PART 51—ENVIRONMENTAL CRITERIA AND STANDARDS Authority: 42 U.S.C. 3535(d), unless otherwise noted. Source: 44 FR 40861, July 12, 1979, unless otherwise noted. Subpart A—General Provisions § 51.1 Purpose. The Department of Housing and Urban Development is providing program Assistant Secretaries and administrators and field offices with environmental standards, criteria and guidelines for determining project acceptability and necessary mitigating measures to insure that activities assisted by the Department achieve the goal of a suitable living environment. § 51.2 Authority. This part implements the Department's responsibilities under: The National Housing Act (12 U.S.C. 1701 et seq. [61 FR 13333, Mar. 26, 1996] § 51.3 Responsibilities. The Assistant Secretary for Community Planning and Development is responsible for administering HUD's environmental criteria and standards as set forth in this part. The Assistant Secretary for Community Planning and Development may be assisted by HUD officials in implementing the responsibilities established by this part. [61 FR 13333, Mar. 26, 1996, as amended at 91 FR 35626, June 12, 2026] § 51.4 Program coverage. Environmental standards shall apply to all HUD actions except where special provisions and exemptions are contained in each subpart. Subpart B—Noise Abatement and Control § 51.100 Purpose and authority. (a) It is the purpose of this subpart B to: (1) Call attention to the threat of noise pollution; (2) Encourage the control of noise at its source in cooperation with other Federal departments and agencies; (3) Encourage land use patterns for housing and other noise sensitive urban needs that will provide a suitable separation between them and major noise sources; (4) Generally prohibit HUD support for new construction of noise sensitive uses on sites having unacceptable noise exposure; (5) Provide policy on the use of structural and other noise attenuation measures where needed; and (6) Provide policy to guide implementation of various HUD programs. (b) Authority. et seq. Compatible Land Uses at Federal Airfields. [44 FR 40861, July 12, 1979, as amended at 61 FR 13333, Mar. 26, 1996] § 51.101 General policy. (a) It is HUD's general policy to provide minimum national standards applicable to HUD programs to protect citizens against excessive noise in their communities and places of residence. (1) Planning assistance. (i) Particular emphasis shall be placed on the importance of compatible land use planning in relation to airports, highways and other sources of high noise. (ii) Applicants shall take into consideration HUD environmental standards impacting the use of land. (2) Activities subject to 24 CFR part 58. (ii) Where activities are planned in a noisy area, and HUD assistance is contemplated later for housing and/or other noise sensitive activities, the responsible entity risks denial of the HUD assistance unless the HUD standards are met. (3) HUD support for new construction. (4) HUD support for existing construction. (5) HUD support of modernization and rehabilitation. (6) Research, guidance and publications. (7) Construction equipment, building equipment and appliances. (8) Exterior noise goals. (9) Interior noise goals. (10) Acoustical privacy in multifamily buildings. [44 FR 40861, July 12, 1979, as amended at 50 FR 9268, Mar. 7, 1985; 61 FR 13333, Mar. 26, 1996] § 51.102 Responsibilities. (a) Notice to applicants. (1) Determine the suitability of the acoustical environment of proposed projects; (2) Notify applicants of any adverse or questionable situations; and (3) Assure that prospective applicants are apprised of the standards contained herein so that future site choices will be consistent with these standards. (b) Interdepartmental coordination. [44 FR 40861, July 12, 1979, as amended at 54 FR 39525, Sept. 27, 1989; 61 FR 13333, Mar. 26, 1996; 91 FR 35626, June 12, 2026] § 51.103 Criteria and standards. These standards apply to all programs as indicated in § 51.101. (a) Measure of external noise environments. dn (b) Loud impulsive sounds. Cdn (c) Exterior standards. (2) The noise environment inside a building is considered acceptable if: (i) The noise environment external to the building complies with these standards, and (ii) the building is constructed in a manner common to the area or, if of uncommon construction, has at least the equivalent noise attenuation characteristics. Site Acceptability Standards Day-night average sound level (in decibels) Special approvals and requirements Acceptable Not exceeding 65 dB(1) None. Normally Unacceptable Above 65 dB but not exceeding 75 dB Special Approvals (2) Environmental Review (3). Attenuation (4). Unacceptable Above 75 dB Special Approvals (2). Environmental Review (3). Attenuation (5). Notes: (1) Acceptable threshold may be shifted to 70 dB in special circumstances pursuant to § 51.105(a). (2) See § 51.104(b) for requirements. (3) See § 51.104(b) for requirements. (4) 5 dB additional attenuation required for sites above 65 dB but not exceeding 70 dB and 10 dB additional attenuation required for sites above 70 dB but not exceeding 75 dB. (See § 51.104(a).) (5) Attenuation measures to be submitted to the Program Assistant Secretary or their designee for approval on a case-by-case basis. [44 FR 40861, July 12, 1979, as amended at 49 FR 12214, Mar. 29, 1984; 91 FR 35626, June 12, 2026] § 51.104 Special requirements. (a)(1) Noise attenuation. (2) Normally unacceptable noise zones and unacceptable noise zones. (b) Environmental review requirements. (1) Normally unacceptable noise zone. (ii) When an EIS is required, the concurrence of the Program Assistant Secretary is also required before a project can be approved. For the purposes of this paragraph, an area will be considered as largely undeveloped unless the area within a 2-mile radius of the project boundary is more than 50 percent developed for urban uses and infrastructure (particularly water and sewers) is available and has capacity to serve the project. (iii) All other projects in the Normally Unacceptable zone require a Special Environmental Clearance, except where an EIS is required for other reasons pursuant to HUD environmental policies. (2) Unacceptable noise zone. [44 FR 40861, July 12, 1979, as amended at 61 FR 13333, Mar. 26, 1996; 91 FR 35626, June 12, 2026; 91 FR 53718, Aug. 20, 2026] § 51.105 Exceptions. (a) Flexibility for non-acoustic benefits. dn (1) The project does not require an Environmental Impact Statement under provisions of § 51.104(b)(1) and noise is the only environmental issue. (2) The project has received a Special Environmental Clearance and has received the concurrence of the Environmental Clearance Officer. (3) The project meets other program goals to provide housing in proximity to employment, public facilities and transportation. (4) The project is in conformance with local goals and maintains the character of the neighborhood. (5) The project sponsor has set forth reasons, acceptable to HUD, as to why the noise attenuation measures that would normally be required for new construction in the L dn dn (6) Other sites which are not exposed to noise above L dn The above factors shall be documented and made part of the project file. [44 FR 40861, July 12, 1979, as amended at 61 FR 13334, Mar. 26, 1996] § 51.106 Implementation. (a) Use of available data. (1) Sites in the vicinity of airports. DNL ≉ NEF + 35 DNL ≉ CNEL (2) Sites in the vicinity of highways. 10 eq 10 eq DNL ≉ L 10 DNL ≉ L eq Where the auto/truck mix and time of day relationships as stated in this section do not exist, the HUD Noise Assessment Guidelines or other noise analysis shall be used. (3) Sites in the vicinity of installations producing loud impulsive sounds. Cdn Cdn (4) Use of areawide acoustical data. (b) Site assessments. (c) Variations in site noise levels. (d) Noise measurements. (e) Projections of noise exposure. (f) Reduction of site noise by use of berms and/or barriers. [44 FR 40861, July 12, 1979, as amended at 61 FR 13334, Mar. 26, 1996; 91 FR 35626, June 12, 2026] Appendix I to Subpart B of Part 51—Definition of Acoustical Quantities 1. Sound Level. 2. Average Sound Level. Day-night average sound level, abbreviated as DNL, and symbolized mathematically as L dn Time t is in seconds, so the limits shown in hours and minutes are actually interpreted in seconds. L A 3. Loud Impulsive Sounds. A loud impulsive sound is defined for the purpose of this regulation as one for which: (i) The sound is definable as a discrete event wherein the sound level increases to a maximum and then decreases in a total time interval of approximately one second or less to the ambient background level that exists without the sound; and (ii) The maximum sound level (obtained with slow averaging time and A-weighting of a Type 1 sound level meter whose characteristics comply with ANSI S1.4-1971) exceeds the sound level prior to the onset of the event by at least 6 decibels; and (iii) The maximum sound level obtained with fast averaging time of a sound level meter exceeds the maximum value obtained with slow averaging time by at least 4 decibels. [44 FR 40861, July 12, 1979; 49 FR 10253, Mar. 20, 1984; 49 FR 12214, Mar. 29, 1984] Subpart C—Siting of HUD-Assisted