Your friend is lucky that he did`nt have much damage after consuming harpic which contains acid though mild and many other chemicals. He could have developed hyper reactive airways after inhaling the fumes or some of it may have gone down his airways. He may go in for chest CT to asses the damage to the lung parenchyma and a PFT. The risk is if he has any damage to lungs he may develop broncheactasis and he may get repeated chest infections.He may develop hyper reactive airways and have asthma
may develop ILD. If he has no symptoms at present.