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LO2 / LH2
1.6
1.4
1.2 1
0.8
0.6
0.4
0.2 0 Impact Speed (ft/s) Yield Factor 0 100 200 300 400 500 600 700 800 900 1000
09/10/2024 AC 450.137-1
7.3 L iquid Propellant Yield.
7.3.1 A screening analysis should use the Project PYRO results shown in Fig. 1 to compute an upper-bound yield factor as a function of impact velocity for three common combinations of oxidizer and fuel:
1. Cryogenic liquid oxygen and liquid hydrogen (LOX/LH2).
2. Cryogenic liquid oxygen and Rocket Propellant–1 (LOX/RP-1).
3. Hypergolic propellants, consisting of a liquid oxidizer such as nitrogen tetroxide (N2O4) or inhibited red fuming nitric acid (IRFNA) combined with a liquid fuel such as monomethyl hydrazine (MMH), unsymmetrical dimethyl hydrazine (UDMH) or Aerozine-50 (A50).
7.3.2 The yield factor is defined as the ratio of the equivalent weight of TNT to the weight of the propellant involved in the explosion, based on the air shock overpressure generated in surface level (hemispherical) explosions. The yield factors are expressed as functions of the impact velocity magnitude, i.e., the speed at which the propellant tanks impact the surface causing breakup. The terms ‘impact velocity’ and ‘impact speed’ are used interchangeably in this context.
Figure 1 – Yield Curve for Impacts of Li quid Oxygen and Liquid Hydrogen Propellant
7.3.3 Data from actual launch vehicle impacts show that for public safety purposes, impacts on soft surfaces, including sand, soft soil, and water, may be treated as hard surface impacts. Consequently, no distinction between the two types of surfaces is required.
Thus, Table 1 of this AC shows the data points that should be used to construct piecewise linear functions for the yield factor from any impact of these three liquid propellants.
T able 1 ‒ Liquid Propellant Yield Model Tabular Values LOX/LH2 Impact Yield Speed Factor fps lb. TNT/lb.
LOX/RP1 Impact Yield Speed Factor fps lb. TNT/lb.
Hypergols Impact Yield Speed Factor fps lb. TNT/lb.
0 0.16 0 0 0 0.020 85 0.16 170 0.215 100 0.085 745 1.50 800 0.215 200 0.135 800 1.50 300 0.180 400 0.220 500 0.245 600 0.260 700 0.275 800 0.280
7.3.4 Although some liquid monopropellants are used in rocket propulsion, liquid propellants for which yield factor models have been developed for use in FFBO risk analysis are most commonly bipropellants. These consist of separate fuel and oxidizer components that are combined in liquid propellant engines to propel the vehicle. For other propellant types, the explosive yield factor curve should be based on the best available explosive yield data for the corresponding type or class of solid or liquid propellant based on empirical data or computational modeling. The TNT equivalence for explosive events addressed in defense explosives safety regulation (DESR) 6055.93 are considered valid by the FAA; applicants should consult with the FAA to determine when these scenarios are deemed applicable by the FAA.
7.4 Solid Propellant Yield
7.4.1 Solid propellants relevant for flight safety analysis are typically represented in one of two categories: Hazard Division (HD) 1.1 detonable propellants, or HD 1.3 deflagration propellants4. For other types of solid propellant, a conservative option is to apply the HD 1.1 model. The yield factors for solid propellant should account for the size and shape of the propellant, type of impact surface, total impact speed, and orientation at impact if applicable.
7.4.2 For HD 1.1 impacts, yield factor FTNT values for various surface types should be based on Figure 2 of this AC. This plot indicates that the factor will either be 0 or 1.25 depending on the impact velocity. These curves make no distinction of whether the propellant is in a contained motor, its impact orientation, or uncontained hazardous debris created at vehicle breakup.
3 Department of Defense DOD Defense Explosives Safety Regulation (DESR), DoD 6055.09, Edition 1, Change 1, Department of Defense Explosives Safety Board (DDESB), dated February 23, 2024.
4 Title 49, Code of Federal Regulations, Subpart B, Chapter 1, Subchapter C, Part 173.
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,::, 60 Q) - >= 40 - 20 - 140 21C 250 370 0 I I I I I I I 0 100 200 300 400 500 700 80 Pro act Veloci 09/10/2024 AC 450.137-1 Figure 2 – Hazard Division 1.1 Propellant Yield Model
7.4.3 For HD 1.3 propellant impacts5, the screening analysis should assume that all solid rocket motors remain intact and impact in a side-on orientation. Yield factors for intact motor segments that impact on sand in a side-on orientation may be obtained from the curves in Figure 3 of this AC, where the segment sizes are measured by the lateral diameter of the motors. If the yield factor associated with the desired motors is not those presented in the figure or are not available, then the curves in Figure 3 of this AC should still be used. For other motor diameters between 41” and 146,” linearly interpolate between the nearest bounding curves. For diameters outside the range, use the closest bounding curve and do not extrapolate.
