Barrier Design Guidance

For

HUD Assisted Projects Near Hazardous Facilities

Guidebook 6600.G

Environmental Planning Division

Office of Environment and Energy
i

Table of Contents Pages

I – Introduction 1-2

II - Basic guidance requirement 3

III – Exclusions and Limitations of this guidance 4

IV - Applications of this guidance 5

V – Definitions 6-9

VI - Units of measure 10-11

VII - Basic mitigation principles 12

VIII - Basic barrier principles 13-14

IX - Guidelines for the users of this document 15-31

X - Mitigation example 32-36

XI - Table with density values of most common substances 37-40

XII - Table with heat of combustion values for common fuels 41-42

XIII - Table with fuel vapor density values for hydrocarbon fuels 43

References 44-45
1

I – Introduction

A. Purpose

This guidance is intended to provide U.S. Department of Housing and Urban 

Development (HUD) grantees with information regarding barrier design that will protect 

HUD-assisted projects from facilities that may pose an explosive or flammable hazard. It 

provides an analytical foundation and structure towards the understanding of the basic 

requirements behind the design of a barrier for mitigation. It identifies the information 

required and analytical guidelines for designing the required protection against blast 

overpressure and thermal heat flux produced by stationary hazards covered under 24 

CFR Part 51 Subpart C.

Only a licensed professional engineer (civil or structural) should design and oversee the 

construction of mitigation barriers.

This guidance was prepared primarily for civil or structural engineers. For people of other 

professional backgrounds, this guidance provides procedures for calculating the 

required information the licensed professional will need for designing the required 

barrier for mitigation.

The “required information” this guidance refers to for the design of barriers for 

mitigation includes the theoretical and mathematical procedures for the 

determination of barrier design criteria based on the standards of blast 

overpressure and thermal radiation within the regulation 24 CFR Part 51 Subpart 

C. This guidance makes reference to the following barrier design criteria: 

Peak Positive Incident Pressure, and

Thermal Heat Flux

This guidance is not intended to provide information in reference to barrier 

dimensions, materials for construction, or how to construct a barrier for 

mitigation.

B. Background

The regulation 24 CFR Part 51 Subpart C covers technical requirements for determining 

Acceptable Separation Distances (ASD’s) from HUD-assisted projects in close proximity 

to hazardous operations. These hazardous operations include the storage, handling or 

processing of substances of hazardous nature that have the potential to cause an 

explosion or fire.

Once the Acceptable Separation Distance (ASD) has been calculated, the next common 

question from HUD grantees is whether the project site provides the ASD required by 

the regulation. If the ASD is not available, consideration of possible mitigation is the 

next step in the process towards site compliance within HUD standards.
24 CFR Part 51 Subpart C Barrier Design Guidance

2

A detailed site mitigation analysis is recommended for proposed HUD-assisted project

sites in proximity to facilities that store, process or handle materials of fire or explosive 

nature. If the site mitigation analysis reveals that there is no mitigation option other than 

the design and implementation of a barrier, this guidance provides the required technical 

information to help HUD grantees and licensed professionals to design the barrier for the 

HUD-assisted project. 

HUD standards are set for thermal radiation and blast overpressure (24 CFR Part 

51.203). These standards are applicable to the following:

Thermal Radiation 

o Structures - 10,000 BTU/ft2-hr 

o People – 450 BTU/ft2-hr

Blast Overpressure–

o Structures - 0.5 psi

To protect buildings and housing units from thermal radiation, HUD established the 

thermal radiation standard of 10,000 BTU/ft2-hr.

To protect people in outside areas, such as patios or common areas, or in places where 

communities congregate, like parks or recreation areas, HUD established the thermal 

radiation standard of 450 BTU/ft2-hr. If no mitigation exists or is implemented, it is 

required to build HUD-assisted projects to the ASD at which the thermal radiation flux 

will not exceed 450 BTU/ft2-hr.

Blast overpressure can harm people or destroy buildings if this pressure is higher than

0.5 psi. For proposed HUD-assisted project sites where there are stored hazards that 

can cause blast overpressures and no mitigation, it is required to build to the ASD at 

which this pressure is no higher than 0.5 psi.

Barriers as a mitigation measure are expensive and have other drawbacks. If the ASD is 

achievable, or better mitigation can be used, HUD advises that construction of a barrier 

be avoided.
24 CFR Part 51 Subpart C Barrier Design Guidance

3

II – Basic Guidance requirement

A. This guidance can be applied to the following activities:

HUD-assisted projects as defined at 24 CFR 51.201.

o These are projects for residential, institutional, recreational, commercial 

or industrial use that conduct development, construction, rehabilitation, 

modernization or conversion with HUD subsidy, grant assistance, loan, 

loan guarantee, or mortgage insurance.

o For purposes of Subpart C, the terms “rehabilitation” and modernization” 

refer only to such repairs and renovation of a building or buildings as will 

result in an increased number of people being exposed to hazardous 

operations by increasing residential densities, converting the type of use 

of a building to habitation, or making a vacant building habitable. In 

regards to building or buildings, for purposes of this Subpart, the repairs 

and renovation also applies to other projects for HUD-funding assistance.

 B. Entities and personnel who will benefit from this guidance are:

Planners

Developers

Engineers

HUD field and headquarters staff

HUD grantees
24 CFR Part 51 Subpart C Barrier Design Guidance

4

III – Exclusions and Limitations of this Guidance

1. This guidance does not apply in the following situations, which are excluded from Part 

51 Subpart C:

a. Underground Storage Containers – If the hazard is entirely buried, there is no need for 

an ASD.

b. Stationary containers of 100 gallons or less capacity containing common liquid 

industrial fuels - Results from the December 19, 1981 study1from Rolf Jensen and 

Associates (RJ&A), Deerfield, Illinois demonstrated that stationary containers of 100

gallons or less capacity containing common liquid industrial fuels (such as gasoline, fuel 

oil, kerosene and crude oil) do not emit thermal radiation heat flux effects at levels that 

would pose a danger to HUD-assisted projects. The regulation 24 CFR 51.201, under 

the “hazard” definition, lists various exceptions to Subpart C of 24 CFR Part 51. 

However, the exception of stationary aboveground containers of 100 gallons or less 

capacity containing common liquid industrial fuels, applies only to containers of 100 

gallons or less capacity, that are aboveground and stationary, containing common liquid 

industrial fuels only, such as gasoline, fuel oil, kerosene and crude oil. This exception 

does not apply to aboveground stationary containers containing hazardous gases, as 

listed in Appendix I of the Regulation or in this guidance.

c. Natural gas holders with floating tops – These are stationary aboveground storage 

containers used to store natural gas. These containers are less susceptible to corrosion 

and tank perforations that can cause Bleves (rupture explosions).

d. Mobile conveyances (tank trucks, barges, railroad tank cars) – Containers that are 

mobile, with capacity of storing common liquid industrial fuels or hazardous gases as 

listed in Appendix I of the regulation 24 CFR Part 51 Subpart C. 

e. Pipelines, such as high pressure natural gas transmission pipelines or liquid 

petroleum pipelines – Pipelines that transmit hazardous substances are not considered 

a hazard under 24 CFR Part 51 Subpart C if they are located underground or if they 

comply with applicable Federal, State or local safety standards.

2. This guidance applies subject to the following limitation:

Self-Contained Above Ground Containers (SCACs) for calculation of the ASD 

SCACs have two external walls, the first wall has the purpose of containing the product, 

the second serves as spill prevention to the outside of the container if the first wall 

ruptures. The interstitial space (space between the first and the second wall) serves as 

containment of the container’s product if there is a rupture in the container’s internal wall.

