Heart Disease; and, that the employees compensation law is social legislation and, hence, it should be interpreted liberally in favor of the worker; and to substantiate these allegations, he submitted the Certifications issued by the Department of Health, to the effect  that the Records Management and Archives Office, including all (Medical Services) Divisions,   is found to be exposed to chemical hazard, in performing its actual duties and responsibilities; [ 6 ]  that all the employees of the Records Management and Archives Office at T.M. Kalaw St., Manila are at risk of developing respiratory illnesses due to their direct/indirect exposure to dust, biological hazards (such as fungi, yeast, etc.) producing noxious odor emanating from ancient files/vends which are preserved; that they are exposed to chemicals usually used as preservatives; [ 7 ]  and, that the employees of the Records Management and Archives Office, Region XI, Davao City are at risk/danger to their health and safety due to the following findings/observations:   1. Risk from exposure to dangerous, noxious odors/toxic chemicals/ gas in the conduct of processing, pressuring and fumigation of old files and records; and,   2. Risk from exposure to biological hazards and other substances like dust, molds, ticks, silver fish and other insect and vectors located in the ill-ventilated and cramped workplace. [ 8 ]     A review of the findings of facts of the CA and the agencies  a quo  fails to show that the respondent discharged his burden of proof, under the measure of substantial evidence, that his working conditions increased the risk of contracting Rheumatic Heart Disease. In particular, the records show no medical information establishing the etiology of Rheumatic Heart Disease that would enable this Court to evaluate whether there is causal relation between the respondents employment and his illness.