Sound intensity is measured in units of measurement named after the inventor of

Sound intensity is measured in decibels (dB).
The human threshold for hearing is 0 decibels.
Sound levels in a quiet library are about 30 decibels, levels in a tool shop or near truck traffic are about 90 decibels, at a rock concert near the speakers it is about 120 decibels, and near loud noises like a gunshot or jet engine it is about 140 decibels.
Brief exposure to loud noises at 120 to 140 dB or above can cause immediate damage to hair cells, although sustained exposure to sounds at 90 dB can also cause damage.
Hair cells are fragile and hearing loss can result when many hair cells are damaged.