In Empire of the Sun, what techniques are used to show the fragility of life?

One technique is symbolism. As Jim explores his empty family home, he sees the drained swimming pool, which he has never seen empty. It seems strange to him, a thing explicitly created by human hands for human enjoyment, and without its water it serves no purpose. Life created it, but without that life, it is empty and meaningless.

There was something sinister about a drained swimming pool... it reminded him of the concrete bunkers in Tsingtao, and the bloody handprints of the maddened German gunners... perhaps murder was about to be committed in all the swimming pools of Shanghai, and their walls were tiled so that the blood could be washed away.
(Ballard, Empire of the Sun, Google Books)

The comparison to the concrete bunkers adds another symbolism to the empty pool; it was created for the enjoyment of life, but now it may serve as a place for death. If so, it will have transcended its purpose and become a place where life ends instead of where life thrives; it can be changed so easily because it is a construct, not a living thing. Without humans, the empty pool is only a void, a place waiting to be filled with something. Human life informs the pool, whether thriving or ending inside it; the empty pool will remain long after humans vanish entirely.