Last updated March 8, 2016

Frequently Asked Questions (FAQs) about the Chemical Reactivity Worksheet

Here are answers to questions about the Chemical Reactivity Worksheet (CRW), grouped into categories:

CRW Basics

Q. What is the latest version of the CRW? Where can I get it?

A. The latest version is 4.0.0 and it was released on March 3rd, 2016. You can download this version from the CRW download page.

Q. What changes have been made to the CRW over the years?

A. In the CRW Development History section, you can learn about the changes made to each version of the worksheet.

Q. Who created the CRW?

A. The CRW was initially developed by NOAA's Office of Response and Restoration and the Environmental Protection Agency in collaboration with the Center for Chemical Process Safety. Version 3.0 featured the additional collaboration of scientists from the Dow Chemical Company, and version 4.0 was developed in collaboration with experts from Dow, Dupont, Phillips, and The Materials Technology Institute.

Q. What are the main components of the CRW?




Mixture Manager

Create and manage chemical mixtures, and find chemicals to add to your mixtures.

Mixture Report

Preview or print a text report on the predicted hazards from mixing chemicals in any of your mixtures.

Compatibility Chart

View reactivity predictions for your mixtures as charts that you can annotate, print, or export.

Reactive Group Information

Assign new "custom chemicals" to reactive groups (categories of chemicals that react in similar ways), or add a reactive group to a mixture to represent a chemical that isn't in the CRW chemical library.

Custom Chemicals

Add your own custom chemicals to the CRW chemical library, or view, edit, or delete custom chemicals you've already added.

Absorbent Incompatibilities

Research known incompatibilities between common classes of absorbents and chemicals in the CRW database.

Materials of Construction

Research known incompatibilities between materials of construction, elastomers, and chemicals commonly used in the chemical industry.

File and Edit menus

Back up or restore your data, export or print compatibility charts and reactivity reports.

Q. Where can I find more information about the CRW?

A. The development team of the CRW version 3 has written a paper, Enhanced NOAA chemical reactivity worksheet for determining chemical compatibility, published in Process Safety Progress, that addresses previously identified limitations with CRW version 2.0, describes several enhancements have been incorporated into CRW 3.0 to help users generate and present chemical compatibility charts, and covers the development and use of this new tool. You can also contact us with specific questions.

Chemical Reactivity

Q: What is chemical reactivity?

A. Chemical reactivity is defined as the tendency of substances to undergo chemical change. While some chemical changes are harmless, others can lead to hazardous conditions. For example, two chemicals might react together to produce a toxic gas or cause an explosion. You can use the CRW to add chemicals to a virtual mixture, and then predict the potential hazards if chemicals in that collection were to mix together. You can also access datasheets on individual chemicals to view information such as reactivity profiles and special hazard alerts.

Q. What are reactive groups?

A. Reactive groups are categories of chemicals (such as "acyl halides" or "ketones") that react in similar ways because they are similar in their chemical structure. For the purposes of predicting potential reactivity between chemicals, each chemical in the CRW has been assigned to one or more reactive groups, based on the known chemistry of that chemical. (To see descriptions of all the reactive groups used in the CRW, click the Reactive Groups button in the taskbar at the top of the CRW interface.)

Q: How does the CRW predict reactivity between chemicals?

A. To predict the potential reactivity of a mixture of chemicals, the CRW first identifies the reactive groups to which the chemicals belong, and then predicts the kind of pair-wise reactions likely to occur when members of these groups are mixed together.

Q: What are pair-wise reactivity predictions?

A. The CRW only accounts for reactions between two chemicals at a time. If your mixture contains more than two chemicals, the CRW predicts the reactivity between all possible pairs of those chemicals.

Important Note: When there are three or more substances in a mixture, they may react together in ways that the CRW's pairwise reactions can't predict:

  • For example, glycerin and nitric acid react very little when they're mixed together. However, if sulfuric acid is added to the mix, the three chemicals react together to produce the powerful explosive nitroglycerin. The CRW doesn't predict this reaction, because it looks at the pairs (glycerin + nitric acid; glycerin + sulfuric acid; and nitric acid + sulfuric acid) rather than all three chemicals together.
  • In other cases, one of the chemicals may act as a catalyst that accelerates the rate of reaction between other chemicals in the mixture. For example, nickel carbonyl catalyzes many polymerization reactions and other kinds of synthetic organic reactions. In such cases, the reactivity hazard may be greater than predicted.

However, reactions among more than two chemicals are relatively uncommon in nature, except for the catalyzed reactions that are common components of the metabolic processes of living organisms.

Working With Mixtures

Q. Can I add as many chemicals as I want to a mixture?

A. The current limit is 100 chemicals.

Q. Is there a way I can add additional chemicals to the CRW database?

A. Yes. Beginning with version 2.0, you can add your own chemicals to the CRW database. Once they're part of the database, you can create mixtures of those chemicals with other chemicals in the database, to see how they might react. Click on the Custom Chemicals button in the CRW taskbar to create and manage your custom chemical list.

