III THIRDLY, THE NLRC COMMITTED GRAVE ABUSE OF DISCRETION IN REVERSING THE POEA DECISION ON THE BASIS OF DOCUMENTS WHICH AT BEST ARE NOT CONCLUSIVE AS TO THE CAUSE OF DEATH OF SUBJECT SEAMEN."iv[4] Petitioners claim respondent Commission gravely abused its discretion in admitting private respondent's additional evidence on appeal. Petitioners allege that the additional evidence were "surreptitiously" submitted in violation of petitioner's right to due process. The submission of additional evidence before the respondent Commission is not prohibited by the New Rules of Procedure of the NLRC. After all, rules of evidence prevailing in courts of law or equity are not controlling in labor cases.v[5] The NLRC and labor arbiters are directed to use every and all reasonable means to ascertain the facts in each case speedily and objectively, without regard to technicalities of law and procedure all in the interest of substantial justice.vi[6] In keeping with this directive, it has been held that the NLRC may consider evidence, such as documents and affidavits, submitted by the parties for the first time on appeal.vii[7] The submission of additional evidence on appeal does not prejudice the other party for the latter could submit counter-evidence.viii[8] In the case at bar, the additional evidence was submitted by private respondents before the respondent Commission in their Memorandum on Appeal dated November 8, 1993. The decision of respondent Commission was rendered on April 25, 1994, i.e., six (6) months after the additional documents were submitted. Petitioners had ample opportunity to object and refute the documents. They had the chance to submit counterevidence during this period but they did not do so. It was only when they moved for reconsideration of the decision of respondent Commission that they questioned the admission of these evidence. The essence of due process is simply an opportunity to be heard, or as applied to administrative proceedings, a fair and reasonable opportunity to explain one's side.ix[9] It is also an opportunity to seek a reconsideration of the action or ruling complained of.x[10] It is not the denial of the right to be heard but denial of the opportunity to be heard that constitutes violation of due process of law.xi[11] Procedural matters having been disposed of, the substantive issue in this case is whether respondent Commission gravely erred in finding that the deaths of the two seamen, Eduardo Misada and Enrico Envidiado, did not come as a result of their willful and deliberate act. Part II, Section C, No. 1, Paragraph 1 of the POEA "Standard Employment Contract Governing the Employment of All Filipino Seamen on Board Ocean-Going Vessels"xii[12] provides that: