Woo explains that the survey is modelled on a two-year health investigation that followed a 1987 leak at an oil refinery in Texas, when 18 tonnes of HF were released (H. H. Dayal et al. Ann. Epidemiol. 2, 213–230; 1992). In contrast to the accident at Gumi, however, the authorities there acted quickly to contain the leak. Within seven minutes of the release, water was used to contain and hydrate the escaping gas; within 20 minutes, a 0.8-kilometre evacuation zone was established.