PEAC® - the “what if” answer machine
A popular saying and one we
use many times within AristaTek is “sometimes you can’t see the forest for the
trees.” Our staff gets so busy sometimes working on a technical problem or new
feature for the PEAC tool or visiting with customers about the different
features of the PEAC tool, we forget to tell our audience the biggest
benefits. Why it is so easy and quick use and how it can be used as a “what
if” answer machine.
When the PEAC tool was
originally conceived back in early 1996, a prime objective was to simplify the
input process, i.e., number of steps required, by the operator to get useful
information so good sound decisions could be made. This result of this
original objective is demonstrated in two forms:
- How data or information
related to a hazardous substance is accessed and displayed.
- How the computational
tools are designed to make asking “what if” questions easier for the
We’ll discuss briefly the
first form, how the data is organized. There are different information systems
or software applications available in the market place. They typically have
similar information since most use many of the same references to construct
their databases. One of the problems the PEAC developers identified was the
available information for different hazardous substances. For a basic group of
substances, that are commonly used commercially, there are volumes of data
available from multiple sources. For some of these substances an individual
could generate in excess of 40 pages of information on a single substance.
This is a relatively small list of substances, which amount to a list of about
1200 to 1500 substances. Typically the reason there is so much information
available on these substances is because they are produced in such large
quantities or they are used in so many different applications or they are very
hazardous and require special handling.
The other 5+ million
substances found in reference sources have a much smaller amount of information
available for inclusion in a database. The reason there is limited information
varies, but typically it is because they are produced in relatively small
volumes or used in very specific processes or they may not be that hazardous if
persons are exposed to them. These may be valid reasons for the limited
information, but the responder to a spill of these substances still needs
access to basic information to help them make decisions.
The truth of the matter is
if a substance is used in few processes and quantities are limited to small
volumes, there isn’t much emphasis within the commercial market place to
investigate the toxicity of the substance or go to the expense of publishing
data or information regarding the substance. Many substances are produced in-house
at a manufacturing facility for a specific process and the manufacturer may
know its chemical and physical properties but the information and data aren’t
in the public domain.
A common example of this
fact is the limited information available from manufacturers of chemical
protective clothing (CPC) and specific testing of a garment product against a
wide assortment of products. The testing is expensive and therefore is
performed on the more common substances for which it might be required. In other
cases it may be tested against a specific substance because a customer needs
CPC products for personnel working with that specific substance. Once the
testing is done for the customer, it then becomes part of the manufacturer’s
But I’m digressing from the
original topic of dealing with varying amounts of information on substances.
The PEAC developers felt that information overload
was just as
dangerous or inhibiting to a responder as not having enough information. The
thought being who wants to wade through 10 or 20 pages of information to find
the specific piece of data or information needed while planning an operation.
The eventual concept was to
divide up the data or information into logical categories and allow the user to
select the specific logical piece they needed. This allowed the developers to
build the database with logical blocks of information that a user could digest
or find the piece(s) they needed quickly and easily to make their decisions.
Hence, this is why the data or information is broken into different portions;
we think logical portions, for a selected hazardous substance. Maybe when all
the information is assembled into a single document it is 20+ pages long, but
the user can quickly go to the piece they need without having to deal with all
The eventual solution, which
in retrospect seems obvious, was to have all those different portions or pieces
of information and data that are related to a selected hazardous substance
indexed for easy selection and display.
For an example, let’s assume
an incident involves the common chemical Anhydrous Hydrogen Chloride. The
responder only needs to identify that an incident involves Anhydrous Hydrogen
Chloride and then find the substance in the database. Now there are multiple
types of data or information available at the click of a mouse button. To
begin with, the default display that is provided to a user once a substance is
found in the database is the Chemical Information selection (Figure 1). This
provides the responder with basic information on the substance and what to
expect when it is released from its container.
For instance, the header on
the display will provide the substance name, CAS#, UN#, and DOT ERG guide
number and name. The ERG guide number and name are in the form of a hyperlink
that when clicked will display the information from the orange pages of the ERG
and the green pages entry if there is a PAD recommendation.