Q. Is there a way to see how chemicals in the mixture react with water?

A. Yes. There are several ways to add water to any mixture. Here's the easiest way:

On the Mixture Manager screen, click the "Add:" drop-down menu in the lower right corner and select Water to include water in the mixture.

Adding water to a mixture allows you to see general predictions about how the chemicals would react with water. However, if a chemical is water-reactive, check its chemical datasheet, where you may find more specific information about its water reactivity.

Q: Can I add a reactive group to the mixture?

A. You can add reactive groups—as well as specific chemicals—to a mixture. You may want to do this if, for example, you know that a substance is a strong base, but you don't know its name or CAS registry number. Click on the Reactive Groups button in the taskbar at the top of the CRW screen, select the name of the reactive group that you want to add, and then click Add Selected Group to Mixture.

Reactivity Predictions

Q. I used the CRW to "mix" some chemicals together, and it predicted "No known hazardous reaction." Should I trust this prediction?

A. We believe that the CRW accurately predicts whether or not a reaction will occur between two chemicals that you select. But sometimes, there's more to the story. For instance, to predict the reactivity of a mixture of more than two chemicals, the CRW predicts the reactivity between all possible pairs of those chemicals. But sometimes, three or more chemicals can react together in ways the CRW can't predict. In some cases, for example, a chemical may catalyze (speed up) the reaction between two other chemicals, making that reaction more violent than the CRW would predict.

In multiple places in the CRW, the program alerts you to hazards. You should review all of them when assessing reactivity:

  • Chemical Datasheet: Once you've added chemicals to the mixture on the Mixture Manager screen, click on the green Info button to the left of a chemical's name to display its chemical datasheet. The datasheet provides a general description of the chemical, a list of special hazards, a reactivity profile, reactive group assignments, and details about whether the chemical reacts with air or water.
  • Mixture Report: Once your mixture collection is complete, click Mixture Report in the taskbar to display the potential hazards of your mixture. After you have reviewed the predicted hazards, click the Mixture Documentation tab to view citations of published research related to this combination of chemicals. Keep in mind that these research results (or the described events) may not match the results of your mixture, possibly because the chemicals or the scenario conditions are slightly different.
  • Compatibility Chart: After you've reviewed the predictions in the Mixture Report, click Compatibility Chart in the taskbar or View Chart on the Mixture Manager screen to display the compatibility chart for the mixture. You can click in individual chart cells to see the reactivity details for that pair of chemicals. When you select a cell, specific hazard predictions and potential gas products are listed on the bottom of the page, along with documentation supporting those predictions.

Q. When I combined nitric acid and sodium hydrosulfide solution, one of the hazard statements was "Reaction liberates gaseous products and may cause pressurization." Can the CRW tell me what gases could be expected?

A. Yes. In the Compatibility Chart, click the cell for that pair of chemicals. On the Potential Gases tab at the bottom of the page, the CRW predicts that sodium hydrosulfide solution mixed with nitric acid produces hydrogen sulfide, nitrogen oxides, and acid and base fumes.

Technical Details

Q. What computer operating systems are compatible with the CRW?

A. You can install and run the CRW on the following systems:

PCs running Windows (32 and 64 bit operating systems):

·         Windows 10 Pro Edition
Windows 10 Enterprise Edition

·         Windows 8.1 Standard Edition
Windows 8.1 Pro Edition

·         Windows 8 Standard Edition
Windows 8 Pro Edition

·         Windows 7 SP1 Ultimate, Professional, Home Premium

Mac operating systems:

·         OS X El Capitan v10.11

·         OS X Yosemite v10.10

·         OS X Mavericks v10.9

Tablet and mobile device operating systems:

  • Not currently supported

Q. Do we need to obtain either individual or site licenses to use the CRW?

A. No. You do not need a license and you do not need to register. The CRW is a free, standalone program. No additional software is required for its operation. There is no end user registration requirement. CRW users are encouraged to periodically check this website for updates and announcements regarding the CRW4 tool.

Q. Can we run the CRW from a server?

A. The CRW4 is primarily designed to run as a standalone program. However, the environment in which the CRW4 was developed provides for client-server and peer-to-peer configurations that require knowledgeable technical support. For an initial overview of these options, please refer to the Data Sharing video, which can be found on this website or by clicking the orange Data Sharing button in the CRW taskbar. If you have further questions or would like more information, please contact us.

Q. What kind of software is the CRW?

A. Beginning with version 2.0, the CRW has been created with FileMaker Pro, a fully relational database program that allows us to bundle the chemical data with the FileMaker Runtime engine.