acquisition of the chemical to its final safe disposal should be in place before the experiment begins. The amounts of materials used and the names of the people involved in the laboratory work should be included in the written summary and recorded in the laboratory notebook.

The planning process may determine that area monitoring and/or medical surveillance is necessary for ensuring the safety of the experimenters. Such a determination is likely to be made only when there is reason to believe that exposure levels for the substances planned to be used in an experiment could exceed OSHA-established regulatory action levels or similar guidelines established by other authoritative organizations. It would be prudent to review the amounts of material to be used, the toxicological properties of the substances, the opportunity for and duration of exposure, and plans for waste disposal for any experiment plans involving highly hazardous chemicals.

5.D.3 Designated Areas

Most experimental procedures involving highly toxic chemicals, including their transfer from storage containers to reaction vessels, should be confined to a designated work area in the laboratory. This area, which could be a hood or glove box, a portion of a laboratory, or the entire laboratory module, should be recognized by everyone in the laboratory or institution as a place where special precautions, laboratory skill, and safety discipline are required. Conspicuous signs should clearly indicate which areas are designated. It is not necessary to restrict the use of a designated area to the handling of highly toxic chemicals as long as laboratory personnel are aware of the nature of the substances being used and of the precautions that are necessary, and have been trained appropriately for emergency response. It may also be prudent to post relevant Laboratory Chemical Safety Summaries (LCSSs) outside the laboratory door.

The laboratory supervisor should determine which procedures need to be confined to designated areas. The general guidelines (section 5.C) for handling hazardous chemicals in laboratories may be sufficient for procedures involving low concentrations and small amounts of highly toxic chemicals, depending on the experiment, the reagents, and their toxicological and physical properties.

5.D.4 Access Control

Only persons who are directly involved in the laboratory work and who have been advised of the special precautions that may apply should have access to laboratories where highly toxic chemicals are handled. Administrative procedures or even physical barriers may be required to prevent unauthorized personnel from entering these laboratories.

The use of locks and barricades may be appropriate to limit access to unattended areas where large amounts of highly toxic materials are being handled routinely or stored. However, it is important that locks not prevent emergency exits from the laboratory or hinder entrance for emergency response. Locks are generally more appropriate for securing storage areas and unattended laboratories than for preventing access to laboratories in which toxic chemicals are being actively used.

Some long experiments involving highly toxic compounds may require unattended operations. In such cases, securing the laboratory from access by untrained personnel is essential. These operations should also include fail-safe backup options such as shutoff devices in case a reaction overheats or pressure builds up. Additionally, equipment should include interlocks that shut down experiments by turning off devices such as heating baths or reagent pumps, or that close solenoid valves if cooling water stops flowing through an apparatus or if airflow through a fume hood becomes restricted or stops. An interlock should be constructed carefully in such a way that if a problem develops, it places the experiment in a safer mode and will not reset even if the hazardous condition is reversed. Protective devices should include alarms that indicate their activation. Security guards and untrained personnel should never be asked or allowed to check on the status of unattended experiments involving highly toxic materials. Warning signs on locked doors should list the trained laboratory workers who can be contacted in case an alarm sounds within the laboratory.

5.D.5 Special Precautions for Minimizing Exposure to Highly Toxic Chemicals

The practices listed below help build the necessary multiple lines of defense to enable laboratory work with highly toxic chemicals to be conducted safely:

  1. Procedures involving highly toxic chemicals that can generate dust, vapors, or aerosols must be conducted in a hood, glove box, or other suitable containment device. Hoods should be checked for acceptable operation prior to conducting experiments with toxic chemicals. If experiments are to be ongoing over a significant period of time, the hood should be rechecked at least quarterly for integrity of flow. Hoods in continuous or long-term use with toxic materials



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