A Reactivity Example Problem

A train has collided with a truck at an intersection in the industrial section of a major city. A tank car and a flatbed car filled with containers have derailed. Now the tank car is lying in a ditch alongside the tracks, surrounded by some containers that have broken loose from the flatbed car.

• The tank car is labeled "hydrogen fluoride."
  
• The UN/NA number shown on all the containers is 1806. (The UN/NA number is the United Nations-North America number. This numbering system was developed by the U.S. Department of Transportation, and has since become the UN standard system for classifying hazardous materials.)

If you were responding to this incident, you would want to know:

What problems could occur if these chemicals were to be mixed together when crews right the tank car and collect the containers?

You can use the Chemical Reactivity Worksheet (CRW) to answer this question, as described below.

Working the Problem

First, download and install the CRW, if you haven't already done so, then start it.

Click OK at the bottom of the opening screen to view the Mixture Worksheet. You'll "mix" the two chemicals by finding them in the database and adding them to the Mixture Worksheet. The CRW will then predict the mixture's potential reactivity.

Next, you'll need to search the database for each of the two chemicals you want to add:

1. Perform a basic search for chemicals with names that include "hydrogen fluoride." To do this, click New Search in the upper left corner, then type "hydrogen fluoride" in the Chemical Name text box:
   
   
   
   Then click Search.

2. "Hydrogen fluoride, anhydrous" is the fifth of the nine chemicals found. Double-click the chemical name to open the Chemical Datasheet. Check the information about the characteristics of hydrogen fluoride:
   
   • Check the Special Hazards box to see that hydrogen fluoride is both water- and air-reactive.
     
   • Check General Description to learn its general physical characteristics.
     
   • On the Reactivity tab, the topics Air and Water Reactions, Chemical Profile, and Reactive Groups tell you more about its reactions with air and/or water and other materials, and which reactive groups include hydrogen fluoride.

3. Click Add Chemical to Worksheet to add hydrogen fluoride to the Mixture Worksheet. In the message that appears, click Yes to view the Mixture Worksheet.

   
   

4. Perform another search for chemicals with the UN/NA number of 1806. To do this, click New Search. Set up your search so it looks like the picture below, then click Search. (Numerous other criteria are available if you click Show More Search Fields on the Basic Chemical Search window.)
   
   

5. This time, you'll find just one chemical: phosphorus pentachloride. Double-click the chemical name to check its characteristics. Click Add Chemical To Mixture to add it to the Mixture Worksheet, then click Yes to view the worksheet now.

6. Check the Mixture Worksheet to see statements about the mixture's potential reactivity. Click Predict Hazards in the lower right section, then scroll to view the predicted hazards for hydrogen fluoride mixed with phosphorus pentachloride. (The predicted hazards are based on the reactive groups of the items in the mixture.)
   
   

   These statements tell you that the response team would need to be prepared for a possible explosion and release of a toxic gas, if the two chemicals were to accidentally mix.

7. Another area where you should gather information is the Compatibility Chart. In the lower right of the Mixture Worksheet, click the button, Show Compatibility Chart. In the table, click one of the cells that represents the combination of hydrogen fluoride and phosphorus pentachloride. Then, review the information provided under each of the tabs: Hazard Summary, Potential Gases, Potential Gas Documentation, and General Documentation.

As you plan your response to this accident, double-check the information specific to each chemical to learn more about potential hazards. To review all information about each chemical, in the Mixture Worksheet, double-click on the name of either chemical, then review the information provided in the Chemical Datasheet. (Once you've reviewed the information, click Worksheet in the upper left corner to return to the Mixture Worksheet.)

To learn more about how to interpret the results you obtain from the CRW, check our list of Tips for CRW Users (see link in navigation bar).

Final Note: In this exercise, you "mixed" two chemicals together to learn about their potential reactivity hazard. You can add more than two chemicals to a mixture. But whenever you do so, be aware that the CRW only predicts the potential reactivity between two chemicals at a time (to predict the reactivity of a mixture of more than two chemicals, it predicts the reactivity of all possible pairs). This means that the CRW can't recognize situations when more than two chemicals react together.

For more information

Chemical Reactivity Worksheet Specialist Contact the CRW Specialist with questions or comments.