5 Title 49, Code of Federal Regulations, Subpart B, Chapter 1, Subchapter C, Part 173.
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0.00 0 100 200 300 400 500 600 700 800 900 Impact Speed (ft/s)
- 4111 Segment
- 6011 Segment
- 9211 Segment
- 12411 Segment
- 14611 Segment 09/10/2024 AC 450.137-1 Figure 3 ‒ Yield Curves for HD 1.3 Propellant The following equation should be used to compute the yield factors as a function of impact speeds for a variety of motor sizes that use HD 1.3 propellants.
𝑇𝑇𝑇𝑇𝑇𝑇 𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌𝑌 𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹 = 𝐹𝐹𝑆𝑆4 + 𝑏𝑏𝑆𝑆3 + 𝐹𝐹𝑆𝑆2 + 𝑌𝑌𝑆𝑆+e where S = Impact speed (feet per second) a-e = Equation coefficients (pounds TNT per pound propellant)
7.4.4 Tables 3, 4, and 5 in appendix A of this AC list the coefficients that should be used with this equation to compute the yield factor for side-on motor impacts on sand.
7.4.5 For surface types other than sand or soft soil impact, adjust the impact speed by:
𝑣𝑣𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑣𝑣 = 𝐹𝐹𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑖𝑖𝑖𝑖𝑠𝑠 where is 𝐹𝐹𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑖𝑖𝑖𝑖𝑠𝑠 0.55 for steel, 0.78 for concrete, 1.00 for sand, and 1.61 for water.
7.5 Sy mpathetic Yields.
7.5.1 The maximum credible yield should account for the potential for sympathetic yields when multiple motors and/or engines can impact near one another during the same event. If the motors or engines have different propellant compositions, then the yields should be computed separately, and not combined to estimate the maximum credible yield. If a vehicle that uses multiple motors or engines with the same propellant composition is expected to impact intact, then the propellant involved in the explosion should account for the total of all the propellants on the vehicle unless the applicant can demonstrate that a vehicle impact would result in explosions that are sufficiently separated by time or distance to be treated as separate explosions for the purpose of an FFBO analysis. For example, explosions that are coincident in terms of location, but are separated by at least 0.3 seconds may be treated as separate explosions. If insufficient information exists for such an evaluation, then the screening analysis should combine the propellant weights and use this as a single yield.
7.5.2 In accordance with § 450.137(c)(2), an application must include, at a minimum, a description of the methods used to compute the foreseeable explosive yield probability pairs, and the complete set of yield-probability pairs, used as input to the far-field overpressure analysis. A deterministic screening method should assume a probability of one for the maximum credible yield.
7.6 Exposed Windows and Populations Susceptibility to Injury.
7.6.1 In accordance with § 450.137(b)(3), an analysis must account for the characteristics of exposed windows and the population’s susceptibility to injury. Thus, a critical input to any valid screening method is a description of the population centers and potentially inhabited structures that could be subject to an FFBO hazard.
7.6.2 In general, an FFBO analysis should use population data that complies with the requirements of § 450.123. AC 450.123-1 provides guidance on population analyses that could be used to establish the population input data for FFBO screening analysis.
7.6.3 In accordance with § 450.123(a), an FSA must account for the distribution of people for the entire region where there is a significant probability of impact of hazardous debris.
The extent of the region should consider all types of hazardous debris (as defined in § 401.7), which accounts for hazards from explosive and toxic substances, as well as potential for consequences due to either planned operations (e.g., jettisons) or reasonably foreseeable failures.
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09/10/2024 AC 450.137-1
7.6.4 T o identify the extent of the region that includes population centers and potentially inhabited structures that could be susceptible to an FFBO hazard, the applicant should compute the distance between the maximum credible explosive yield event location for each phase of flight and the point where the peak incident overpressure would not exceed 200 Pa under focusing conditions with a focus factor equal to 2.0, referred to here as the maximum range of the FFBO hazard. Figure 4 of this AC (replicated from Figure 5.2.5 of the IAASS publication) shows that the 69 Pa (0.01 psi) peak incident overpressure threshold corresponds to a negligible probability of breakage for typical populations surrounding the two major launch sites in the U.S. In addition, ANSI Standard S2.20-19836 reported this threshold peak incident overpressure corresponds “in practice to the threshold level at which claims for window damage begin” based on recordings from nuclear tests.
Figure 4 – Probability of breakage for average windowpanes near Vandenberg, CA and Cape Canaveral, FL7 6 American National Standard ANSI S2.20-1983, Estimating Airblast Characteristics for Single Point Explosions in Air, with a Guide to Evaluation of Atmospheric Propagation and Effects, Standards Secretariat, Acoustical Society of America, New York, NY, 1983.