Chemical Information display will provide the NFPA hazard rating (NFPA 704, Standard System for the Identification
of the Hazards of Materials for Emergency Response)
for the chemical in the form of the NFPA HAZMAT
diamond that all responders certified at Awareness Level or higher recognize as
per NFPA 472. The NFPA HAZMAT diamond graphic indicates immediately that the
substance presents a significant health hazard and is slightly unstable when
Scrolling down the Chemical
Information display the user will see data for chemical and physical
properties. If the material was flammable, which Anhydrous Hydrogen Chloride
is not, then values for auto ignition temperature, flash point, LEL and UEL
would be provided. The boiling point of -121°F tells the responder this
substance will be a vapor at normal temperatures and the vapor density of 1.3
will signal that it is heavier than air, which is noted next to the vapor
density. The vapor pressure of 40+ atm (atmospheres) should be an indication
that this material is probably shipped as a liquefied gas under its own vapor
pressure and the container is probably at a very high pressure. This
information is already shown just below the header information at the top of
the display. The toxicity values indicate just how much of a health hazard the
substance can be. The NFPA 704 health hazard rating was 3 and the IDLH is 50
So very quickly the
responder knows, the material is a vapor at normal temperatures, shipped as a
liquefied gas (high pressure), it’s not flammable, its vapor is very toxic, the
vapor will seek low spaces and it may be unstable when heated. This process
takes just seconds and now we’re ready to learn more.
Figure 1 – Chemical Information display for Anhydrous Hydrogen Chloride
To find additional
information, the user clicks on the data selection field to display the data
selection options for the hazardous substance Figure 2.
Figure 2 – Data selection options for Anhydrous Hydrogen Chloride
At this point the responder
has the option to view CPC garments tested against Anhydrous Hydrogen Chloride,
recommended types of respirators based on the concentration, symptoms of
exposure, reactivity information, DOT ERG procedures on dealing with this type
of substance, or other reference sources that describe Anhydrous Hydrogen Chloride
such as the NIOSH Pocket Guide or the CHRIS Manual.
One of the most powerful
features is the availability of the User Data, which allows the user to
customize the PEAC tool for their particular needs. The user can create or
import data of their own choosing and access it via the PEAC tool interface.
Therefore, SOPs, response plans, points of contact, MSDS’s, DECON procedures,
and many other types of information can be incorporated into the PEAC tool
structure for easy access when needed.
Any of these topics are just
a click away at this point. Any of the data or information displayed on the
right side of the main display window can be printed to the local printer for
dissemination to other personnel.
The other aspect I’d like to
quickly discuss is asking the PEAC tool “what if” questions.
Dr. John Nordin has touched
on this topic in some of his technical articles in the past but I’d like to
cover some of the same ground again. Sometimes when a responder arrives on
scene where there is a hazardous substance release, the specifics of what has
happened are not obvious. The responder may be prevented from observing the
full details because of obstacles obstructing the view, fire and smoke, or
hazardous chemical vapors preclude close inspection. As information related to
the incident becomes available, a clearer picture will be formed and the
operations plan may be changed as the incident evolves.
Because the AristaTek
founders were involved in earlier field research projects at the Nevada Test
Site studying vapor dispersion, the plume modeling feature of the PEAC tool
received considerable thought and design attention. As everyone knows, vapor
clouds don’t wait for anybody, therefore the PEAC plume model was designed to
allow the user to make quick assumptions and develop information quickly. The
sooner an exclusion zone or protective action distance can be determined, the
sooner the public can be warned and actions taken to protect them.
The PEAC PAD Calculator is
designed to allow the user to do as many “what if” calculations as required
ensuring all possible outcomes have been assessed and considered. An example
might be arriving at a scene involving a train derailment of tank cars and
there is a fire involved. Perhaps Anhydrous Hydrogen Chloride is identified as
one of the derailed tank cars but it’s unclear if the tank is leaking or if
it’s close to the involved fire.
In this situation the
responder can do some quick “what if” calculations and develop some answer very
quickly. Then as the full description of the scene becomes clear, the answers
can be refined as needed.