SCACs are considered containers without a dike, and calculations must be done as 

for containers without a dike area.

.

 

1 Urban Development Siting with Respect to Hazardous Commercial/Industrial Facilities
24 CFR Part 51 Subpart C Barrier Design Guidance

5

IV – Applications of this Guidance 

The regulation 24 CFR Part 51, Subpart C and this guidance apply only to aboveground 

stationary containers 

1) of more than 100 gallon capacity, containing common liquid industrial fuels

listed along with other hazardous substances, in Appendix I of the Regulation

and the HUD hazards guidebook “Siting of HUD-Assisted Projects Near 

Hazardous Facilities”; and 

2) of any capacity, containing hazardous liquids or gases that are not common 

liquid industrial fuels. (See also the list of hazardous substances located in 

Appendix I of the Regulation and the HUD hazards Guidebook). Keep in mind 

that you may be required to comply with Part 51 for hazardous substances that 

are not listed.

The formula provided to calculate the thermal heat flux (Q), can be applied only to 

stationary aboveground storage containers under pressure, with or without a dike. The 

dike area does not have any effect on the Acceptable Separation Distance (ASD) 

calculations when the container being analyzed is under pressure.

To calculate the thermal heat flux (Q) from stationary aboveground containers not under 

pressure, please contact Headquarters (Office of Environment and Energy, Nelson A. 

Rivera – 202-402-4455). The variables impacting such a type of fire’s behavior are: 

1) Changes in chemical properties of stored substances not under pressure; and 

2) Outside ambient conditions (wind direction and speed). 

A mathematical procedure pertaining to these variables would be extremely complex 

and unreliable.
24 CFR Part 51 Subpart C Barrier Design Guidance

6

V- Definitions

Acceptable Separation Distance (ASD) – Under 24 CFR Part 51 Subpart C, the

minimum distance from a hazardous operation to where a HUD-assisted project

(including open spaces related to the HUD-assisted project, where people congregate) 

can be located in accordance with HUD’s standards of blast overpressure (0.5 psibuildings) and thermal radiation (450BTU/ft2 

– hr – people and 10,000 BTU/ft2– hr –

buildings). In addition, it is the minimum distance that HUD-assisted projects involving 

the installation of hazardous facilities can be located from existing or planned residences 

or from any other facility or area where people may congregate or be present.

Barrier – A barrier designed to sustain blast overpressure (generated pressure from an 

explosion of a substance contained under pressure) from a substance stored under 

pressure undergoing a liquid-gas unbalanced reaction or thermal radiation (generated 

heat from the effects of combustion from a flammable substance) or both (blast 

overpressure and thermal radiation). The design, location and implementation of the 

barrier it is not the same for all cases; the nature of the barrier varies depending on the 

results of the analysis of the location of the proposed HUD-assisted project site.

Blast Overpressure (also known as Peak Positive Incident Pressure (Ps)) – Exerted 

pressure from a compressed liquid (or liquid-gas mixture) inside a container after an 

incident occurs (usually tank perforation due to corrosion or impact) that prompts a 

liquid-gas unbalanced reaction and the container to explode with high energy.

Bleve – The type of explosion that occurs when a vessel containing a pressurized liquid 

is ruptured. A bleve can occur in a vessel that stores a substance that is usually a gas at 

atmospheric pressure but is a liquid when pressurized (for example, liquefied petroleum 

gas). The substance will be stored partly in liquid form, with a gaseous vapor above the 

liquid filling the remainder of the container. If the vessel is ruptured (for example, due to 

corrosion or failure under pressure) the vapor portion may rapidly leak, dropping the 

pressure inside the container and releasing a wave of overpressure from the point of 

rupture. The sudden drop in pressure inside the container causes a liquid-gas 

unbalanced reaction which produces large amounts of vapor combined with large 

pressures in the process. 

Buried Container (or underground storage container) - Any one or combination of 

containers (including underground pipes connected thereto) that is used to contain a 

regulated substance or an accumulation of regulated substances, and is located beneath 

the surface of the ground. Underground storage containers are not considered to be a 

hazard under 24 CFR Part 51 Subpart C, this guidance or the ASD assessment tool for 

the calculation of the ASD from a hazard for a HUD-assisted project.

Combustion – A complex sequence of chemical reactions among oxygen, a fuel source 

and an ignition source resulting in the production of heat and light in the form of glow or 

flames.

Container – A structure (also known as a vessel, tank or enclosure) built to contain 

material in liquid, gas or solid state, that can be designed for stationary or for transport 

purposes. If this structure contains a product under pressure (this includes gases and 
24 CFR Part 51 Subpart C Barrier Design Guidance

7

liquefied gases that are kept in their liquid state maintained at very low temperatures) it 

is called a vessel; for liquid or solid products, it is called a tank or an enclosure. 

Note: Commercially, containers used to hold liquids, solids or gases, are all

referred to as tanks. Technically speaking, however, containers that hold solids 

or liquids are properly referred to as tanks or enclosures, and those for gases, as 

vessels.

Cryogenics - The branches of physics and engineering that involve the study of very 

low temperatures, how to produce them, and how materials behave at those 

temperatures.

Dike – A continuous wall (built out of soil, asphalt, steel or concrete), surrounding a 

container, constructed as a defense or as a boundary to provide containment or 

impoundment during a spill. The dike completes the containment within the diked area 

and serves as the diked area perimeter. The combination of the diked area and the dike 

provide spill protection.

Diked area - The area between the container’s outside wall and the dike. The dike area 

provides containment if there is container rupture, causing a spill.

Hazard – Is a stationary operation or facility within a 1-mile surrounding distance from a 

HUD-assisted project site where chemicals of flammable or explosive nature are 

handled, stored or manufactured in aboveground containers. 

Hazardous Gas – The state of matter distinguished from the solid and the liquid states 

by relatively low density and viscosity, relatively great expansion and contraction with 

changes in pressure and temperature, the ability to diffuse readily, and the spontaneous 

tendency to become distributed uniformly throughout any container. This state of matter 

as being hazardous means that its properties defines this gas to impact the human 

health or the environment because it is flammable, toxic or of radioactive nature.

Hazardous Liquid - The state of matter in which a substance exhibits a characteristic 

readiness to flow, little or no tendency to disperse, and relatively high incompressibility. 

Hazardous Products (or substances) – Are those flammable and combustible gases or 

liquids which upon accidental release and ignition or explosion pose a threat to public 

safety or damage to property.

Liquefied Natural Gas (LNG) – A natural gas that has been processed to remove either 

valuable components, e.g., helium, or those impurities that could cause difficulty 

downstream, e.g., water, and heavy hydrocarbons and then condensed into a liquid at 

almost atmospheric pressure (transport pressure around 25 kPa) by cooling it to

approximately -163 degrees Celsius. LNG is transported by specially designed cryogenic 

sea vessels and cryogenic road tankers; and stored in specially designed tanks.

Liquefied Petroleum Gas (LPG) – A mixture of hydrocarbon gases (also called 

liquefied petroleum gas, liquid petroleum gas, LPG, LP Gas, or autogas) used as a fuel 

in heating appliances and vehicles, and increasingly replacing chlorofluorocarbons as an 

aerosol propellant and a refrigerant to reduce damage to the ozone layer. Varieties of 
24 CFR Part 51 Subpart C Barrier Design Guidance

8

LPG bought and sold include mixes that are primarily propane, mixes that are primarily 

butane, and mixes including both propane and butane, depending on the season. In the 

winter a mix contains more propane and in the summer a mix contains more butane. 

