6/9/2015Eric Grulke. fires & explosions. CME The Wily Coyote Lecture Fires and Explosions CME 470

6/9/2015Eric Grulke. fires & explosions. CME Caution!

6/9/2015Eric Grulke. fires & explosions. CME Fire vs. Explosion Fires: release energy slowly Explosions: rapid release of energy

6/9/2015Eric Grulke. fires & explosions. CME Fire or Explosion?

6/9/2015Eric Grulke. fires & explosions. CME Fire Triangle Fuels Solids: plastic, wood dust fiber, metal particles Liquids: gasoline, acetone, ether, pentane Vapors: acetylene, propane, CO, H 2 Oxidizers Solids: metal peroxides, ammonium nitrate Liquids: H 2 O 2, nitric acid, perchloric acid Vapors: O 2, F 2, Cl 2 Ignition sources Sparks Flames Static electricity heat

6/9/2015Eric Grulke. fires & explosions. CME The Fire Triangle

6/9/2015Eric Grulke. fires & explosions. CME Definitions Combustion: chemical reaction in which fuel combines with oxidant and releases energy Ignition: start of the burning process Autoignition temperature: T such that mixture can self-ignite Flash Point: lowest temperature at which the liquid will volatilize enough vapor to form an ignitable mixture

6/9/2015Eric Grulke. fires & explosions. CME Definitions Fire point: lowest T at which vapor above a liquid will burn Flammability limits: burning occurs between LFL and UFL (LEL and UEL) Explosion: rapid expansion of gases with fast pressure or shock wave Mechanical Explosion: explosion due to vessel failure, high pressure non-reactive gas

6/9/2015Eric Grulke. fires & explosions. CME Definitions Deflagration: explosion with shock wave moving at a speed lower than speed of sound Detonation: explosion with shock wave moving faster than speed of sound Confined explosion: explosion inside vessel or building Unconfined explosion: flammable gas spill

6/9/2015Eric Grulke. fires & explosions. CME Definitions Boiling liquid expanding vapor explosion (BLEVE): vessel containing liquid at T>T b ; explosive vaporization of vessel contents Dust explosion: rapid combustion of fine particles Shock wave: pressure wave moving through a gas Overpressure: P as f(shock wave)

6/9/2015Eric Grulke. fires & explosions. CME Flammability Characteristics of Liquids and Gases Liquids – use flash point temperature to characterize the fire and explosion hazards FPT – determined in open-cup apparatus; open flame over liquid which is heated; closed-cup apparatus gives lower T

6/9/2015Eric Grulke. fires & explosions. CME Flammability Characteristics of Liquids and Gases

6/9/2015Eric Grulke. fires & explosions. CME Flammability Characteristics of Liquids and Gases

6/9/2015Eric Grulke. fires & explosions. CME Flash Point FP’s are tabulated Multicomponent mixtures: one component is flammability and its characteristics are known Estimate is based on the partial pressure of the flammable component K. Satyanarayana, P. G. Rao, Improved equation to estimate flash points of organic compounds, J. Hazardous Materials, 32, (1992). Coefficients tabulated for chemical groups.

6/9/2015Eric Grulke. fires & explosions. CME Example 6-1. Flash point of MeOH solution

6/9/2015Eric Grulke. fires & explosions. CME Saturation Vapor Pressure for Methanol

6/9/2015Eric Grulke. fires & explosions. CME Concentration of Flammable Gas (vol%)

6/9/2015Eric Grulke. fires & explosions. CME Vapor Flammability LFLs and UFLs can be computed for mixtures using an equation by Le Chatelier

6/9/2015Eric Grulke. fires & explosions. CME LFL = f(T, P)

6/9/2015Eric Grulke. fires & explosions. CME Estimating LFL, UFL C st is the volume % fuel in fuel plus air

6/9/2015Eric Grulke. fires & explosions. CME Minimum Oxygen Concentration LFL is based on fuel in air A minimum oxygen level is needed to propagate a flame Below the MOC, the flame cannot generate enough energy to heat the mixture for self-propagation MOC is estimated using the stoichoimetry of the combustion and the LFL

6/9/2015Eric Grulke. fires & explosions. CME Minimum Ignition Energies

6/9/2015Eric Grulke. fires & explosions. CME Ignition Sources of Major Fires

6/9/2015Eric Grulke. fires & explosions. CME Reaction and Pressure Fronts Propagating Through a Pipe

6/9/2015Eric Grulke. fires & explosions. CME Test Apparatus for Acquiring Vapor Explosion Data

