As the name implies, the ARSST is well suited for basic process safety screening tests, particularly if one has only limited knowledge of the material being tested. ARSST technology was originally developed as a short-cut alternative to VSP2 testing. ARSST tests are easy to perform and require little specialized training. The tests generally are much quicker to set up than VSP2 tests, and the cost of consumables is low. The sample size is relatively small (several grams), which is an advantage during early process development when material can be scarce, or when very energetic materials are encountered, or when decomposition products are particularly hazardous and call for special cleanup procedures like gas scrubbing and acid neutralization. Typically, an ARSST test uses about a 10 ml sample, although samples as small as 1 g have been successfully tested.
ARSST tests are normally performed in what is called “open cell” mode. In open cell testing, vaporization (boiling) is suppressed by imposing an initial nitrogen gas “pad” in the containment vessel. For example, an inert gas pad pressure of 300 psi (20 bar) is typically enough to substantially increase the boiling point of the liquid reactants, such that there is negligible loss of reactants during the test. In fact, through numerous DIERS round robin exercises we have demonstrated excellent agreement between open cell ARSST data and closed cell VSP2 data, in particular with regard to data for vent sizing.
If non-condensable gas is generated in an ARSST test, then it accumulates in the surrounding containment vessel (350 or 450 ml) and the molar rate of gas generation is readily estimated using the measured pressure rise rate and the ideal gas law. Note that open cell testing is the recommended approach for gassy systems, which would be difficult to accommodate in a light weight closed cell due to extremely high pressures, gas volume uncertainty, and solution effects. Although VSP2 tests can also be done in open cell mode, the ARSST is often preferred for gassy decompositions simply because there is less material to handle and clean up. A closed cell ARSST option is also available and is useful for certain screening applications but it is not suitable for vent sizing data.
The ARSST can be used to demonstrate whether tempering (boiling) at the relief set pressure is sufficient to suppress a runaway reaction. This is done by running the open test at the relief set pressure, say Pset = 15 psi (1 bar), by using a 15 psi (1 bar) pad rather than 300 psi (20 bar). One such example is an organic peroxide/solvent solution where a sustained fire heats the mixture and then boils off the solvent, during which time there may be some decomposition of the peroxide. If there is insufficient solvent latent heat available, then following solvent boil off the subsequent decomposition rate of the remaining peroxide heel is inferred directly from the measured pressure rise rate. The ARSST is well suited for direct fire simulation testing (up to 30ºC/min)
Liquid can be added directly to the ARSST test cell during a test using a fill tube. Samples are agitated using a magnetic stirrer. Test cells are normally made of lightweight glass to achieve a low phi-factor. It is also possible to use a heavier metal cell such as an ARC bomb, although this is not common because the associated high phi-factor means the data are not directly scalable.
ARSST data are used to model such upset scenarios as loss of cooling, loss of stirring, mischarge of reagents, mass-loaded upset, batch contamination and fire exposure heating. This easy-to-use and cost-effective calorimeter can quickly and safely identify potential reactive chemical hazards. ARSST data yield critical rates of temperature and pressure rise during a runaway reaction, thereby providing reliable energy and gas release rates which can be applied directly to full scale process conditions.
ARSST Benefits
The ARSST represents Minimum Best Practice and is based on established DIERS technology which is recognized by OSHA as an example of good engineering practice. This easy-to-use device is capable of quickly generating low phi-factor data for DIERS vent sizing and is an excellent tool for industry as well as any university chemistry or chemical engineering lab for research or unit operation studies. The ARSST enables users to quickly obtain reliable adiabatic data which can be used for a variety of safety applications including vent sizing, characterization of material compatibility, thermal stability and reaction chemistry. Test data include adiabatic rates of temperature and pressure change which, due to the low thermal inertia, can be directly applied to process scale.
