hi,in pulmonary TB,the pathology is such that the bacillus cause inflammatory changes in bronchioles or alveoli.Also ,they(bacilli) are ingested by the leukocytes & later forming a mass called 'tuberculous follicle'.After 'caseation'this is coughed up leaving a cavity behind.The calcified lesion is the main source of infection.
The danger with chest physio is mainly during the 'active stage'(or acute stage,or rest stage)as there can be spread of disease to other areas of lung.Another reason is cross infection if no proper precaution is taken ,yet another reason is haemoptysis.
Not all chest physio is contraindicated... there are safer ways too 1)put patient in required posturural drainage positions only.2)give mild vibrations to desired lobe & practice "autogenic drainage".....
hope this will help u