Authorities initially believed a local sulphur-producing factory was to blame for the odour, but said the probe was ongoing and inconclusive.
Industrial Estate Authority of Thailand (IEAT) governor Verapong Chaiperm confirmed yesterday that investigators had ascertained that a tapioca flour factory outside the industrial estate was in fact the cause of the strong smell, not the sulphur plant.
IEAT confirmed that the odour is no longer affecting residents and the situation has returned to normal.
Natthapol Natthasomboon, director-general of the Industrial Works Department, said officers will order the suspension of the factory's operations.
An inspection of the factory's premises will also be carried out.
The strong smell of gas drove about 300 residents of Ban Chang district out of their homes, said Insee Kerdmanee, Ban Chang district office chief.
The residents took shelter at a nearby sports stadium at about 8pm.
They remained there until 4am yesterday when heavy rain began to fall, forcing them to return to their homes.
Two Ban Chang residents, La-iad Nammaungsak, 59, and Samai Suriyawong, 83, were rushed to hospital after suffering dizziness, nausea, vomiting and breathing difficulties.
Map Ta Phut Industrial Estate's Environmental Monitoring and Control Centre (EMCC) yesterday sent a team to affected areas to investigate the incident.
The EMCC also sought cooperation from factories on the industrial estate to locate the source of the smell.
EMCC staff detected a smell similar to burning matches or gun powder which appeared to come from the Ban Noen Kraprok community.
Despite the tapioca flour factory being identified as the cause of the odour, EMCC workers received several complaints from residents about the sulphur-producing factory nearby.