Projects Near Hazardous Operations Handling Conventional Fuels or Chemicals of an Explosive or Flammable Nature Authority: 42 U.S.C. 3535(d). Source: 49 FR 5103, Feb. 10, 1984, unless otherwise noted. § 51.200 Purpose. The purpose of this subpart C is to: (a) Establish safety standards which can be used as a basis for calculating acceptable separation distances (ASD) for HUD-assisted projects from specific, stationary, hazardous operations which store, handle, or process hazardous substances; (b) Alert those responsible for the siting of HUD-assisted projects to the inherent potential dangers when such projects are located in the vicinity of such hazardous operations; (c) Provide guidance for identifying those hazardous operations which are most prevalent; (d) Provide the technical guidance required to evaluate the degree of danger anticipated from explosion and thermal radiation (fire); and (e) Provide technical guidance required to determine acceptable separation distances from such hazards. [49 FR 5103, Feb. 10, 1984, as amended at 61 FR 13334, Mar. 26, 1996] § 51.201 Definitions. The terms Department Secretary Acceptable separation distance (ASD) Blast overpressure— Danger zone— Hazard (1) Pipelines for the transmission of hazardous substances, if such pipelines are located underground, or comply with applicable Federal, State and local safety standards; (2) Containers with a capacity of 100 gallons or less when they contain common liquid industrial fuels, such as gasoline, fuel oil, kerosene, and crude oil, since they generally would pose no danger in terms of thermal radiation or blast overpressure to a project; (3) Facilities that are shielded from a proposed HUD-assisted project by the topography, because these topographic features effectively provide a mitigating measure already in place; (4) All underground containers; and (5) Containers used to hold liquefied petroleum gas with a volumetric capacity not to exceed 1,000 gallons water capacity, if they comply with National Fire Protection Association (NFPA) 58. NFPA 58, Liquefied Petroleum Gas Code, 2017 Edition, copyright 2016 is incorporated by reference into this section with the approval of the Director of the Federal Register, under 5 U.S.C. 552(a) and 1 CFR part 51. All approved material is available for inspection at HUD's Office of Environment and Energy, 202-402-5226, and is available from National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02169, telephone number 800-344-3555, fax number 800-593-6372, www.nfpa.org email [email protected] www.archives.gov/federal-register/cfr/ibr-locations.html Hazardous substances HUD-assisted project— Thermal radiation level— 2 [49 FR 5103, Feb. 10, 1984, as amended at 61 FR 5204, Feb. 9, 1996; 61 FR 13334, Mar. 26, 1996; 85 FR 4228, Jan. 24, 2020] § 51.202 Approval of HUD-assisted projects. (a) The Department will not approve an application for assistance for a proposed project located at less than the acceptable separation distance from a hazard, as defined in § 51.201, unless appropriate mitigating measures, as defined in § 51.205, are implemented, or unless mitigating measures are already in place. (b) In the case of all applications for proposed HUD-assisted projects, the Department shall evaluate projected development plans in the vicinity of these projects to determine whether there are plans to install a hazardous operation in close proximity to the proposed project. If the evaluation shows that such a plan exists, the Department shall not approve assistance for the project unless the Department obtains satisfactory assurances that adequate mitigating measures will be taken when the hazardous operation is installed. [49 FR 5103, Feb. 10, 1984, as amended at 61 FR 13334, Mar. 26, 1996] § 51.203 Safety standards. The following standards shall be used in determining the acceptable separation distance of a proposed HUD-assisted project from a hazard: (a) Thermal Radiation Safety Standard. (1) The allowable thermal radiation flux level at the building shall not exceed 10,000 BTU/sq. ft. per hr.; (2) The allowable thermal radiation flux level for outdoor, unprotected facilities or areas of congregation shall not exceed 450 BTU/sq. ft. per hour. (b) Blast Overpressure Safety Standard. (c) If a hazardous substance constitutes both a thermal radiation and blast overpressure hazard, the ASD for each hazard shall be calculated, and the larger of the two ASDs shall be used to determine compliance with this subpart. (d) Background information on the standards and the logarithmic thermal radiation and blast overpressure charts that provide