Heat of Combustion – The energy released as heat when a compound undergoes 

complete combustion with oxygen. The chemical reaction is typically a hydrocarbon 

reacting with oxygen to form carbon dioxide, water and heat. 

Mitigation – The process for implementing the required level of protection to a HUDassisted project site from stationary hazardous operations which store, handle or 

process materials of explosive or flammable nature. This level of protection can be 

either designed and implemented (as a designed barrier) or it can be a preexisting 

barrier, either natural (mountains, hills) or man-made (elevated buildings or housing 

developments).

Peak Positive Incident Pressure (Ps) – Blast overpressure

Scaled Distance – A calculated distance, requiring the input parameters of the standoff 

distance and the hazard’s equivalent weight of TNT (Trinitrotoluene-useful explosive 

material with convenient handling properties). This distance is plotted in a special graph 

for the determination of the peak positive incident pressure.

Self-Contained Above Ground Containers (SCACs) – Containers with interstitial spill 

countermeasure systems for spill prevention control. SCACs have two external walls, 

the first wall has the purpose of containing the product of the container, the second 

serves for spill prevention to the outside of the container if the first wall ruptures. The 

interstitial space (space between the first and the second wall) serves as containment of 

the container’s product if there is a rupture in the container’s internal wall.

Standoff Distance – For the calculation of the thermal heat flux and the peak positive 

incident pressure, the standoff distance means:

For the thermal heat flux calculation – Standoff distance is the calculated 

distance from the center of the fireball to the target. The target can be the 

perimeter of the proposed HUD-assisted project site or where the fire barrier can 

be implemented.

For the peak positive incident pressure calculation – Standfoff distance is the 

measured distance from the center of the container (hazard) being assessed to 

the target. The target can be the perimeter of the proposed HUD-assisted project 

site or where the blast barrier can be implemented. 

Thermal Heat Flux (Q) – Amount of heat being radiated from a source. In other words, 

the heat wave generated from combustion.

Thermal Radiation – Process by which energy is emitted by a warm or hot surface. The 

energy is electromagnetic radiation and travels at the speed of light and does not require 

a medium to carry it. Thermal radiation ranges in frequency from infrared rays through 

visible light to ultraviolet rays. The intensity and frequency distribution of the emitted rays 
24 CFR Part 51 Subpart C Barrier Design Guidance

9

are determined by the nature and temperature of the emitting surface; in general, the 

hotter the object, the shorter the wavelength. 

TNT (Trinitrotoluene) – Useful explosive material with convenient handling properties.

TNT Equivalent Weight – The weight of TNT which would produce an explosion of 

equal magnitude as a unit mass of the hazardous substance under pressure.
24 CFR Part 51 Subpart C Barrier Design Guidance

10

VI - Units of Measure

The following are the units of measure used throughout this guidance:

Area

Unit of measure Abbreviation

Square foot ft2

Density

Unit of measure Abbreviation

Kilogram per cubic meter kg/m3

Heat of Combustion

Unit of measure Abbreviation

Kilocalories/Kilogram kcal/kg

MegaJoules/Kilogram MJ/kg

Heat Emissivity 

Unit of measure Abbreviation

British Thermal Unit per square foot per hour BTU/ft2-hr

Kilowatt per square meter kw/m2

Length

Unit of measure Abbreviation

Meter m

Centimeter cm

Kilometer km

Inch in

Foot ft

Mile mi

Mass

Unit of measure Abbreviation

Kilogram kg

Pressure

Unit of measure Abbreviation

Pounds per square inch psi
24 CFR Part 51 Subpart C Barrier Design Guidance

11

Volume

Unit of measure Abbreviation

Cubic Meter m

3

Cubic Centimeter cm

3

Cubic Inch in

3

Cubic Foot ft

3

Ounce oz

Pint pt

Quart qt

Liter li

U.S Gallon gal

British Imperial Gallon Imp gal

Weight

Unit of measure Abbreviation

Pounds lbs
24 CFR Part 51 Subpart C Barrier Design Guidance

12

VII – Basic Mitigation Principles

Why is mitigation required? - Mitigation is required to protect the buildings and the 

people that will perform activities related to the proposed HUD-assisted project site 

locations. This applies whether the HUD-assisted project is intended for residential, 

recreational, institutional or commercial use. 

When is mitigation required? - When the ASD is not achievable between the hazard and 

the proposed site for development, and no suitable site is available.

If the ASD is achievable, mitigation is not required.

(The requirement for achieving the ASD or using mitigation applies only to HUD-assisted 

projects close to specific stationary, hazardous operations which store, manage, or 

process materials of an explosive or flammable nature.)
24 CFR Part 51 Subpart C Barrier Design Guidance

13

VIII – Basic Barrier Principles

When is a barrier required? – If the ASD from a facility that processes, stores or 

manufactures substances of explosive or fire prone nature (hazardous facility) cannot be 

achieved for a proposed HUD-assisted project based on the following departmental 

standards:

Thermal Radiation 

o Structures - 10,000 BTU/ft2-hr; 

o People – 450 BTU/ft2-hr

Blast Overpressure 

o Structures - 0.5 psi

And there are no natural or man-made barriers in between the proposed HUD-assisted 

project and the hazardous facility of adequate size and strength that can shield the 

proposed HUD-assisted project from the hazardous facility,

The following mitigation options are suggested:

Bury the hazard – Often a less expensive alternative to building a mitigation 

barrier.

Modify the building design to compensate for the ASD - The building design can 

be modified by using heat retardant and high tensile strength materials in the 

direction where the hazardous facility is located, to compensate for the ASD. 

Buildings can also be re-arranged and their exteriors shapes modified. A 

combination of these approaches may be used to provide an acceptable level of 

protection, e.g., a horseshoe-shaped building oriented with the convex curve 

facing the hazard and the structure augmented with heat retardant and tensile 

strength materials.

Choose another site

Lastly, you can resort to a barrier.

How does a barrier work/what does it do? - A barrier works as abatement for thermal 

heat flux and blast overpressure and provides protection to HUD-assisted projects when 

the ASD is not achievable. 

Depending on the hazard being studied, the barrier can be designed to withstand the 

following:

o Blast Overpressure 

o Thermal Heat Flux

o Or both

Based on the thermal heat flux emitted from combustion of a flammable product or the 

peak positive incident pressure (blast overpressure) from a containerized product under 

pressure (if the product is chemically unbalanced and explodes with high energy), a

barrier can be designed and implemented to protect the HUD-assisted project.
24 CFR Part 51 Subpart C Barrier Design Guidance

14

Who should design a barrier? - Only a licensed professional (e.g., civil or structural 

engineer) should design and oversee the construction of mitigation barriers.

What information is needed for the design of barriers for mitigation? -

For sites involving projects with blast overpressure conditions – Peak positive incident 

pressure

For sites involving projects with thermal heat flux conditions – Thermal heat flux value
24 CFR Part 51 Subpart C Barrier Design Guidance

15

IX – Guidelines for the Users of this Document

This section is based on a site mitigation analysis, to provide users with a basic

guideline using questions (a-e), related to the HUD-assisted project site. Based on the 

results of the site mitigation analysis, the required information can be provided to the 

licensed professional engineers (civil or structural) for a barrier to be designed and 

implemented to provide the required level of protection for the proposed HUD-assisted

project site.

