All packaged organic peroxides have a characteristic temperature at which self-heating accelerates. This temperature is known as the Self-Accelerating Decomposition Temperature (SADT) and it occurs when the rate of peroxide decomposition is sufficient to generate heat at a faster rate than it can dissipate into the environment.
Although temperature is the main factor in determining the decomposition rate, the size of the packaging is also important because it has an effect on the dissipation of the heat. As a general rule, larger packaging will contribute to a lower SADT and for this reason the packaging is also taken into account when the SADT calculations are made.
The SADT for an organic peroxide formulation is usually lower the more concentrated the formulation. Dilution with a compatible high boiling point diluent will usually increase the SADT since the peroxide is dilute and the diluent can absorb some if not most of the heat, minimizing the increase in temperature.
Most organic peroxides react to some degree or another with their decomposition products during thermal decomposition, and this often increases the rate because the decomposition proceeds more rapidly as the decomposition products are generated.
The SADT measurement is calculated as follows:
- The package containing the peroxide is placed in an oven set at the test temperature.
- The timer starts when the product reaches 2°C below the intended test temperature.
- The oven is held at a constant temperature for up to one week or, until a runaway event occurs.
- The test is classed as a “pass” if the product doesn’t exceed the test (oven) temperature by 6°C within one week.
- The test is classed as a “fail” if the product exceeds the test temperature by 6°C within one week.
- The test is repeated in 5°C increments until a failure occurs.
- The fail temperature is reported as the SADT for that package and formulation.
- Secondary information about the violence of the decomposition can also be recorded.
Strict temperature control and high temperature alarms systems are required when storing organic peroxides and many peroxides require refrigeration, which will also require an alarm system to warn of a failure or a temperature that has gone outside the specified temperature range.
Contamination may also accelerate the decomposition of organic peroxides, for example most heavy metal compounds have an accelerating effect on decomposition, and acids, bases and accelerators may cause decompositions to occur at temperatures significantly lower than the recommended storage temperature. This is why you must store your organic peroxides separately from all other chemical compounds, unless complete compatibility has been proven.
Most organic peroxides should be considered highly combustible and once they have ignited many will burn vigorously. If they heat up to their decomposition temperature, organic peroxides will generate vapours, which may be flammable, therefore you should ensure there are no potential ignition sources in or around the storage area and all electrical equipment will need to be explosion-proof . It is of course possible for auto ignition to take place, and with that in mind the appropriate fire-fighting equipment should be available both in and remote from the storage area.
Because organic peroxides produce vapours during decomposition, pressure build-up occurs in the package. To prevent excess pressure build-up within the storage area due to prolonged decomposition and damage occurring to the packaging, the storage area must be fitted with a pressure relief mechanism.
Find out more about organic peroxides and their safe handling and storage in our Resources section.