’s no threshold ignores the well-established idea that tissue damage can occur once a certain temperature rise is reached. So, avoiding a local temperature increase exceeding about 1°C is the prudent guideline to prevent thermally induced effects.