Mitigation analysis questions for the proposed site:

a) Has the Acceptable Separation Distance (ASD) been calculated?

If the ASD has not been calculated, then

o Calculate the ASD – The ASD is the first step towards mitigation analysis for 

HUD-assisted projects near hazardous operations that store, handle or 

process fire-prone or explosive materials.

If the ASD has been calculated, two results are possible:

The ASD is achievable using the proposed site - No further action required

The ASD is not achievable using the proposed site – Mitigation may be 

required

b) The ASD has been calculated for the proposed HUD-assisted project site 

and it is not achievable. Do natural or man-made barriers exist between the 

proposed HUD-assisted project and the hazard?

Natural barriers are hills, mountains, earthen elevations, etc.

Man made barriers are buildings, housing developments and other structures.

Natural or man-made barriers may serve as abatement from thermal heat flux 

or blast overpressure effects that can impact HUD-assisted projects and the 

people who will perform activities associated with the respective projects.

If there are natural or man-made barriers between the proposed HUD-assisted 

project site and the hazard, will the available barrier serve as abatement from 

the potential effects (thermal heat flux, blast overpressure or both) of the 

hazard?

The following points provide valuable information to evaluate the available 

barrier between the proposed HUD-assisted project and the hazard:

o Man-made or natural barriers may serve as abatement from thermal heat flux or 

blast overpressure effects that can impact HUD-assisted projects and the people 

that will perform activities associated with the respective projects.

o If the ASD is not achievable between the proposed HUD-assisted project 

site and the hazardous operation/facility, but there is not a clear line of 

sight between the proposed HUD-assisted project site and the hazard,
24 CFR Part 51 Subpart C Barrier Design Guidance

16

mitigation may not be required. Under the regulation 24 CFR Part 51

Subpart C, if there is natural or man made abatement in between the 

proposed HUD-assisted project site and the studied hazard site, impeding 

a clear view from the proposed HUD-assisted project site to the hazard 

site, the abatement might serve as mitigation for the proposed HUDassisted project.

 If it has been determined that mitigation may not be required using 

the above mentioned analysis, the natural or man made 

abatement must be further analyzed to ensure it will provide an 

acceptable level of protection for the proposed HUD-assisted 

project site. Only a licensed professional engineer (civil or 

structural) should analyze and confirm the acceptability of 

preexisting barriers, based on the hazard being analyzed.

o If the ASD is not achievable between the site to be developed and the 

hazard operation/facility and there is a clear line of sight between the 

proposed HUD-assisted project site and the hazard operation, mitigation 

is required.

c) There are natural or man-made barriers between the HUD-assisted project

site and the hazard. How can it be determined if the natural or man-made 

barriers in between the proposed HUD-assisted project site and the hazard are 

of adequate size and strength that can shield the proposed HUD-assisted 

project from the hazard?

Determining if the natural or man-made barriers are of adequate strength and 

size is done by calculating the peak positive incident pressure (blast 

overpressure) for a containerized product under pressure (if the product is 

chemically unbalanced and explodes with high energy) or the thermal heat flux 

(heat emissivity) from combustion of a flammable product.

Natural and man-made barriers are analyzd for structural strength, based on the 

thermal heat flux, peak positive incident pressure or both, emitted from the 

hazard. 

Only a licensed professional engineer (civil or structural) is qualified to analyze a natural 

or a man-made barrier for structural strength under the following scenarios:

An existent natural or man-made barrier is located between a hazard and a HUDassisted project site, or

A barrier must be designed, constructed and implemented between a hazard and 

a HUD-assisted project site

The thermal heat flux and/or the peak positive incident pressure values must be 

calculated for a complete analysis or design of mitigation barriers. Only a licensed 

professional engineer (civil or structural) should design and oversee the construction of 

mitigation barriers. For questions or concerns calculating the thermal heat flux or 

the peak positive incident values on the analysis or design of mitigation barriers, 

please contact Headquarters (Office of Environment and Energy, Nelson A. Rivera –

202-402-4455).
24 CFR Part 51 Subpart C Barrier Design Guidance

17

Flowchart illustrating a mitigation analysis for a proposed HUD-assisted project

site

Mitigation 

Analysis

24 CFR 

51C

(Start)

ASD achievable 

for proposed 

HUD-assisted 

project site from 

the hazard site ?

Existent natural 

or man-made 

barriers between 

the proposed 

HUD-assisted 

project site and 

the hazard site ?

Can the hazard 

site be seen 

from the 

proposed 

HUD-assisted 

project site ?

No further action 

required (Stop) Suggested 

Mitigation 

Options:

1. Bury the 

hazard

2. Modify the 

building 

design to 

compensate 

for the ASD

3. Choose 

another site

4. Resort to a 

barrier

Natural or man 

made barrier of 

adequate size 

and strength to 

shield the 

proposed HUDassisted project?

(Only a licensed 

professional 

engineer (civil or 

a structural) can 

make this 

determination)

Is a Barrier 

required for the 

proposal ?

Provide this guidance to the licensed 

professional for calculation of the 

required barrier design criteria, based on 

the Regulation standards of blast 

overpressure and thermal radiation. 

Apply one of 

the 

suggested 

mitigation 

options other 

than barriers

Yes

No Yes

No

No

Yes

No

Yes

Yes

No
24 CFR Part 51 Subpart C Barrier Design Guidance

18

Calculation of the Thermal Heat Flux (Q)

 

For inquiries involving thermal radiation emitted from a hazard, the natural or man-made 

barrier must be analyzed or designed for the amount of heat the barrier can withstand 

from the hazard. This heat is known as the thermal heat flux. The thermal heat flux is the 

heat from combustion emitted from the hazard. 

A mathematical formula for the determination of the thermal heat flux emitted from a 

hazard is as follows:

Formula #1: Q = [828x(Mass of Vapor of Substance being Assessed (kg))

0.771]/[Standoff

Distance(meter)]2

Note: “x” means multiply; “/” means divide

The following formula is used to determine the mass of vapor of the substance being 

assessed, emitted from the hazard’s container:

Formula #1.1: Mass of Vapor of the Substance being Assessed = Volume of Vapor of 

the Substance being Assessed (m3) x Substance Vapor Density (kg/m3)

Where,

Volume of Vapor of the Substance being assessed = [Volume of Container being

Assessed x 0.15] (m3)

Note: the ratio of 0.15 means the percentage of vapor content in a container with a 

liquid–gas (vapor) mixture contained under pressure. 

Section XIII of this guidance includes a table with fuel vapor density values for most 

common hydrocarbon fuels used in industry. 

Formula #1.2: Standoff Distance = [(Fire ball flame height (m))2+ (Distance at ground 

level from the origin (m))2]

0.5

Distance at ground level from the origin (m) = distance from the closest point on the 

perimeter of the container being assessed to either of the following:

the closest point on the perimeter of the proposed HUD-assisted 

project site or 

the area where a fire barrier can be implemented. 

