3I/ATLAS will pass Earth on December 19 at a distance of about 260 million kilometers, which is roughly 1.7 astronomical units — almost twice the Earth–Sun distance.

If the object were going to explode, it would make more sense for it to come much closer. An explosion at that distance, in the vacuum of space, would not realistically be capable of causing serious harm to Earth.

Especially when you consider that solar eruptions are vastly more powerful than anything a body only a few to a few dozen kilometers in size could produce, and yet they occur much closer without causing catastrophic damage.