PHS.js is a JavaScript implementation of the Predicted Heat Strain (PHS) model described in the standard "ISO/FDIS 7933 Ergonomics of the thermal environment — Analytical determination and interpretation of heat stress using calculation of the predicted heat strain". PHS.js is based on "Predicted Heat Strain (PHS) model: computation program written in Quick Basic" in Annex E of the standard.

PHS.js export the following functions:

• par_spec_aoh – References to parameter specifications.
• reset – Set all variale values to NaN.
• sim_init – Initialize a simulation.
• state – Returns a number of variables which reflects the main state of the simulation.
• time_step – Do a time step in a simulation, returns the same as the function state.
• current_result – Returns variables showing the current main result of a simulation.
• sample_get – Returns a number of variable which can be used in the debugging of the simulation.

Loading PHS.js results in a global variable boj.PHS which contains an associative array with references to the exported functions.

Parmeters are handeled using parameter_util.js, which provide functions for setting default values and accessing the parmeters. In the beginning of PHS.js there are descriptions of the parameters. Parameters in par_spec_sim must not be changed during a simulation. Paramters in par_spec_step can be changed between time steps in the simulation.

The text below assumes the statetment var phs = boj.PHS;.

The main steps in a PHS simulation are:

1. (optional) phs.reset();
2. Set parameters using parameter_util.js.
3. phs.sim_init();
4. For each time step
   • phs.time_step();
   • (optional) save the return values.
   • (optional) change parameters.
5. phs.current_result()

PHS_wci.js (used by PHS.html) is an example of how PHS.js can be used.

One of the goal with PHS.js is to be CPU efficient. The time_step() function will be the most frequently used function and it should do as little as possible. Calculations which results do not changed in a time step are done by the change of parameters.