Chemical Reactivity Hazards Screening

Characterizing chemicai reactivity hazards invoives a review of the inherent thermai hazards of the pure process materiais as weii as the thermai hazards of the materiais under processing conditions. Gaining this understanding and characterizing thermaiiy hazardous systems is a muitistep process. 

---

Use reactor calorimetry testing to determine thermodynamics and kinetics of process. See Appendix 2A (Chemical reactivity hazards screening). 

Up to this point, the chemical reactivity hazards of individual substances, either by themselves or in contact with common environmental materials, have been considered. This last question in the chemical reactivity hazards screening will address the potential for an unintended chemical reaction due to incompatible materials contacting each other. Compatibility, in this context, means the ability of materials to exist in contact without specified (usually hazardous) consequences under a defined scenario. A scenario, in this context, is a detailed physical description of the process whereby a potential inadvertent combination of materials may occur (ASTM E 2012-00). 

Based on the level of knowledge of chemical reactivity hazards, determine if additional screening of reactivity hazards is necessary. Having reactive functional groups might indicate the need to perform literature searches, access databases, or run differential scanning calorimetry. 

FIG. 23 18 CCPS preliminary screening for chemical reactivity hazards. [From Johnson et al. (2003) copyright AIChE reproduced with permission. ]... 

Chapter 3 provides a screening tool to help determine whether chemical reactivity hazards are present that need to be managed and controlled. 

Chapter 3 is a Preliminary Screening Method designed to help identify whether chemical reactivity hazards are present at a facility. It can be used to determine whether the information in this publication is sufficient, or whether additional resources are going to be required, for managing identified chemical reactivity hazards. 

Table 3.1, Example Form to Document Screening of Chemical Reactivity Hazards, with the accompanying flowchart of Figure 3.1, for use with the preliminary screening method of Chapter 3. 

Table 2.3 gives one way for an existing facility to get started toward successfully managing chemical reactivity hazards. This assumes you already have an idea as to what chemical reactivity hazards must be addressed by the management system, such as by answering the questions in the Preliminary Screening Method of Chapter 3. 

Preliminary Screening Method for Chemical Reactivity Hazards... 

A form such as Table 3.1 can be used to document answers to the screening questions and the conclusions that are drawn. The flowchart in Figure 3.1 is an overview of how these questions are connected to determine whether a chemical reactivity hazard can be expected at your facility. 

This screening method may be used by either a single person or a group of persons. A team approach, involving several persons with different knowledge and functional perspectives, has the possibility of better identifying and assessing the potential for chemical reactivity hazards. 

Figure 3.1. Preliminary screening for chemical reactivity hazards summary flowchart.

If you are certain that NO incompatible materials have a reasonable likelihood of contacting each other and causing undesired consequences, then stop here. If the decision flow of Figure 3.1 has been followed, the Preliminary Screening Method indicates that no significant chemical reactivity hazards are expected at your facility. 

This chapter assumes chemical reactivity hazards exist at your facility. If you are uncertain whether or not you have any chemical reactivity hazards, the Preliminary Screening Method in Chapter 3 can be used to help identify whether chemical reactivity hazards may be present. 

The list in Table 4.2 indicates the basic chemical reactivity hazard information that needs to be known for each substance. This is an extension of the information needed for the Preliminary Screening Method of Chapter 3. The Glossary at the end of of this publication gives definitions for most of the terms used in the table. 

Use of the Preliminary Screening Method of Chapter 3, along with the chemical reactivity data collected so far (Section 4.2), should begin to give at least a qualitative idea of the chemical reactivity hazards that may be present in an actual or proposed facility. However, the absence of particular information does not imply that no hazards exist. For this reason, a systematic search to attempt to identify all chemical reactivity hazards, in the context of how materials will be used in the actual process, is the next step in effectively managing chemical reactivity hazards. If a particular hazard is not recognized, it is not likely to be adequately controlled. 

Several worked examples of identifying chemical reactivity hazards are presented in this chapter. The objective of this chapter is to illustrate the use of the Preliminary Screening Method for Chemical Reactivity Hazards (Chapter 3) by way of a few, relatively simple examples that show different decision paths. 

Table 5.1 shows what the documentation of the screening might look like for this example, if the user decided to proceed to answer the remaining questions. The Comments column is used to indicate where information was obtained for answering each question. The information in Table 5.1 gives an idea of what chemical reactivity hazards will need to be controlled to operate the facility safely. 

In a Downstream Decomposing facility not the subject of this example, intentional chemistry is performed as ammonium dichromate is heated to decomposition to make chromium dioxide, which is used in the production of magnetic tape products. In the Upstream Feeds facility under study, physical processing is performed as ammonium dichromate is fed through a screw conveyor. The Preliminary Screening Method is to be used as a first-cut determination whether chemical reactivity hazards will need to be managed in the physical processing facility. 

A review of material safety data and standard references for the ingredients may result in answering Questions 7 through 11 as shown in Table 5.5. Two of the ingredients, aluminum powder and sodium hydrosulfite, are known to be reactive chemicals, so a chemical reactivity hazard is obviously present. At this point, the Preliminary Screening Method would point the user to the information in Chapter 4, for identifying and managing chemical reactivity hazards. 

The Preliminary Screening Method is not intended to identify all conditions under which reactive chemicals and incompatibilities may lead to uncontrolled reactions. However, it should give an indication whether chemical reactivity hazards exist, as well as what to investigate more closely by analysis and testing. 

---