Formula #1.2a: Fire ball flame height = 12.73 x (Volume of Vapor of the substance 

being assessed (m3))

1/3

.
24 CFR Part 51 Subpart C Barrier Design Guidance

19

Table I: Volume conversion

The following table provides unit conversion factors for volume calculation

The actual number of a type of unit in the first column should be multiplied by the 

appropriate factor to convert to the indicated type of unit in the succeeding columns

meter3centimeter3liter foot3inch3

cubic

meters

1 1061000 35.31 6.102x104

cubic 

centimeters

10-61 10-33.531x10-56.102x10-2

liters 10-3

1000 1 3.531x10-261.02

cubic feet 2.832x10-2

2.832x10428.32 1 1728

cubic 

inches

1.639x10-516.39 1.639x10-25.787x10-41

1 U.S. fluid gallon = 4 U.S. fluid quarts = 8 U.S. fluid pints = 128 U.S. fluid ounces = 231 

in3

1 British imperial gallon = 277.4 in3

1 liter = 10-3 m

3

HINT: To change from gallons to m3(cubic meters), multiply the amount of gallons 

(volume) by the quantity 1.6387x10-5times 231.

This is: Given [volume in gallons] x (1.6387x10-5) x 231
24 CFR Part 51 Subpart C Barrier Design Guidance

20

Step 1: 

o The mass of vapor of the substance being assessed can be 

calculated by using Formula # 1.1.

o The volume of vapor of the substance being assessed can be 

calculated by multiplying the volume of the container being

assessed by 0.15. 

o Formula # 1.1 requires the volume of vapor of the substance 

being assessed to be expressed in units of cubic meters.

o Table I and the information following it provide unit conversion 

factors for container volume calculation. 

o Section XIII of this guidance includes a table with fuel vapor 

density values for most common hydrocarbon fuels used in 

industry. 

Step 2: 

o Calculate the standoff distance. The standoff distance is calculated by using 

Formula #1.2 and Formula #1.2a.

The following notes are for standoff distance determination:

Notes: 

o When there are two or more containers of the same size, the thermal 

heat flux needs to be evaluated for the container with the closest 

standoff distance to the site.

o When two containers of different sizes expose a site and the larger 

container is closer to the site, the thermal heat flux is evaluated only 

for the larger container.

o When two of the same kind of containers of different size are exposed 

to a site and the smaller container is closer to the site, the thermal 

heat flux needs to be evaluated for both containers.

Formula #1 requires the standoff distance to be expressed in units of meters (m). 

Steps providing clarification for the determination of the following

properties from a substance being assessed (hazard):

Mass of vapor 

Volume of vapor

Vapor density 

Thermal heat flux 
24 CFR Part 51 Subpart C Barrier Design Guidance

21

Table II: Length conversion

The following table provides unit conversion factors for length calculation

The actual number of a type of unit in the first column should be multiplied by the 

appropriate factor to convert to the indicated type of unit in the succeeding columns.

centimeters meters kilometers inches feet miles

centimeters 1 10-2

10-50.3937 3.281x10-

2

6.214x10-6

meters 100 1 10-3

39.37 3.281 6.214x10-4

kilometers 105

1000 1 3.937x1043281 0.6214

inches 2.540 2.54x10-2

2.54x10-51 8.33x10-21.57x10-5

feet 30.48 0.3048 3.04x10-4

12 1 1.89x10-4

miles 1.60x105

1609 1.609 6.33x1045280 1

Step 3: 

o Calculate the thermal heat flux by inserting the values previously determined 

for the mass of vapor of the substance being assessed and the standoff 

distance into Formula #1.

HINT: The thermal heat flux value provided by Formula #1 is expressed in kw/m2

(Kilowatt/square meter) units. To convert this value into BTU/ft2-hr (British 

Thermal Unit/square foot-hr) units, multiply the kw/m2result by 317.0781.
24 CFR Part 51 Subpart C Barrier Design Guidance

22

Flowchart illustrating Thermal Heat Flux calculation procedures for a hazard

Thermal Heat 

Flux calculation 

procedures

24CFR 51C

(Start)

Step #1:

Calculate the mass of vapor for the 

substance being assessed (hazard):

Use Formula #1.1

Step #2:

Calculate the standoff distance

Use Formulas #1.2 and 1.2a

Step #3:

Calculate the Thermal Heat Flux

Insert calculated values of mass 

of vapor of the substance being 

assessed and the standoff 

distance into Formula #1

Calculation procedure 

complete (Stop)
24 CFR Part 51 Subpart C Barrier Design Guidance

23

o Calculation of the peak positive incident pressure (Ps)

For inquiries involving blast overpressures emitted from a hazard, the natural or man 

made barrier must be analyzed or designed for structural strength sufficient for the 

pressure the barrier may experience from the hazard. This pressure is known as the 

peak positive incident pressure. The peak positive incident pressure is the pressure 

emitted from a hazard’s pressure wave after an explosion has occurred. 

A mathematical formula for the determination of this pressure is as follows: 

Formula #2: Z = Scaled Distance = R/(W)1/3

Where, 

R= Standoff distance (ft) between the explosive hazard and the proposed HUD-assisted 

project site. The distance is measured from the center of the largest capacity container 

to the proposed HUD-assisted project site or the area where a blast barrier can be 

implemented.

W= TNT equivalent weight of the hazard being analyzed/studied

Below is a visual representation of a hazard (TNT equivalent weight – W) and the 

standoff distance (R) between the hazard and a structure
24 CFR Part 51 Subpart C Barrier Design Guidance

24

 Formula #3: TNT equivalent weight = W = Mc x (Hc/1155) x Y

 Where,

Mc = mass of the substance (hazard) being assessed (kg)

Hc = heat of combustion of the substance (hazard) being assessed (kcal/kg),

Y = yield factor (the fraction of the mass of the substance (hazard) that contributes to 

the explosion). 
24 CFR Part 51 Subpart C Barrier Design Guidance

25

Step 1:

o The TNT equivalent weight for the substance being assessed

(hazard) can be calculated by using Formula #3.

Where, 

Mc = mass of the chemical (hazard) being analyzed, in kilograms

 Density = Mass/Volume, expressed in kilograms per cubic 

meter (kg/m3)

Mass = Density x Volume, expressed in 

kilograms

Mc = Density of the chemical (hazard being analyzed) multiplied by 

the Volume of the container.

 

Section XI of this guidance includes a table with density values for 

the most common hazardous and non-hazardous (for reference)

substances used in industry.

Formula #3 requires container volume to be expressed in units of 

cubic meters (m3).

Table I provides unit conversion factors for container volume 

calculation.

If the container volume is provided in gallons, multiply the amount of 

gallons by 1.6387x10-5times 231 to convert gallons to cubic meters. 

This is: Given [volume in gallons] x (1.6387x10-5) x 231

Step 1a – The heat of combustion (Hc) for most common fuels and 

organic compounds can be obtained from Section XII of this guidance in 

unit values of Mega Joules per kilogram (MJ/kg).

 Formula #3 requires the heat of combustion to be 

expressed in units of kilocalories per kilogram (kcal/kg).

Steps providing clarification for the determination of the following properties 

from a substance being assessed (hazard):

o TNT equivalent weight 

o Scaled distance

o Peak positive incident pressure
24 CFR Part 51 Subpart C Barrier Design Guidance

26

 To perform this unit change, multiply the Mega Joules 

per kilogram value by 238.8 to obtain a value in units of 

kilocalories per kilogram (kcal/kg).

Step 1b – Assign a value of 0.02 to the yield factor (Y). The yield factor is 

the fraction of the mass of a substance being assessed (hazard) that 

contributes to the explosion.

Step 1c - The values of Mc (mass of a substance being assessed

(hazard)), Hc (heat of combustion of a substance being assessed), and Y 

(yield factor) are used in Formula #3 to calculate the equivalent weight of 

TNT (W).

Step 2 – Calculate the standoff distance (R). The standoff distance is measured 

from the center of the container (hazard) being assessed to the closest point of 

the perimeter of the proposed HUD-assisted project site or the area where a 

blast barrier can be implemented. 

