The types of attacks and data sources that will be considered include external physical assaults, incidents, and accidents. We will start with the type of external physical assaults and attacks.

Weapons

One of the difficulties of protecting a facility from standoff weapons is the range of modern weapons and the damage they can do. The following is generally acknowledged as ranges of the various weapons commonly in use.

Muzzle Energies for Various Cartridges

The projectile fired by a rifle or a handgun, unless it is an explosive round, has a kinetic energy between 1000 and 4000 ft-lb of energy. Many handguns fall into smaller ranges. The kinetic energy delivered drops off somewhat significantly at ranges over 200 m, but that is dependent upon the type of projectile, its weight, and the initial velocity. Table 3.1 indicates the average initial muzzle energy for various types of projectiles commonly found in use. ¹ Wikipedia gives the following information about projectile weapons.

The energy available for a projectile drops off with distance because air resistance slows the projectile. However, at a range of 200 m, the energy available from a rifle shell is between 40 and 70% of the initial muzzle energy. The higher impact energy at 200 yards seems to peak at around 70% when muzzle energy is about 6000 ft-lb. ²

Rifle Grenades

The rifle grenade is generally an antipersonnel weapon that has a maximum range of around 150 m, with a fragmentation or other types of grenade. The fragmentation grenades have an effective shrapnel diameter of between 15 and 20 m. Modern shoulder-launched rifle-type grenades fire a 40 mm cartridge that has an effective range of about 150 m and a maximum range of 400 m. There are a variety of sources of public information on the types of grenades that can be fired from the various launchers, including thermobaric rounds for maximum effect over an area and high-explosive rounds for antitank use. Any of these weapons used against an industrial target would cause a large amount of damage and destruction.

Rocket-Propelled Grenades and Mortars

Rocket-propelled grenades (RPG) are a shoulder-mounted weapon that has a variety of warheads. The warheads can be either high explosive or shaped charge or thermobaric charges. A typical RPG as described by Wikipedia has the following properties:

It is 40–105 millimeters in diameter and weighs between 2.5 and 4.5 kilograms. It is launched by a gunpowder booster charge, giving it an initial speed of 115 meters per second, and creating a cloud of light grey-blue smoke. The rocket motor [2] ignites after 10 meters and sustains flight out to 500 meters at a maximum velocity of 295 meters per second. The grenade is stabilized by two sets of fins that deploy in-flight: one large set on the stabilizer pipe to maintain direction and a smaller front set to induce rotation. The grenade can fly up to 1,100 meters; the fuse sets the maximum range, usually 920 meters.

Fortunately, the accuracy of the weapon is relatively poor. The same article cited earlier suggests that at distances beyond 180 m, the accuracy decreases with increasing distance, especially on a moving target. ³

Modern mortars are high-arc weapons. They are tube fired and muzzle loaded. The diameter and size of the mortar vary between 60 and 120 mm, but there are a number of homemade mortars that are also in use. Because the mortar is fired from the ground in a high arc, it is a plunging weapon, coming into the target from overhead.

The shell fired by a mortar can, depending upon the type of mortar, contain as much as 200 kg of explosives. Larger mortars are usually motor mounted, and the difficulty of carrying multiple high-explosive shells, especially the larger rounds, can limit their applicability. A typical field mortar is the British 81 mm mortar. The system is relatively light in its original configuration; it weighs about 41 kg, but a lighter version is now available. The mortar is crewed by a team of three people and has a range of under 100 m to almost 5900 m. The payload of the mortar is several kilograms of high explosive, but exact information on the payload is not readily available. The accuracy is very good, and at several hundred meters, an experienced crew can drop the mortar round inside a 10 m circle on a consistent basis.

Explosive Energies

The amount of energy available in various types of explosions naturally varies with the explosive compound and the manner in which it is delivered. Explosives are measured in the equivalencies to trinitrotoluene (TNT). One gram of TNT has an energy release of 4162 kcal, although it is often considered as having energy levels between 4100 and 4600 kcal/g. The 4162 kcal/g is a definition roughly equivalent to 23,118,800 ft-lb of energy—per pound of TNT. All explosives are rated in comparison with TNT. Table 3.2 gives a rough conversion for common explosives.

Impact of explosives

The effectiveness of the explosive is in the shock wave it creates. The shock wave creates a rapidly expanding spherical overpressure on all that surrounds it. As the wave expands, it slows and dissipates. The wave generally moves at the speed of sound, and as the wave passes, it can generate a negative pressure wave as the displaced air returns after the shock has passed. This is shown in Figure 3.1.

The timing of the pressure wave is in milliseconds, and the velocity depends upon the power and brisance of the explosive as shown below.