6/9/2015Eric Grulke. fires & explosions. CME Typical Pressure Versus Time Data Obtained from Explosivity Apparatus

6/9/2015Eric Grulke. fires & explosions. CME Pressure Rate and Maximum Explosion Pressure as a Function of Vapor Concentration

6/9/2015Eric Grulke. fires & explosions. CME Typical Explosion Data Exhibiting the Cubic Law

6/9/2015Eric Grulke. fires & explosions. CME Average K g Values for Selected Gases

6/9/2015Eric Grulke. fires & explosions. CME Average K St Values for Selected Dusts

6/9/2015Eric Grulke. fires & explosions. CME Effect of Initial Pressure on Maximum Explosion Pressure and Rate

6/9/2015Eric Grulke. fires & explosions. CME Explosion Data for Propane Showing Peaks Indicative of the Onset of Detonation

6/9/2015Eric Grulke. fires & explosions. CME Damage Produced by Overpressure

6/9/2015Eric Grulke. fires & explosions. CME Correlation Between Overpressure and Scaled Distance, English Engineering Units

6/9/2015Eric Grulke. fires & explosions. CME Correlation Between Overpressure and Scaled Distance, SI Units

6/9/2015Eric Grulke. fires & explosions. CME Maximum Horizontal Range of Blast Fragments

CASE STUDY: TNT Images from Wikipedia.org 6/9/2015Eric Grulke. fires & explosions. CME

TRINITROTOLUENE 2,4,6-trinitrotoluene CAS Reg # Formula: C7H5N3O6 Fw = kg/kmol Names: TNT, Trotyl, Triton, … Density: 1654 kg/m 3 Melting point: C; boiling point: 295 C (decomposition) Solubility: 0.13g/L in water; soluble in ether, acetone, benzene, pyridine EU classification: explosive (E), toxic (T), environmental hazard (N) NFPA 704 6/9/2015Eric Grulke. fires & explosions. CME

background Common explosive with convenient handling properties C 6 H 2 (NO 2 ) 3 CH 3 Standard measure of explosive strength Synthesis: multi-step process. Nitration of toluene (nitric + sulfuric acid) to MNT/separation/nitration to DNT then nitration to TNT in anhydrous mixtures of nitric acid + oleum. NO X in feed nitric acid must be controlled to prevent oxidation of methyl group. Stabilization: aqeous sodium sulfite to remove less stable isomers and other byproducts. Rinse water is a significant pollutant. 6/9/2015Eric Grulke. fires & explosions. CME

applications Common explosive for military and industrial applications Low sensitivity to shock & friction; ignition temperature is well above the melting point Does not sorb water, relatively stable. Block sizes: 0.25, 0.5 and 1 kg. Synergistic blends with other exposives 6/9/2015Eric Grulke. fires & explosions. CME

Explosive characteristics 6/9/2015Eric Grulke. fires & explosions. CME Explosives decompose to elements, stable molecules (mostly) without the aid of external oxidizing agents. Exothermic, high activation energy Carbon is a product, leading to sooty appearance of explosions Ignition with a high velociy initiator or by concussion Reference point – Figure of Insensitivity The Figure of Insensitiveness is determined from impact testing, typically using a drop-weight tower. In this test, a small sample of the explosive is placed on a small steel anvil which is slotted into a recess in the base of the drop tower. A cylindrical, 1 kilogram steel weight (mounted inside a tube to accurately guide its descent to the impact point in the centre of the anvil) is then dropped onto the test specimen from a measured height. The specimen is monitored both during and after this process to determine whether initiation occurs. This test is repeated many times, varying the drop height according to a prescribed method. Various heights are used, starting with a small distance (e.g. 10 cm) and then progressively increasing it to as high as 3 metres. The series of drop heights and whether initiation occurred are analysed statistically to determine the drop height which has a 50% likelihood of initiating the explosives. The intention of these tests is to develop safety policies/rules which will govern the design, manufacturing, handling and storage of the explosive and any munitions containing it.

Energy content 4.6 megajoules/kg (energy density) –Nuclear weapons are measured in megatons of TNT –Gunpowder: 3 MJ/kg –Dynamite: 7.5 MJ/kg –Gasoline: 47.2 MJ/kg (gas+O 2 =10.4 MJ/kg) 6/9/2015Eric Grulke. fires & explosions. CME

6/9/2015Eric Grulke. fires & explosions. CME ton TNT explosion, 1965, wikipedia.org Note white blast wave at water surface and condensate cloud caused by shock wave.