HINT: Always measure from the closest point of the perimeter.

The following notes are for standoff distance determination:

Notes: 

o When there are two or more containers of the same size, the 

peak positive incident pressure needs to be evaluated for the 

container with the closest standoff distance to the site.

o When two containers of different sizes expose a site and the 

larger container is closer to the site, the peak positive incident 

pressure needs to be evaluated only for the larger container.

o When two of the same kind of containers of different size are

exposed to a site and a smaller container is closer to the site, 

the peak positive incident pressure needs to be evaluated for 

both containers.

Formula #2 requires the standoff distance to be expressed in units of feet (ft). 

Table 2 provides unit conversion factors for length calculation.

Step 3 - Once the standoff distance (R) has been determined, the scaled 

distance (Z) can be calculated by inserting the values of R and W (equivalent 

weight of TNT) in Formula #2.
24 CFR Part 51 Subpart C Barrier Design Guidance

27

Step 4 – Once the scaled distance has been calculated, the value can be plotted 

in the following graph for the determination of the peak positive incident pressure

(Ps).
24 CFR Part 51 Subpart C Barrier Design Guidance

28

Flowchart illustrating Peak Positive Incident Pressure calculation procedures for a 

hazard

Peak Positive Incident 

Pressure calculation 

procedures

24 CFR 51C

(Start)

Step #1:

Calculate the mass of the substance being 

assessed (Mc) = Density x Volume

o Step #1a – Calculate the 

Heat of Combustion (Hc). 

Section XII of this 

guidance provides Hc

values for most common 

fuels and organic 

compounds 

o Step #1b – Assign a value 

of 0.2 for the Yield Factor 

(Y)

o Step #1c – Insert calculated 

values of Mc, Hc and Y into 

Formula #3 to calculate the 

Equivalent Weight of TNT 

(W)

Step #2:

Calculate the Standoff Distance (R) – Measured 

from the center of the container (hazard) being 

assessed to the perimeter of the proposed HUDassisted project site or the area where a blast 

barrier can be implemented 

Step #3:

Calculate the Scaled Distance (Z), by inserting the 

calculated values of R and W into Formula #2

Step #4

Plot the Scaled Distance (Z) value onto the Peak 

Positive Incident Pressure (Ps) graph for 

determination of the (Ps)

Calculation procedure 

complete (Stop)
24 CFR Part 51 Subpart C Barrier Design Guidance

29

d. If there are no natural or man made barriers between the HUD proposed 

project site and the hazard and the last resort is to design and implement a 

barrier, 

What information must be known and provided to the structural engineer 

for the design of the subject barrier?

For inquiries regarding the design and implementation of barriers, the following 

site information is required:

o A project layout map (for better analysis of the hazard(s) in 

relation to the proposed HUD-assisted project location)

o Site map (preferably a topographic map with elevations)

 Digitized topographic maps:

Free digital topographic maps for general public 

use are available from the following sources:

o Yahoo maps, 

http://developer.yahoo.com/maps/

o Google Earth, http://earth.google.com/

Note: HUD does not endorse any of the referenced 

electronic sources of information

 Address of the HUD-assisted project and the facility 

with the hazard(s)

o Using the site map, and a mile as a radius parameter distance, plot a 

perimeter from the center of the proposed HUD-assisted project site, to 

delineate a project boundary where facilities inside that boundary that 

store, manufacture or process substances of explosive or fire prone 

nature must be evaluated for ASD determination

Within those identified facilities, if there are 

containers for storage of chemicals of fire prone 

or explosive nature, identify and list the 

following characteristics for each container:

o Chemical name (not the trade name).

o Type (above ground only) and size 

(volume capacity in gallons) of each of 

the containers on site.

o If containers are diked or undiked. If 

diked, provide the dike area in square 

feet. 

o If containers are storing pressurized (gases) or 

unpressurized (liquids) substances.

o Standoff distance for calculation of the peak 

positive incident pressure or thermal heat flux.
24 CFR Part 51 Subpart C Barrier Design Guidance

30

d.1. For stationary containers, storing substances under pressure of 

explosive nature (fire may or may not be an additional product of the 

explosion, depending on the flammability of the substance being 

assessed)

What information is required to be provided to the structural engineer 

for the design and implementation of a blast barrier? 

The peak positive incident pressure

Once the peak positive incident pressure has been calculated, a structural 

engineer can design and implement a blast barrier to withstand that peak 

positive incident pressure emitted from a hazard.

What information is required to be provided to the structural engineer 

for the design and implementation of a fire barrier (if the substance 

being assessed has flammable properties)?

The thermal heat flux 

The thermal heat flux is the heat from combustion emitted from a hazard 

Once the thermal heat flux has been calculated, a structural engineer can 

design and implement a fire barrier to withstand that thermal heat flux.

d.2. For stationary containers, storing substances not under pressure of 

fire-prone nature, what procedure should be followed to address the 

required information to be provided to the structural engineer for the 

design and implementation of a fire barrier?

1. To calculate the thermal heat flux (Q),from substances bearing the specified 

conditions as stated in d.2, please contact Headquarters (Office of Environment and 

Energy, Nelson A. Rivera – 202-402-4455). The thermal heat flux effects on the 

proposal need to be calculated on a case by case basis, and depending on the 

results of the analysis, if a fire mitigation wall is required it may not be feasible for the 

developer due to the size requirements to mitigate the fire ball produced by the 

hazard. 
24 CFR Part 51 Subpart C Barrier Design Guidance

31

e. Has the project been rejected or have mitigation options other than 

barrier construction (e.g., the hazard will be buried) been identified?

If the project has been rejected – no further 

action is required

If the hazard will be buried – no further action is 

required

If another site, that does not have hazards, will 

be used to meet the project goal – no further 

action is required
24 CFR Part 51 Subpart C Barrier Design Guidance

32

X - Mitigation Example:

Site information:

Calculate the peak positive incident pressure (Ps) from a 1000 gallon container of liquid 

propane gas, at 3 ft, 9 ft, 50ft and 100ft distance, for a HUD housing development that is 

planned to be built at 50 ft from the subject container. 

Note: Barriers should be constructed as close to the hazard source as possible. In this

example, we are calculating the peak positive incident pressure (Ps) at various distances 

from the hazard to demonstrate that the Ps value decreases depending on how far this

pressure is measured from the hazard. In this example, the barrier will be designed at 3 

ft from the hazard.

Since the barrier will be implemented at 3 ft from the hazard and propane gas can 

produce blast overpressure and thermal radiation, we also must calculate the thermal 

heat flux (Q) at 3 ft from the subject container.

There are no man made or natural barriers between the location of the HUD project site 

and the hazard (container). There is a clear line of sight from the hazard to the location 

of the proposed HUD site for a housing development.

Site mitigation analysis:

In accordance with Worksheet # 4, located at page 12 of the HUD ASD Guidance, 

(Siting of HUD-Assisted Projects Near Hazardous Facilities) the Acceptable Separation 

Distance for blast overpressure for the container of this example is 220 ft. 

In accordance with Worksheet # 3, located at page 11 of the HUD Guidance (Siting of 

HUD-Assisted Projects Near Hazardous Facilities) the Acceptable Separation Distance 

for thermal radiation for the container of this example is 50 feet for buildings and 275 for 

people.

The location for the proposed HUD site for development meets the department’s 

acceptable separation distance requirement for thermal heat flux for buildings but not for 

people.

