The highly accelerated stress test (HAST) method was first proposed by Jeffrey E. Gunn, Sushil K. Malik, and Purabi M. Mazumdar of IBM.
The acceleration factor for elevated humidity is empirically derived to be
where RH<sub>s</sub> is the stressed humidity, RH<sub>o</sub> is the operating-environment humidity, and n is an empirically derived constant (usually 1âÂÂ<âÂÂnâÂÂ<âÂÂ5).
The acceleration factor for elevated temperature is derived to be
where E<sub>a</sub> is the activation energy for the temperature-induced failure (most often 0.7 eV for electronics), k is the Boltzmann constant, T<sub>o</sub> is the operating temperature in kelvins, and T<sub>s</sub> is the stressed temperature.
Therefore the total acceleration factor for unbiased HAST testing is