2 Ways To Screen Chemicals for Reactivity Hazards

This guest post is written by Dr. Sanjeev Saraf, Senior Associate in Exponent’s Engineering Management Consulting practice. Dr. Saraf’s primary focus is on evaluating processes/products for increased safety, reliability, and economic feasibility. You can read more from the author on his process safety and risk management blog.

The reactivity hazard of a substance is normally assessed by performing thermal analysis. A small amount of the sample is heated over a range of temperature (usually within 30°C – 400°C), and temperature, pressure, and time data are recorded. This information is then used for alarm settings, relief  sizing, and process modeling.

Assessing reactivity is calorimetric analysis, which can be resource consuming and thus possible only for a limited set of compounds.

Often, you are required to answer the question – Is there potential reactive chemistry? – knowing only the molecular structure.

To answer this question, you can use a variety of tools:

  • functional groups indicative of reactivity hazards
  • using group contribution method to estimate energy of reaction
  • develop incompatibility matrix
  • reactivity data available through MSDS or Bretherick’s Handbook
  • Oxygen balance
  • Calculated Adiabatic Reaction Temperature (CART)
  • ASTM CHETAH program

I will discuss couple of popular techniques used to determine potential reactive chemistry.

Functional Groups
The presence of certain functional groups is considered an indicator of reactivity. This is the simplest reactivity screening method possible and serves as a guideline for further analysis. For example, chemicals containing the following functional groups can be considered potentially reactive:

  • -NO2 : organic nitro compounds
  • -O-O-, -O-OH : organic/inorganic peroxide and hydroperoxide compounds
  • -C   C- : triple bonded carbon atoms as in acetylene and acetylenic compounds

I have summarized a few of the reactive groups in this table.

Chemical Incompatibility Worksheet
NOAA provides a free program, Chemical Reactivity Worksheet (CRW), that you can use to determine reactivity of a chemical or mixture.

NOAA Chemical Reactivity Worksheet includes:

  • a database of reactivity information for more than 5,000 common hazardous chemicals
  • rule-based algorithm allowing you to virtually “mix” chemicals to determine compatibility of two or more chemicals

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