The points for t _A and t _d are influenced by the amount of explosive material and the speed of sound. The calculation of blast overpressures can be approximately scaled by the following formula:

where Z is a scaled distance, R is the actual effective distance from the explosion, and W is the weight of the explosion in TNT equivalent kilogram. The scaled distance is then used to estimate the overpressure by the following formulas:

If the pressure wave encounters a structure, it will be reflected off the front face creating a localized reflected overpressure. The pressure wave will continue until it encounters the back side of the building where it will generate a negative pressure wave of the appropriate magnitude on the structure.

Sufficient overpressure can destroy nonhardened buildings, but the real damage can be to the personnel in the blast area. Loss of life and limb and permanent hearing loss can result. According to the US Department of Defense’s Structures to Resist the Effects of Accidental Explosions, UFC 3-340-02 (December 2008), the range of damage to humans starts at about 5 psi for hearing loss, and the damage increases substantially to about 80 psi where the lungs collapse. Table 3.3 helps explain the damage.

Organ	Pressure (kPa)	Damage
Ears	6.2 at 0.207 kPa-m/s	Threshold shift in hearing (log scale)
	2.0 at 0.069 kPa-m/s
	34.5	Threshold eardrum rupture
	103.4	50% eardrum rupture
Lungs	206–276	Threshold for lung damage
	P > 552	50% lethality for lung damage
Whole body	670–830	Threshold for whole body
	900–1250	50% lethality
	1380–1750	<1% survival

^a From Blast injuries. Estimated human tolerances for single, sharp, rising blast waves. Courtesy of Bowen TE and Bellamy RF, editors. Emergency War Surgery. Washington, DC: United States Government Printing Office, 1988. http://emedicine.medscape.com/article/822587-overview.

Example of an explosive device:

A truck with an explosive device estimated a 1.5 metric tons is approaching a checkpoint. If we assume that the material is ANFO, how far out is the blast range for buildings and personnel?

First, calculate the power of the explosive in TNT equivalent.

ANFO is equivalent to about 0.8 TNT, so 1.5 MT of ANFO is equivalent to 1.2 MT of TNT.

Note that the TNT will have a density of about 1.5 kg/l so the volume will be just under a cubic meter—actually (0.8 m³).

For distances, the scaling distance Z will be the measured distance Z = R/(1200)^1/3 or for this explosive quantity Z = R/10.627.

Then, the pressures in kPa are in Table 3.4.

A plot of the data is shown in Figure 3.2.

R (m)	20	50	100	150	200	250	300
Z	1.89	4.72	9.43	14.14	18.86	23.58	28.3
Overpressure (kPa)	290	34.67	12.28	7.70	6.67	4.51	3.75

According to these calculations, anyone closer than about 30 m from the source will have about a 1% chance of survival, while severe injuries will occur at 20–30 m, and people at about 100 m will have a 50% chance of eardrum rupture. Glass breakage occurs at about 15–20 kPa. That suggests that a distance of 100 m should be sufficient to protect most of the command and control facilities of a modern industrial plant and dispatch center should be at least 100 m from a checkpoint unless the glass in the center is blast proof and reinforced.

This also suggests that any shipping and receiving inspection stations should be in a remote location, away from the warehouse and well away from the center of the plant.

Other Types of Incidents and Accidents

For an examination of the likelihood of other chemical accidents or incidents, it is recommended that one should use a chemical hazard incident evaluation program. There are several programs on the market and a free program from NASA/USCG, which is called ALOHA. Other programs are available from the Protective Design Center (US Department of Defense) that has proprietary software, the US Nuclear Regulatory Commission that has chemical specific hazard spreadsheets in the public domain, and a number of commercial software programs.

There are also a number of good references on the subject of blasts, explosives, and building hardening. These include:

• US Department of Energy. A manual for the prediction of blast and fragment loadings on structures. Amarillo (TX): U.S. Department of Energy; 1992. Report no. DOE/TIC 11268.
• Air Force Engineering and Services Center. Protective construction design manual. Tyndall Air Force Base (FL): Air Force Engineering and Services Center, Engineering and Services Laboratory; 1989. Report no. ESL, TR87-57.
• Committee on Feasibility of Applying Blast-Mitigating Technologies and Design Methodologies from Military Facilities to Civilian Buildings, Division on Engineering and Physical Sciences, Commission on Engineering and Technical Systems, National Research Council. National Academies Press, Oct 26, 1995, Political Science, p. 112.
• Ngo T, Mendis P, Gupta A, Ramsay J. Blast loading and blast effects on structures—an overview. Electric Journal of Structural Engineering Special Issue Loading on Structures 2007;75–91.