Questions cont'd - doe-hdbk-1101-20040024

DOE-HDBK-1101-2004

If a plant has only one process covered by the Rule, must the PSM Rule be applied

to all process areas in the plant?

No. A plant may have some process areas that are covered by the PSM Rule and others

that are not. PSM provisions are invoked for covered processes only. However, DOE

contractors may choose to implement certain PSM elements in areas not covered by the

Rule if they believe activities in these areas pose a significant hazard. To avoid

regulatory confusion, contractors should document those parts of their plants that are

covered processes.

Can a facility contain more than one process?

A facility can contain several processes. If multiple processes are interconnected, they

may be considered a single process under the PSM Rule.

To determine whether a process is covered, should DOE contractors compare the

OSHA TQ for an HHC to the amount of the chemical annually consumed by the

process, or to the maximum intended inventory?

DOE contractors should determine whether a process is covered based on the maximum

intended inventory that the process can contain (tank or vessel capacity plus

interconnected piping capacity), rather than on its cumulative, annual use. Contractors

who wish to maintain the quantity of an HHC below its TQ limit, in a process capable of

containing over the TQ, must be able to demonstrate that they have effective measures in

place to ensure that the inventory in the process cannot exceed the TQ.

Several HHCs are listed in Appendix A along with a minimum threshold

concentration. What is the technical basis for the list and these thresholds?

The Appendix A list was drawn from several sources, including lists prepared by States

that have enacted similar regulations. In determining TQs and threshold concentrations

for the Appendix A HHCs, OSHA used an approach similar to that used by the State of

Delaware. For example, in evaluating toxic materials, OSHA assumed a ground-level,

continuous, steady state release for 1 hour. They also used neutrally buoyant Gaussian

dispersion modeling with a 4.3 m/s (14.1 ft/sec) wind speed, D-class stability, and urban

dispersion coefficients. The preamble to the PSM Rule discusses all of the specific

assumptions used by OSHA for its technical basis for toxic and reactive materials in

Appendix A.

In developing its Recommendation for Process Hazards Management of Substances with

Catastrophic Potential, the Organization Resources Counselors, Inc. (ORC) compiled a

list of dangerous toxic substances from a number of hazardous substance lists. This

compilation was then ranked by calculating the substance hazard index (SHI) for specific

concentrations. The SHI is defined as the substance vapor pressure (in mm Hg) at 20 oC

multiplied by 1,000,000, divided by 760, and divided by an acute toxicity concentration

for the substance. The priority cutoff for the list of toxins in ORC's recommendations

was 5,000. To be consistent with the technical basis for toxic materials submitted by

ORC to OSHA, the threshold concentration listed in Appendix A should correspond to an

SHI of 5,000. Where the concentrations specified for HHCs do not correspond, they

reflect judgments made by OSHA during the rulemaking process.