First, it might be best to
assume a worst-case condition that the tank car of Anhydrous Hydrogen Chloride
is not breached but may be close enough to the fire that the contents may
become unstable or the tank could BLEVE releasing the contents as an
instantaneous release or puff. Referring back to Figure 1 or 2, we see the PAD
displayed at the right end of the row of icons at the top of the window under
the menu options. This means the PEAC tool has enough data to run the plume
model and compute a protective action distance (PAD) or exclusion zone.
The PEAC tool provides two
methods to operating the plume model; one method allows input of container
types or sizes and then a description of the source or type of release. The
other method allows the user to specify either a continuous release or an
instantaneous release where the user provides a flow rate or amount released as
a puff. To signal the application which mode will be used requires simply
clicking an option box on the options window that is accessed off the Edit menu
selection. To demonstrate how both modes work, we’ll do the instantaneous or
puff release using the second method described above.
To start the plume model
input sequence, click on the PAD icon [
]. The input and results windows are
represented in Figures 3-5.
Figure 3 – Meteorology input
Figure 4 – Specified Source
Figure 5 – Results window
For those users familiar
with the PEAC tool, we’ve used Denver as the location and a date of March 22
and a time of 5:15 PM. In Figure 3 we used a Terrain value to describe the
surrounding surface cover as crops or low-level brush. In Figure 4 we have
selected the instantaneous release (puff) and an estimated mass of Anhydrous
Hydrogen Chloride at 150,000 lbs or about 75 tons. The results window as shown
in Figure 5 calculates a PAD of just over 4 miles and an initial isolation
distance in all directions of 1200 feet, which is based on a Level of Concern
of 50 ppm (the IDLH). In a time span of less than 60 seconds, we now have a
worst-case exclusion zone to protect any of the public if the Anhydrous
Hydrogen Chloride should be adjacent to the fire and BELVE. When we exit the
results window (Figure 5) a PAD Results report is generated which can be
printed or recalled later.
With some additional thought
we realize maybe we don’t have all our bases covered. The time is 5:15 PM and
it’ll soon be dark and everyone knows that once the sun goes down, we could run
into more stable atmospheric conditions, which can impact the resulting PAD.
But we can very quickly cover that situation by changing the time and rerunning
the plume model. We leave all input values the same but now we come up with a
considerable larger PAD because the more stable conditions cause the vapor
cloud to disperse at a slower rate as depicted in Figure 6.
Now we have the day and
night worst-case conditions but we still need to take a look at a couple of
other possibilities. Perhaps the Anhydrous Hydrogen Chloride tank car has been
breached and is leaking. What’s a reasonable exclusion zone to establish?
Let’s assume there is a 1”
hole near the bottom of the tank car, what effect does this change have on our
This time we will change the
plume modeling mode to use the container size input and allow the user to
describe the release type with the release time still 5:15 PM. The input
windows are shown in Figure 7-9.
Figure 6 – PAD results for
Figure 7 – Meteorology input
Figure 8 – Container selected is
railcar with default values
Figure 9 – Source type is hole
described as 1” at bottom of the container
The results are shown in
Figure 10, which predicts a PAD of 2.5 miles for the 5:15 PM time.
Depending on how long it
will take to plug the leak, it seems likely the incident will last into the
night, so we need to check the PAD Calculator for a night release through the
1” hole. We selected a time of 8:15 PM and stepped back through the input
windows to arrive at a new exclusion zone. That value is shown in Figure 11
and predicts a PAD greater than 9.5 miles.
Based on these values and
location of the surrounding population, decisions can be made as to
recommendations for either evacuation and/or shelter-in-place.
Figure 10 – PAD Calculator results
at 5:15 PM
Figure 11 - PAD Calculator results
at 8:15 PM
The user can do these “what
if” questions very rapidly and print off the results for reference as
conditions change. Likewise, the individual PAD Results reports can be
recalled later as needed. Useful documentation is at your fingertips when you
As the incident develops the
responder can change those input values that are different and refine the
results just as quickly as these four evaluations were made.
If readers have questions or
suggestions, please direct them to firstname.lastname@example.org or give us a call at