The location for the proposed HUD site for development does not meet the department’s

acceptable separation distance requirement for blast overpressure for buildings.

The location for the proposed site does not allow a new building design configuration for 

protection of the building occupants from the heat or blast overpressure emitted from the 

hazard, there are no natural or man-made barriers between the hazard and the location 

of the HUD proposed site and because of environmental regulations, the container 

(hazard) cannot be buried. 

As a last resort, if a barrier was to be designed and implemented between the hazard 

and the location of the HUD proposed site for development, the thermal heat flux (from 

the heat of combustion emitted from the hazard) and the peak positive incident pressure 
24 CFR Part 51 Subpart C Barrier Design Guidance

33

(blast overpressure) are required to be provided to the structural engineer, for the 

protection of the people and buildings related to the HUD-assisted project.

Peak Positive Incident Pressure Calculation:

Substance being assessed = Liquid Propane Gas

The density of propane in liquid form is 493.53 Kg/m3– Section XI of this guidance

The container with liquid propane gas has a volume of 1000 gallons. Such volume in 

units of m3(cubic meters) is 3.7854.

To change from gallons to cubic meters:

(1000 x 1.6387x10-5x 231)

Density = mass / volume 

Mass = density x volume 

Mass of chemical being analyzed (Mc) = 493.53 x 3.7854 = 1,868.20 kg 

Heat of combustion for propane = Hc (For liquid propane gas) = 46.357 MJ/kg – Section 

XII of this guidance. 

Heat of combustion for propane changed from MegaJoules/kilograms (MJ/kg) into 

kilocalories/kilograms (kcal/kg) = 46.357 MJ/kg = 11,070 kcal/kg

To change from MegaJoules/kilograms to kilocalories/kilograms:

(46.357 x 238.8) 

Y is the yield factor (the fraction of the mass of chemical that contributes to the 

explosion, which is 0.02 for fuel gas explosions)

The values of Mc, Hc and Y are used in Formula #3 to calculate the equivalent weight of 

TNT (W) as follows:

W = 1,868.20 x (11,070/1155) x 0.02 

W = 358.11 Lbs

The following are the standoff distances (R) where the scaled distances will be 

calculated:

At 3 feet, 9 feet, 50 feet and 100 feet

The scale distances (Z) can be determined by using the previous stated standoff 

distances in Formula #2 as follows:
24 CFR Part 51 Subpart C Barrier Design Guidance

34

At 3 feet standoff distance: Z = R/(W)1/3 = 3/(358.11)

1/3 

= 0.423

At 9 feet standoff distance: Z = 9/(358.11)1/3 = 1.27

At 50 feet standoff distance: Z = 50/(358.11)

1/3

= 7.04

At 100 feet standoff distance: Z = 100/(358.11)

1/3 = 14.08

Once the scaled distances have been calculated, the values are plotted in the following 

graph for the determination of the peak positive incident pressures (Ps)

The peak positive incident pressures (Ps) are as follow:

At 3 feet standoff distance: Z = 0.423, the Ps = 2,800 psi

At 9 feet standoff distance: Z = 1.27, the Ps = 800 psi

At 50 feet standoff distance: Z = 7.04, the Ps = 15 psi

At 100 feet standoff distance: Z = 14.08, the Ps = 5.6 psi
24 CFR Part 51 Subpart C Barrier Design Guidance

35

The substance being assessed (propane gas) poses the following hazards:

Blast overpressure (calculated for a barrier design specification as the peak 

positive incident pressure)

Thermal radiation (calculated for a barrier design specification as the thermal 

heat flux) 

The thermal heat flux at 3 ft from the hazard (liquid propane gas container) can be 

calculated as follows:

The vapor density of propane is 1.60 kg/m3– Section XIII of this guidance

Volume of liquid propane vapor = Volume of container where the liquid propane is stored

= 1,000 gallons x 0.15 = 150 gallons = 0.5678 m

3

To change from gallons to cubic meters:

(150 x (1.6387x10-5) x 231)

Using Formula #1.1,

Mass of Vapor of the Substance being Assessed = Volume of Vapor of the Substance 

being Assessed x Substance vapor density (kg/m3)

Mass of vapor of liquid propane = 0.5678 x 1.60 = 0.9085 kg

Using Formula #1.2a, 

Fire ball flame height = 12.73 x (Volume of liquid propane vapor (m3))1/3

Fire ball flame height = 12.73 x 0.56781/3 = 10.54 m

The distance at ground level to the origin = 3 feet = 0.9144 m

To change from feet to meters:

(3 x 0.3048)

Using Formula #1.2,

Standoff Distance = [(Fire ball flame height) (m))2+ (Distance at ground level to the 

origin (m))2]

0.5

Standoff Distance = [10.542+ 0.91442]

0.5

= 10.58 m

By inserting the calculated values of the mass vapor of liquid propane and the standoff 

distance into Formula #1,

Thermal Heat Flux = Q = (828 x (mass of vapor of liquid propane)

0.771) / (Standoff 

distance)2
24 CFR Part 51 Subpart C Barrier Design Guidance

36

Q = (828 x 0.90850.771) / (10.58)

2

= 6.87 kw/m2= 2,178.18 BTU/ft2-hr 

To change from kw/m2to BTU/ft2-hr:

(6.87 x 317.0781) 

Suggested design criteria for a barrier, to be provided to the structural engineer, would 

be as follows:

“A barrier, made out of a material to withstand a calculated thermal heat flux of 2,178.18

BTU/ft2-hr and peak positive incident pressure of 2,800 psi must be designed and 

implemented between the hazard and the proposed project, shielding all points of the 

project, from line of sight exposure to the container (hazard), so the subject hazard can 

be appropriately mitigated.” 
24 CFR Part 51 Subpart C Barrier Design Guidance

37

XI - The following table provides the density of most common hazardous and not 

hazardous substances including fuels. The table does not include the “universe” 

of substances, but it includes the most used in industry.

Liquid Temperature (Degrees C) Density (kg/cubic meter)

