This month our example is Diborane,
which has a chemical formula of
B2H6. Diborane is listed under the
UN # (United Nations Number) by the US Department of
Transportation: UN 1911 and has a CAS # of 19287-45-7.
Persons exposed only to Diborane gas
pose little risk of secondary contamination. Diborane is
a colorless highly flammable gas with a repulsive,
sickly sweet odor. At high concentrations, it ignites
spontaneously in moist air at room temperature. It
reacts with water to form hydrogen and boric acid.
Diborane vapors are heavier than air and may collect in
low-lying areas. Diborane is highly irritant when it
contacts moist tissues such as the eyes, skin, and upper
respiratory tract and can cause thermal burns. Burns are
caused by the exothermic reaction of hydrolysis.
It is generally shipped in
pressurized cylinders diluted with hydrogen, argon,
nitrogen, or helium. It mixes well with air and
explosive mixtures are easily formed. At high
concentrations, it will ignite spontaneously in moist
air at room temperature. The main toxic effect of
exposure to Diborane is irritation of the respiratory
airway, skin, and eyes.
Inhalation is the major route of
exposure to Diborane. An odor threshold between 2 and 4
ppm has been reported for Diborane, which is higher than
the OSHA permissible exposure limit (PEL) of 0.1 ppm.
Prolonged, low-level exposures, such as those that occur
in the workplace, can lead to olfactory fatigue and
tolerance of Diborane’s irritant effects. Odor does
not provide adequate warning of hazardous
Children exposed to the same levels
of Diborane as adults may receive larger dose because
they have a greater lung surface area:body weight ratios
and higher minute volume:weight ratios. In addition,
they may be exposed to higher levels than adults in the
same location because of their short stature and the
higher levels of Diborane found nearer to the ground.
Direct contact with concentrated
Diborane vapors may cause severe eye or skin burns,
leading to cell death and ulceration. Ingestion is
unlikely to occur because Diborane is a gas at room
gas at room temperature
properties: odor does not provide adequate warning
Molecular weight: 27.7
point: (760 mm Hg) = -135 °F (-92.8 °C)
Freezing point: -264.8
°F (-164.9 °C)
(liquid): 0.210 at 15 °C
pressure: @62°F: 39.5 atm
Density: @68°F: 1
solubility: Decomposes in water
Ignition temperature 104°F
Flammable Range: 0.8 %
to 88 % (concentration in air)
Diborane is produced by the reaction of lithium
hydride with boron trifluoride catalyzed by ether at 25
°C. Diborane is used in rocket propellants and as a
reducing agent, as a rubber vulcanizer, as a catalyst
for olefin polymerization, as a flame-speed accelerator,
and as a doping agent in the manufacture of
Synonyms include boroethane,
boron hydride, diboron hexahydride.
(recommended exposure limit) = 0.1 ppm
(immediately dangerous to life or health) = 15 ppm
ERPG-2 (maximum airborne concentration below which it is
believed that nearly all persons could be exposed for up
to 1 hour without experiencing or developing
irreversible or other serious health effects or symptoms
that could impair their abilities to take protective
action) = 1 ppm.
Incompatibilities Diborane is
incompatible with oxidizers, aluminum, halogens, and
Exposure The toxic effects of Diborane are primarily
due to its irritant properties. The local irritant
action of Diborane is due to the heat released as a
consequence of its reaction with water and products
formed by the hydrolysis reaction, such as boron oxide.
Symptoms may be apparent immediately or delayed for a
few hours. Children do not always respond to chemicals
in the same way that adults do. Different protocols for
managing their care may be needed.
Exposure to Diborane can cause a sensation of
tightness of the chest leading to diaphragmatic pain,
shortness of breath, cough, and wheezing. These signs
and symptoms, which may be delayed for up to 24 hours,
can be seen for 3 to 5 days after an exposure. Children
may be more vulnerable to gas exposure because of higher
minute ventilation per kg and failure to evacuate an
area promptly when exposed.
Skin irritation manifested as reddened skin may
occur from exposure to Diborane vapors.
High concentrations of Diborane can cause eye
irritation, pain, swelling, lacrimation, or photophobia.