assistance in determining acceptable separation distances are contained in appendix II to this subpart C. [49 FR 5103, Feb. 10, 1984, as amended at 61 FR 13334, Mar. 26, 1996] § 51.204 HUD-assisted hazardous facilities. In reviewing applications for proposed HUD-assisted projects involving the installation of hazardous facilities, the Department shall ensure that such hazardous facilities are located at an acceptable separation distance from residences and from any other facility or area where people may congregate or be present. The mitigating measures listed in § 51.205 may be taken into account in determining compliance with this section. § 51.205 Mitigating measures. Application of the standards for determining an Acceptable Separation Distance (ASD) for a HUD-assisted project from a potential hazard of an explosion or fire prone nature is predicated on level topography with no intervening object(s) between the hazard and the project. Application of the standards can be eliminated or modified if: (a) The nature of the topography shields the proposed project from the hazard. (b) An existing permanent fire resistant structure of adequate size and strength will shield the proposed project from the hazard. (c) A barrier is constructed surrounding the hazard, at the site of the project, or in between the potential hazard and the proposed project. (d) The structure and outdoor areas used by people are designed to withstand blast overpressure and thermal radiation anticipated from the potential hazard (e.g., the project is of masonry and steel or reinforced concrete and steel construction). § 51.206 Implementation. This subpart C shall be implemented for each proposed HUD-assisted project by the HUD approving official or responsible entity responsible for review of the project. The implementation procedure will be part of the environmental review process in accordance with the procedures set forth in 24 CFR parts 50 and 58. [61 FR 13334, Mar. 26, 1996] § 51.207 Special circumstances. The Secretary or the Secretary's designee may, on a case-by-case basis, when circumstances warrant, require the application of this subpart C with respect to a substance not listed in appendix I to this subpart C that would create thermal or overpressure effect in excess of that listed in § 51.203. [61 FR 13334, Mar. 26, 1996] § 51.208 Reservation of administrative and legal rights. Publication of these standards does not constitute a waiver of any right: (a) Of HUD to disapprove a project proposal if the siting is too close to a potential hazard not covered by this subpart, and (b) of HUD or any person or other entity to seek to abate or to collect damages occasioned by a nuisance, whether or not covered by the subpart. Appendix I to Subpart C of Part 51—Specific Hazardous Substances The following is a list of specific petroleum products and chemicals defined to be hazardous substances under § 51.201. Hazardous Liquids Acetic Acid Acetic Anhydride Acetone Acrylonitrile Amyl Acetate Amyl Alcohol Benzene Butyl Acetate Butyl Acrylate Butyl Alcohol Carbon Bisulfide Carbon Disulfide Cellosolve Cresols Crude Oil (Petroleum) Cumene Cyclohexane No. 2 Diesel Fuel Ethyl Acetate Ethyl Acrylate Ethyl Alcohol Ethyl Benzene Ethyl Dichloride Ethyl Ether Gasoline Heptane Hexane Isobutyl Acetate Isobutyl Alcohol Isopropyl Acetate Isopropyl Alcohol Jet Fuel and Kerosene Methyl Alcohol Methyl Amyl Alcohol Methyl Cellosolve Methyl Ethyl Ketone Naptha Pentane Propylene Oxide Toluene Vinyl Acetate Xylene Hazardous Gases Acetaldehyde Butadiene Butane Ethene Ethylene Ethylene Oxide Hydrogen Liquefied Natural Gas (LNG) Liquefied Petroleum Gas (LPG) Propane Propylene Vinyl Chloride (Primary Source: “Urban Development Siting with respect to Hazardous Commercial/Industrial Facilities,” by Rolf Jensen and Associates, Inc., April 1982) [49 FR 5105, Feb. 10, 1984; 49 FR 12214, Mar. 29, 1984] Appendix II to Subpart C of Part 51—Development of Standards; Calculation Methods I. Background Information Concerning the Standards (a) Thermal Radiation: (1) Introduction. (2) Criteria for Acceptable Separation Distance (ASD). People in outdoor areas exposed to a thermal radiation flux level of approximately 1,500 Btu/ft 2 2 2 (3) Acceptable Separation Distance From a Potential Fire Hazard. (b) Blast Overpressure: (c) Hazard evaluation: The standards developed for the protection of people and property are given in the following table. Thermal radiation Blast overpressure Amount of acceptable exposure allowed for building structures 10,000 BTU/ft 2 0.5 psi. Amount of acceptable exposure allowed for people in open areas 