How long must exposure be to develop pulmonary oxygen toxicity?

Developing pulmonary oxygen toxicity is primarily associated with prolonged exposure to elevated partial pressures of oxygen. When exposed to high concentrations of oxygen, especially beyond normal atmospheric levels, the lungs can begin to suffer from oxidative stress. This effect happens because oxygen at high levels leads to the production of reactive oxygen species, which can damage cellular structures and lead to inflammation.

Long exposure is required for the toxicity to manifest because the body can tolerate moderate levels of oxygen for shorter durations without significant adverse effects. Acute exposure, while potentially harmful, may not provide enough time for the cumulative effects to lead to toxicity. Therefore, it is the extended duration of exposure that significantly increases the risk of pulmonary oxygen toxicity, thereby making long exposure the correct answer.