Dizziness, headache, weakness, central nervous
system depression, and incoordination have been seen
following exposure to Diborane.
Sequelae Weakness and fatigue may follow exposure to
Diborane. Damage to liver and kidneys may occur in some
cases during metabolism and excretion.
Exposure Chronic exposure to low concentrations of
Diborane were reported to have caused seizures,
convulsions, fatigue, drowsiness, confusion, altered EEG
responses, and spasms of the voluntary muscles. Others
have reported headache, vertigo, chills, and sometimes
fever. Asthmatic bronchitis can also occur. Chronic
exposure may be more serious for children because of
their potential for a longer latency period.
Carcinogenicity Diborane has
not been classified for carcinogenic effects.
Reproductive and Developmental
Effects No information is available regarding
reproductive or developmental effects of Diborane in
experimental animals or humans. Diborane is not included
in Reproductive and Developmental Toxicants, a
1991 report published by the U.S. General Accounting
Office (GAO) that lists 30 chemicals of concern because
of widely acknowledged reproductive and developmental
In using the PEAC application we
access information for the chemical by first locating
Diborane in the database. The following figures show the
screens displayed for chemical properties, Figure 1 for
the PEAC-WMD for Windows application and Figure
2-5 for the PEAC‑WMD for the Pocket PC
Figure 1 - Using the Lookup
By: Name for Diborane
using the PEAC-WMD for Windows
Review of the information displayed
in the chemical properties screen whether in Figure 1
(above) or Figures 2-5 (below), show chemical properties
values discussed earlier at the top of this discussion.
As you can see below, the published toxicity values,
e.g., IDLH, ERPGs, and the TEELs (Temporary Emergency
Exposure Limits) published by Department of Energy are
provided. We will use the IDLH as the Level of Concern
when we develop the PAD a little later.
Figure 2 – Selecting Diborane
using the PEAC-WMD for Pocket PC application
Figure 3 – The top portion of the
Chemical Properties Data Display Screen
Figure 4– The middle portion of
the Chemical Properties Data Display Screen
Figure 5– The bottom portion of
the Chemical Properties Data Display Screen
The PEAC-WMD application provides
more than just the Chemical Properties for the
identified material, the Chemical Properties are
just the default information screen displayed, by
clicking (if running the Windows version, see Figure 6)
or tapping (if running the Pocket PC version, see Figure
7) on the drop-down box where Chemical Properties
is displayed on the screen, the user is provided with a
list of other databases that provide information for the
selected chemical (Diborane in our current example). So
the search is done once, and the user is indexed into
the different databases easily and quickly.
Figure 6 – Accessing other
databases from the PEAC-WMD for Windows
Figure 7 – Accessing other
databases from the PEAC-WMD for Pocket PC
A quick review or sampling of the
type of information available in each of these screens
is now provided. First is access to Respirators
Recommendations, these are primarily taken from the
NIOSH Pocket Guide and provide the user with different
types of respirators for increasing concentrations. A
sample of the information is provided in Figure 8.
One of the other databases provided
in the PEAC-WMD tool is access to Chemical Protective
Clothing (CPC). As shown in Figure 7 above, there was no
listing shown for Chemical Protective Clothing in the
list of databases available and the reason is that there
are no CPC entries in the PEAC-WMD database for
Diborane. The reason is that the CPC manufacturers have
not tested their products against Diborane. Then the
question is why not? The most likely answer is that
Diborane reacts with moisture to form Hydrogen and Boric
Acid. If using a full-face respirator that protects the
eyes and respiratory system as indicated in the
respirator database entries, then the minimal irritation
to the skin due to contact with Diborane vapors doesn’t
Figure 8 – Respirator
Recommendations for Diborane
|Figure 9 –
IC (Incident Commander) will typically utilize more than
a single resource for developing a response plan but
sometimes the information in other resources will use a
different name for the same substance. Clicking on the
selection will provide a quick list of
other names the substance may be referenced by in other
resources as shown in Figure 9. To further assist the
responder in initiating the best response plan, PEAC‑WMD
also provides the generic guidelines found in the
‘orange pages’ of the DOT Emergency Response Guidebook
(ERG). These are categorized into different types of
procedures depending on the incident and the problem to
be mitigated. An example for Spill or Leak
is shown in Figure 10.
|Figure 10 – ERG Spill or
Leak Response |
A benefit of using the PEAC tool is
assistance in the development of an evacuation zone for
those chemicals that produce a toxic vapor cloud.