7 Figure 5.2.5 of Allahdadi, Firooz A., Isabelle Rongier, Tommaso Sgobba, and Paul D. Wilde, Safety Design for Space Operations, Sponsored by The International Association for the Advancement of Space Safety (IAASS), Elsevier, Watham, MA, dated 2023.
7.6.5 A screening analysis should use the following equation (which is equation 14 in the IAASS publication) to compute the distance from between the maximum credible explosive yield event location for each phase of flight and the point where the peak incident overpressure would not exceed 69 Pa under focusing conditions with a focus factor equal to 2.0.
∆𝑃𝑃 = �𝐹𝐹𝑠𝑠𝑓𝑓𝑖𝑖�1.864(105)(𝐹𝐹𝐻𝐻𝐻𝐻𝐻𝐻𝑊𝑊)0.4𝑅𝑅−1.2 ∆𝑃𝑃 = Incident peak blast overpressure in Pascals (Pa) 𝐹𝐹𝑠𝑠𝑓𝑓𝑖𝑖 = Focus factor 𝑅𝑅 = Nearest distance from explosion to population center in meters 𝑊𝑊 = Net explosive yield (charge weight) in kg TNT 𝐹𝐹𝐻𝐻𝐻𝐻𝐻𝐻 = Height of Burst factor, which is 2 for a ground explosion
7.6.6 A screening analysis should use a Height of Burst factor of 2, which conservatively represents a perfect reflection from a hard surface.
7.6.7 For each phase of flight where an explosion is foreseeable, the screening method should identify the population centers within the maximum range of the FFBO hazard of the maximum credible explosive event. In addition, for any single potentially inhabited structure within the distance defined by the “no-damage yield” for a single residence based on Figure 5 of this AC (replicated from Figure 5.2.3 of the IAASS publication), the screening method should identify the number, size, and type of windows that face within 90 degrees of the azimuth from the maximum credible explosive yield location to the single structure location. The screening analysis should identify windows of different types and differentiate between annealed, tempered, dual paned and film covered. Window size categories should be based on typical windows found in the local populated areas and differentiate between pane areas that differ by a factor of two at the most.
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1.00 10.00 100.00 Distance km 09/10/2024 AC 450.137-1 Figure 5 ‒ No-damage limits for surface explosions (ANSI standard Figure 26)8 8 Figure 5.2.3 of Allahdadi, Firooz A., Isabelle Rongier, Tommaso Sgobba, and Paul D. Wilde, Safety Design for Space Operations, Sponsored by The International Association for the Advancement of Space Safety (IAASS), Elsevier, Watham, MA, dated 2023.
7.6.8 I f the total area of annealed glass panes that face the maximum credible explosive yield location for a given phase of flight exceeds 40 square feet (which is typical for a residence), then the screening method described in this AC cannot be used to satisfy the requirements of § 450.137 for that phase of flight.
7.6.9 Populations located in vehicles that meet U.S. standards need not be accounted for in an FFBO screening analysis (because the glass used in U.S. vehicles are not a credible source of FFBO hazards). The FFBO can also ignore any population centers that would be subject to a peak incident overpressure above 1.0 psi or 6894 Pascal (Pa), given the maximum credible explosive event because § 450.137(b)(3) requires the FFBO analysis to account for the potential for broken windows due to peak incident overpressures below 1.0 psi only. However, any population center exposed to a peak incident overpressure above 1.0 psi given the maximum credible explosive event, including people in vehicles that meet U.S. standards, would generally need to be accounted for in the debris risk analysis in accordance with § 450.135.
7.7 Deterministic Screening Method.
7.7.1 If the maximum credible yield input (developed in accordance with paragraph 7.5 of this AC) to the deterministic no-damage yield analysis (shown in Figure 5 of this AC) indicates that no public population centers are vulnerable to window breakage, then the hazards from FFBO are negligible, and the FFBO analysis complies with §§ 450.137(a)(1) and (b) based on this deterministic screening method.
7.7.2 A simple example of the deterministic screening method results is summarized in Table 2 of this AC. In this case, the maximum credible yield was determined to be 1,000 Kg TNT equivalent at the launch point. The closest population centers are
1. A single residence 3 km away from the launch point,
2. A village of 100 people 8 km away from the launch point,
3. A small town of 10,000 people 40 km away from the launch point, and
4. A city of 1,000,000 people 150 km away.
7.7.3 This is an example where the deterministic method demonstrates negligible FFBO risks because the actual distance from the closest edge of each population center to the location of the maximum credible yield event exceeds the distance corresponding to the “no damage yield” given by Figure 5 of this AC as shown in the Table 2.