1,1,2-

Trichlorotrifluoroethane

25 1564

1,2,4- Trichlorobenzene 20 1454

1,4 - Dioxane 20 1033.60

2-Methoxyethanol 20 964.60

Acetic Acid 25 1049.10

Acetone 25 784.58

Acetonitrile 20 782.20

Alcohol, ethyl 25 785.06

Alcohol, methyl 25 786.51

Alcohol, propyl 25 799.96

Ammonia (aqua) 25 823.35

Analine 25 1018.93

Automobile oils 15 880-940

Beer (varies) 10 1010

Benzene 25 873.81

Benzil 25 1079.64

Brine 15 1230

Bromine 25 3120.40

Butyric Acid 20 959

Butane 25 599.09

n-Butyl Acetate 20 879.60

n-Butyl Alcohol 20 809.70

n-Butyl Chloride 20 886.20

Caproic Acid 25 921.06

Carbolic Acid 15 956.30

Carbon disulfide 25 1260.97

Carbon tetrachloride 25 1584.39

Carene 25 856.99

Castor oil 25 956.14

Chloride 25 1559.88

Chlorobenzene 20 1105.80

Chloroform 20 1489.20

Chloroform 25 1464.73

Citric Acid 25 1659.51

Coconut oil 15 924.27

Cotton seed oil 15 925.87

Cresol 25 1023.58

Creosote 15 1066.83

Crude Oil, 48degrees API 60F 790

Crude Oil, 40degrees API 60F 825

Crude Oil, 35.6degrees API 60F 847

Crude Oil, 32.6degrees API 60F 862

Crude Oil, California 60F 915
24 CFR Part 51 Subpart C Barrier Design Guidance

38

Crude Oil, Mexican 60F 973

Crude Oil, Texas 60F 873

Cumene 25 860.19

Cyclohexane 20 778.50

Cyclopentane 20 745.40

Decane 25 726.28

Diesel Fuel 20 to 60 15 820-950

Diethyl ether 20 714

o-Dichlorobenzene 20 1305.80

Dichloromethane 20 1326.00

Diethylene glycol 15 1120

Dichloromethane 20 1326.00

Dimethyl Acetamide 20 941.50

N,N-Dimethylformamide 20 948.70

Dimethyl Sulfoxide 20 1100.40

Dodecane 25 754.63

Ethane -89 570.26

Ether 25 72.72

Ethylamine 16 680.78

Ethyl Acetate 20 900.60

Ethyl Alcohol 20 789.20

Ethyl Ether 20 713.30

Ethylene Dichloride 20 1253.00

Ethylene glycol 25 1096.78

Fluorine refrigerant R-12 25 1310.95

Formaldehyde 45 812.14

Formic acid 10% 

concentration

20 1025

Formic acid 80% 

concentration

20 1221

Freon 11 21 1490

Freon 21 21 1370

Fuel oil 60 890.13

Furan 25 1416.03

Furforol 25 1154.93

Gasoline, natural 60 711.22

Gasoline, Vehicle 60 737.22

Gas oils 60 890

Glucose 60 1350-1440

Glycerin 25 1259.37

Glyme 20 869.10

Glycerol 25 1126.10

Heptane 25 679.10

Hexane 25 654.83

Hexanol 25 810.53

Hexene 25 671.17

Hydrazine 25 794.52

Iodine 25 4927.28

Ionene 25 932.27
24 CFR Part 51 Subpart C Barrier Design Guidance

39

Isobutyl Alcohol 20 801.60

Iso-Octane 20 691.90

Isopropyl Myristate 20 853.20

Kerosene 60 817.15

Linolenic Acid 25 898.64

Linseed oil 25 929.07

Methane -164 464.54

Methanol 20 791.30

Methyl Isoamyl Ketone 20 888.00

Methyl Isobutyl Ketone 20 800.80

Methyl n-Propyl Ketone 20 808.20

Methyl t-Butyl Ether 20 740.50

N-Methylpyrrolidone 20 1030.40

Methyl Ethyl Ketone (MEK) 20 804.90

MEK 25 802.52

Milk 15 1020-1050

Naphtha 15 664.77

Naphtha, Wood 25 959.51

Napthalene 25 820.15

Ocimene 25 797.72

Octane 15 917.86

Olive oil 20 800-920

Oxygen (liquid) -183 1140

Palmitic Acid 25 850.58

Pentane 20 626.20

Pentane 25 624.82

Petroleum Ether 20 640.00

Petrol, natural 60 711.22

Petrol, Vehicle 60 737.22

Phenol 25 1072.28

Phosgene 0 1377.59

Phytadiene 25 823.35

Pinene 25 856.99

Propane -40 583.07

Propane, R-290 25 493.53

Propanol 25 804.13

Propylene Carbonate 20 1200.60

Propylene 25 514.35

n-Propyl Alcohol 20 803.70

Propylene glycol 25 965.27

Pyridine 25 978.73

Pyrrole 25 965.91

Rape seed oil 20 920

Resorcinol 25 1268.66

Rosin oil 15 980

Sabiname 25 812.14

Sea water 25 1025.18

Silane 25 717.63

Sodium Hydroxide(caustic 15 1250
24 CFR Part 51 Subpart C Barrier Design Guidance

40

soda)

Sorbaldehyde 25 895.43

Soya bean oil 15 924-928

Stearic Acid 25 890.63

Sulphuric Acid 95% 20 1839

Sunflower oil 20 920

Styrene 25 903.44

Terpinene 25 847.38

Tetrahydrofuran 20 888.00

Toluene 20 866.90

Toluene 25 862.27

Triethylamine 20 727.60

Trifluoroacetic Acid 20 1489.00

Turpentine 25 868.20

Water, pure 4 1000.00

Water , sea 77 1021.98

Whale oil 15 925

o-Xylene 20 880.20
24 CFR Part 51 Subpart C Barrier Design Guidance

41

XII – The following table provides the heat of combustion for common fuels and 

for some organic compounds

Heat of Combustion (MJ/kg)

Fuels MJ/kg

Hydrogen 120.971

Gasoline 47

Diesel 45

Ethanol 28.865

Propane 46.357

Butane 45.752

Wood 15

Coal 15-27

Natural Gas 54

Organic Compounds MJ/kg

Methane 50.009

Ethane 47.794

Pentane 45.357

Hexane 44.752

Heptane 44.566

Octane 44.427

Nonane 44.311

Decane 44.240

Undecane 44.194

Dodecane 44.147

Isobutane 45.613

Isopentane 45.241

2-Methylpentane 44.682

2,3-Dimethylbutane 44.659

2,3-Dimethylpentane 44.496

2,2,4-Trimethylpentane 44.310

Cyclopentane 44.636

Methylcyclopentane 44.636

Cyclohexane 43.450

Methylcyclohexane 43.380

Ethylene 47.195

Propylene 45.799

1-Butene 45.334

cis-2-Butene 45.194

trans-2-Butene 45.124

Isobutene 45.055

1-Pentene 45.031

2-Methyl-1-pentene 44.799

1-Hexene 44.426

1,3-Butadiene 44.613

Isoprene 44.078

Nitromethane 10.513
24 CFR Part 51 Subpart C Barrier Design Guidance

42

Nitropropane 20.693

Acetylene 48.241

Methylacetylene 46.194

1-Butyne 45.590

1-Pentyne 45.217

Benzene 40.170

Toluene 40.589

o-Xylene 40.961

m-Xylene 40.961

p-Xylene 40.798

Ethylbenzene 40.938

1,2,4-Trimethylbenzene 40.984

Propylbenzene 41.193

Cumene 41.217

Methanol 19.937

n-propanol 30.680

Isopropanol 30.447

n-Butanol 33.075

Isobutanol 32.959

Tertiobutanol 32.587

n-Pentanol 34.727

Methoxymethane 28.703

Exoxyethane 33.867

Propoxypropane 36.355

Butoxybutane 37.798

Methanal 17.259

Ethanal 24.156

Propionaldehyde 28.889

Butyraldehyde 31.610

Acetone 28.548

Carbon (graphite) 32.808

Carbon monoxide 10.112

Ammonia 18.646

Sulfur 4.639
24 CFR Part 51 Subpart C Barrier Design Guidance

43

XIII – The following table provides the fuel vapor density for common hydrocarbon 

fuels 

Fuel Vapor Densities (kg/m3)

Fuel kg/m3

Acetone 2

Acetylene 0.90

Benzene 2.80

Butane 2.00

Carbon Monoxide 1.00

Cyclohexane 29.00

Ethanal 1.50

Ethane 1.00

Ethylene 1.00

Gasoline 3.49

Heptane 3.50

Hexane 3.00

Hydrogen 0.10

Methane 0.60

Methanol 1.10

Octene 3.90

Propane 1.60

Propylene 1.50

Styrene 3.60

Toluene 3.10

Xylene 3.70
24 CFR Part 51 Subpart C Barrier Design Guidance

44

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24 CFR Part 51 Subpart C Barrier Design Guidance

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