Could ingesting small amount of paint thinner be deadly or poisonous? what immediate actions should one take?

Possible ER: Even small amounts of paint thinners (hydrocarbons) can cause significant problems most commonly lung problems. Symptoms of pneumonia can occur 4 to 6 hours after ingestion. It is not recommending to induce vomiting as that increases the risk of lung problems. I do not know what a small quantity truly means. If it was essentially a drop or two you are probably safe. If it was more seek ER advice