Explosion Containment: ARC Results, and the Noble-Abel Equation

The Accelerating Rate Calorimeter [ARC] provides rates of reaction [or decomposition], in terms of temperature and pressure increase rates, and quasi-adiabatic maximum temperatures and pressures. However, the amount of material in the 10-cubic-centimeter test cell is controlled by (1) the maximum allowable working pressure of the cell and (2) heat absorption by the cell wall. That is, a high "loading density" [grams per cubic centimeter] provides a closer approach to adiabatic behavior but risks rupture of the cell, and a low "loading density" requires significant correction of the test results to account for the cell-wall heat absorption. Use of the Noble-Abel equation allows extrapolation and interpolation of ARC pressure data, via a straight line on reciprocal/reciprocal graph paper, with only one test. Thus, a maximum loading density for an ARC cell can be estimated. Also, the ability of process equipment to contain the gaseous and vapor products of a reaction [or decomposition], or the need to provide overpressure protection can be determined. This applies particularly to process equipment containing "Z" [nitrogen-containing] compounds - as in some pharmaceutical materials - where decomposition changes "solid" nitrogen to nitrogen gas, as might occur during fire exposure. Further, the Noble-Abel calculation allows adjustment of the pressure rate in the A/V "Fauske" relationship for "hybrid" two-phase venting. Examples of the Noble-Abel equation are 1/d = (41,500/P) + 1.2, for black powder [experimental], for P in psia and d in g./cu.cm., and 1/d = (87,600/P) + 1.2 for dimethyl tetrazole [calculated].