This amendment makes revisions to a final rule published in the Federal Register under Docket Nos. HM-181, HM-181A, HM-181B, HM-181C, HM-181D and HM-204 (55 FR 52402, December 21, 1990). That final rule comprehensively revised the Hazardous Materials Regulations (HMR; 49 CFR parts 171-180) with respect to hazard communication, classification and packaging requirements. The changes were based on the United Nations Recommendations on the Transport of Dangerous Goods (UN Recommendations) and RSPA's own initiative. The revisions contained in this document are in response to petitions for reconsideration addressing the transitional provisions contained in the final rule. This amendment also extends the effective date for certain quantities of infectious substances and incorporates all rulemaking actions issued under Docket HM-142A (56 FR 197, January 3, 1991, and 56 FR 7312, February 22, 1991) into Docket HM-181. RSPA will respond to other petitions for reconsideration in a forthcoming corrections document. The revision of the transition period will allow adequate time for persons subject to the HMR to evaluate domestic products for changes in classification, descriptions on shipping papers, product marking, labeling and vehicle placarding, to conduct package testing, and to provide sufficient time for the retraining of shipper, carrier, enforcement, and emergency response personnel in the new requirements.