450 BTU/ft 2 0.5 psi. Problem Example The following example is given as a guide to assist in understanding how the procedures are used to determine an acceptable separation distance. The technical data are found in the HUD Guidebook. Liquid propane is used in the example since it is both an explosion and a fire hazard. In this hypothetical case a proposed housing project is to be located 850 feet from a 30,000 gallon liquid propane (LPG) tank. The objective is to determine the acceptable separation distance from the LPG tank. Since propane is both explosive and fire prone it will be necessary to determine the ASD for both explosion and for fire. The greatest of the two will govern. There is no dike around the tank in this example. Nomographs from the technical Guidebook have been reproduced to facilitate the solving of the problem. ASD For Explosion Use Figure 1 to determine the acceptable separation distance for explosion. The graph depicted on Figure 1 is predicated on a blast overpressure of 0.5 psi. The ASD in feet can be determined by applying the quantity of the hazard (in gallons) to the graph. In this case locate the 30,000 gallon point on the horizontal axis and draw a vertical line from that point to the intersection with the straight line curve. Then draw a horizontal line from the point where the lines cross to the left vertical axis where the ACCEPTABLE SEPARATION DISTANCE of 660 feet is found. Therefore the ASD for explosion is 660 feet Since the proposed project site is located 850 feet from the tank it is located at a safe distance with regards to blast overpressure. ASD For Fire To determine the ASD for fire it will be necessary to first find the fire width (diameter of the fireball) on Figure 2. Then apply this to Figure 3 to determine the ASD. Since there are two safety standards for fire: (a) 10,000 BTU/ft 2 2 To determine the fire width locate the 30,000 gallon point on the horizontal axis on Figure 2 350 feet. Now locate the 350 ft. point on the horizontal axis of Figure 3 240 feet 1,150 feet Based on this the proposed project site is located at a safe distance from a potential fireball. However, exposed playgrounds or other exposed areas of congregation must be at least 1,150 feet from the tank, or be appropriately shielded from a potential fireball. (Source: HUD Handbook, “Urban Development Siting With Respect to Hazardous Commercial/Industrial Facilities.”) [49 FR 5105, Feb. 10, 1984; 49 FR 12214, Mar. 29, 1984] Subpart D—Siting of HUD Assisted Projects in Runway Clear Zones at Civil Airports and Clear Zones and Accident Potential Zones at Military Airfields Authority: Sec. 2, Housing Act of 1949, as amended, 42 U.S.C. 1441, affirmed by sec. 2, HUD Act of 1969, Pub. L. 90-448; sec. 7(d), HUD Act of 1965, 42 U.S.C. 3535(d); OMB, Fed'l Mgmt. Cir. 75-2: Compatible Land Uses At Federal Airfields. Source: 49 FR 880, Jan. 6, 1984, unless otherwise noted. § 51.300 Purpose. It is the purpose of this subpart to promote compatible land uses around civil airports and military airfields by identifying suitable land uses for Runway Clear Zones at civil airports and Clear Zones and Accident Potential Zones at military airfields and by establishing them as standards for providing HUD assistance, subsidy or insurance. [49 FR 880, Jan. 6, 1984, as amended at 61 FR 13334, Mar. 26, 1996] § 51.301 Definitions. For the purposes of this regulation, the following definitions apply: (a) Accident Potential Zone. (b) Airport Operator. (c) Civil Airport. (d) Runway Clear Zones and Clear Zones. § 51.302 Coverage. (a) These policies apply to HUD programs which provide assistance, subsidy or insurance for construction, land development, community development or redevelopment or any other provision of facilities and services which are designed to make land available for construction. When the HUD assistance, subsidy or insurance is used to make land available for construction rather than for the actual construction, the provision of the HUD assistance, subsidy or insurance shall be dependent upon whether the facility to be built is itself acceptable in accordance with the standards in § 51.303. (b) These policies apply not only to new construction but also to substantial or major modernization and rehabilitation and to any other program which significantly prolongs the physical or economic life of existing facilities or which, in the case of Accident Potential Zones: (1) Changes the use of the facility so that it becomes one which is no longer acceptable in accordance with the standards contained in § 51.303(b); (2) Significantly increases the density