Because of its boiling point Diborane will be released
from a container as a vapor or aerosol or a liquid that
will rapidly vaporize. As with all of our examples,
AristaTek creates a scenario for a spill or release of
the specific chemical, and then we work through the
development of a PAD (Protective Action Distance) to
demonstrate how the PEAC system works.
For our hypothetical scenario using
Diborane as the involved chemical we’ll set the location
to be a manufacturing facility located in Akron, OH. The
local fire department knows that the facility has
regular deliveries of Diborane cylinders to the facility
and that the cylinders are stored outside. The cylinders
are moved as needed from their storage location and this
movement can be during the day or night since the
production facility runs around the clock 24/7.
Developing plans for what might happen, the fire
department decides to take a look at what impact on
surrounding areas if an accident occurred during one of
these movements and the contents of a cylinder were
released. The HAZMAT Coordinator decides that they’ll
look at both a daytime (noon) and a midnight release.
They select a temperature of 85°F
and a date of July 1st and a wind speed of 2
mph with a clear sky for the daytime release. For the
nighttime release they select a temperature of 30°F, a
date of January 1st and a wind speed of 2 mph
and clear skies. In both cases they select an
urban/forest terrain type since the manufacturing
facility is located in an industrial section of the
city. The PEAC tool can provide guidance with regards to
toxic vapor clouds that are released.
If you decide to follow along as we
proceed through these examples, remember to set the
location to Akron and set the date and time to the
proper values, otherwise you’ll compute different
values. Also it should be understood that the examples
shown below assume that no explosion or fire is
involved, otherwise the Diborane would ignite and not
form a toxic cloud. In addition, the reader should also
understand that the PEAC-WMD system makes no allowance
for reaction of the Diborane with moisture in the air.
As seen at the top of the data
display screens, there is a yellow icon displayed; this
is the PEAC icon for notifying the user that a
Protective Action Distance can be calculated. Clicking
or tapping on the PAD icon will display a screen as
shown in Figure 11. Following through the screens, we
provide information on the Meteorology, Container Size,
and Type of Release (Source). The following figures
demonstrate how we would work through our two different
cases to see what effect they have on our Protective
It’s Akron in July and the
temperature about 85°, wind is set for 2 mph,
clear skies and the terrain is Urban/Forest
since it’s an industrial setting.
We have selected from our list
of container sizes the Cylinder selection.
We have selected a Large
Rupture for the type of release.
Figure 11 – Calculating a PAD using the
PEAC‑WMD System for daytime (July 1st)
By pressing the right arrow at the
top of the screen, the PEAC system will display a screen
as shown in Figure 12. This calculates a PAD
(Protective Action Distance) based on the default
Level of Concern the IDLH of 15 ppm. This
evacuation or standoff distance is based on the toxicity
Figure 12 – Default PAD for
on July 1 and using the IDLH of 15 ppm
Now we can re-evaluate but for a
night time release on January 1st around
midnight, winds of 2 mph and clear skies.
Now we set the temperature to
30°F and leave everything else unchanged.
We don’t need to change the
We leave the Large Rupture
as the Source type.
Figure 13 – Calculating a PAD using the
PEAC‑WMD System for nighttime (January
Figure 14 – Default PAD for
on January 1 and using the IDLH of 15
The obvious effect of nighttime
conditions and the associated stable atmospheric
conditions found at nighttime increase the size of the
PAD. The fire department now knows that for a single
cylinder of Diborane, a nighttime release is going to
affect a much larger area than a daytime release.
Substantial portions of this
discussion were adapted from the Agency for Toxic
Substances and Disease Registry (ATSDR) Web site for
Medical Management Guidelines at: http://www.atsdr.cdc.gov/.