Experimental evidence and pathogenesis. Acute massive exposure to wood smoke, as in forest fires, can be rapidly lethal. Besides asphyxia and carbon monoxide intoxication there may be severe damage to the respiratory epithelium , with airway and pulmonary oedema. Lesser degrees of wood smoke exposure in guinea pigs produces bronchoconstriction and increases the response to subsequent exposure (65). After exposure to wood smoke for 3 hours a day for 3 months, guinea-pigs developed mild emphysema (66). Rats exposed intermittently to wood smoke for 75 minutes daily for 15 days had mononuclear bronchiolitis and mild emphysema; these conditions became more severe following exposure for 30 and 45 days (67). A fibrotic lung reaction simulating silicosis has been produced experimentally in animals exposed to wood smoke (68).