or number of people at the site; or (3) Introduces explosive, flammable or toxic materials to the area. (c) Except as noted in § 51.303(a)(3), these policies do not apply to HUD programs where the action only involves the purchase, sale or rental of an existing property without significantly prolonging the physical or economic life of the property. (d) The policies do not apply to research or demonstration projects which do not result in new construction or reconstruction, to interstate land sales registration, or to any action or emergency assistance which is provided to save lives, protect property, protect public health and safety, or remove debris and wreckage. [49 FR 880, Jan. 6, 1984, as amended at 61 FR 13334, Mar. 26, 1996] § 51.303 General policy. It is HUD's general policy to apply standards to prevent incompatible development around civil airports and military airfields. (a) HUD policy for actions in Runway Clear Zones and Clear Zones. (1) HUD policy is not to provide any assistance, subsidy or insurance for projects and actions covered by this part except as stated in § 51.303(a)(2) below. (2) If a project proposed for HUD assistance, subsidy or insurance is one which will not be frequently used or occupied by people, HUD policy is to provide assistance, subsidy or insurance only when written assurances are provided to HUD by the airport operator to the effect that there are no plans to purchase the land involved with such facilities as part of a Runway Clear Zone or Clear Zone acquisition program. (3) Special notification requirements for Runway Clear Zones and Clear Zones. In all cases involving HUD assistance, subsidy, or insurance for the purchase or sale of an existing property in a Runway Clear Zone or Clear Zone, HUD (or the responsible entity or recipient under 24 CFR part 58) shall advise the buyer that the property is in a Runway Clear Zone or Clear Zone, what the implications of such a location are, and that there is a possibility that the property may, at a later date, be acquired by the airport operator. The buyer must sign a statement acknowledging receipt of this information. (b) HUD policy for actions in Accident Potential Zones at Military Airfields. HUD policy is to discourage the provision of any assistance, subsidy or insurance for projects and actions in the Accident Potential Zones. To be approved, projects must be generally consistent with the recommendations in the Land Use Compatibility Guidelines For Accident Potential Zones [49 FR 880, Jan. 6, 1984, as amended at 61 FR 13334, Mar. 26, 1996] § 51.304 Responsibilities. (a) The following persons have the authority to approve actions in Accident Potential Zones: (1) For programs subject to environmental review under 24 CFR part 58: the Certifying Officer of the responsible entity as defined in 24 CFR part 58. (2) For all other HUD programs: the HUD approving official having approval authority for the project. (b) The following persons have the authority to approve actions in Runway Clear Zones and Clear Zones: (1) For programs subject to environmental review under 24 CFR part 58: The Certifying Officer of the responsible entity as defined in 24 CFR part 58. (2) For all other HUD programs: the Program Assistant Secretary. [61 FR 13335, Mar. 26, 1996] § 51.305 Implementation. (a) Projects already approved for assistance. This regulation does not apply to any project approved for assistance prior to the effective date of the regulation whether the project was actually under construction at that date or not. (b) Acceptable data on Runway Clear Zones, Clear Zones and Accident Potential Zones. The only Runway Clear Zones, Clear Zones and Accident Potential Zones which will be recognized in applying this part are those provided by the airport operators and which for civil airports are defined in accordance with FAA regulations 14 CFR part 152 or for military airfields, DOD Instruction 4165.57, 32 CFR part 256. All data, including changes, related to the dimensions of Runway Clear Zones for civil airports shall be verified with the nearest FAA Airports District Office before use by HUD. (c) Changes in Runway Clear Zones, Clear Zones, and Accident Potential Zones. If changes in the Runway Clear Zones, Clear Zones or Accident Potential Zones are made, the field offices shall immediately adopt these revised zones for use in reviewing proposed projects. (d) The decision to approve projects in the Runway Clear Zones, Clear Zones and Accident Potential Zones must be documented as part of the enviornmental assessment or, when no assessment is required, as part of the project file.