Consequence modelling software for accidental releases of flammable or toxic chemicals to the atmosphere includes discharge modelling, atmospheric dispersion modelling and evaluation of flammable and toxic effects. Scenarios which may be modelled includes releases from vessels (leaks or catastrophic ruptures), short pipes or long pipes. Releases considered include releases of sub-cooled or superheated liquid (with or without rainout), or vapour; un-pressurised or pressurised releases; and continuous, time-varying or instantaneous releases. For flammables, ignition may lead to rising fireballs, jet fires, pool fires and vapour cloud fires or explosions. Testing of the software should ideally include for each consequence model "verification" that the code correctly solves the mathematical model (i.e. that the calculated variables are a correct solution of the equations), and "validation" against experimental data to show how closely the mathematical model agrees with the experimental results. The current paper includes an overview on how the above verification and validation is carried out for the latest consequence models in the hazard assessment package Phast and the risk analysis package Safeti. Reference is made to the literature for the availability of experimental data. Thus, an extensive experimental database has been developed including experimental data for validation for the above models and scenarios, where many different chemicals are considered (including water, LNG, propane, butane, ethylene, ammonia, CO2, hydrogen, chlorine, HF etc.).