Table 2 ‒ Sample Description of Results from the Deterministic Screening Method P opulation Center Name Number of People Distance from population center to explosion (km) No Damage Distance (km) Closest Residence <=4 3 2.2 Village 100 8 7 Small Town 10,000 40 30 City 1,000,000 150 130 19
8 SAT
ISFYING APPLICATION REQUIREMENTS A far-field overpressure risk analysis submitted for compliance with the safety criteria in § 450.101 must be sufficiently documented by an operator in their application for a launch or reentry license to show that related regulatory requirements have been met.
This analysis should include a description of the far-field overpressure analysis, including all assumptions and justifications for the assumptions, analysis methods, input data, and results. The following sections describe the minimum details that the application should provide and sample calculations for a simplified screening analysis.
8.1 Terrain and Population Data.
8.1.1 In accordance with § 450.137(c)(1), a far-field overpressure risk analysis submitted for compliance with the safety criteria in § 450.101 must include a description of the relevant characteristics of the general region surrounding the explosion used as input to the far-field overpressure analysis, including a description of population centers, terrain, building types, and window characteristics. To fulfill this application requirement using the screening methods identified in the AC, an applicant should provide the following.
1. A list that includes the location (latitude and longitude) and population of each population center that contains at least one potentially inhabited structure within the maximum range of the FFBO hazard for each phase of flight. The population of any population center that consists of a single residential structure should be listed as less than or equal to four in the absence of more accurate information.
2. A list of the number, size, and type of windows that face within 90 degrees of the azimuth from the maximum credible explosive yield location to the single structure location for each potentially inhabited structure within the distance defined by the “no-damage yield” for a single residence and the maximum credible explosive yield based on Figure 5 of this AC (replicated from Figure 5.2.3 of the IAASS publication). The description of window types should differentiate between annealed, tempered, dual paned and film covered. Window size categories should be based on typical windows found in the local populated areas and differentiate between pane areas that differ by a factor of two at the most.
3. A table, such as shown in Table 2 of this AC, that identifies the closest population centers to each maximum credible explosion location that have populations of at least 100, 1,000, 10,000, 100,000, and 1,000,000 people, as well as the closest single potentially inhabited structure.
4. A general description of the building types located in each of the population centers listed in the table provided to identify the closest population (in response to #3 of this list). The general description should identify, at a minimum, the following structure types located within each population center: mobile homes and trailers, single family residences, multi-family residences with no more than three-stories, residential structures with more than three-stories, commercial buildings of all kinds with no more than three-stories (including retail, offices, restaurants, gas stations, strip malls) and commercial and industrial buildings of all kinds with more than three -stories (including large retail, offices, warehouses, manufacturing, and malls).
5. A general description of the terrain within the maximum range of the FFBO hazard for each phase of flight. The general description should identify, at a minimum, the following terrain types: flat with land and/or water boundaries, and hilly with maximum elevation change.
8.1.2 In accordance with § 450.137(c), a far-field overpressure risk analysis must include description of the far-field overpressure analysis, including all assumptions and justifications for the assumptions, analysis methods, and input data. To fulfill this application requirement using the screening methods identified in the AC, an applicant should provide the following.
1. A description of the source of the data provided above, such as census data, physical surveys, and satellite imagery.
2. A description of the dates for the source data, and any methods used to update the data to account for changes that could occur prior to the date of the operation.
8.2 Explosive Yield-Probability Pairs.
8.2.1 In accordance with § 450.137(c)(2), a far-field overpressure risk analysis must include a description of the methods used to compute the foreseeable blast yields probability pairs, and the complete set of yield-probability pairs, which are used as input to the far-field overpressure risk computations. Thus, an FFBO should include a description of how the explosive yield was computed for all phases of flight where an FFBO hazard was analyzed.
8.3 Overpressure Computations.
8.3.1 In accordance with § 450.137(c)(3), a far-field overpressure risk analysis must include a description of the methods used to compute peak incident overpressures as a function of distance from the explosion and prevailing meteorological conditions, including sample calculations for a representative set of the foreseeable meteorological conditions, yields, and population center distances from the explosion.
8.3.2 For a screening analysis performed in accordance with this AC, an FFBO analysis should:
1. Identify the equation used to peak incident overpressures as a function of distance
(i.e., equation).
2. A list of the input and output values for the equation used to compute the peak incident overpressure for each of the closest population centers that have populations of at least 100, 1,000, 10,000, 100,000, and 1,000,000 people, as well as the closest single potentially inhabited structure.
3. List the maximum range of the FFBO hazard analysis for each phase of flight.
4. Note that the prevailing meteorological conditions were conservatively assumed to produce caustic focusing on every population center within the maximum range of the FFBO hazard for each phase of flight.