Chemical Engineering January 2022 - 35

The definition of acceptable risk
varies from company to company.
Each
organization
must
define
what is appropriate for it, which is
a difficult task at best. If the question
were simply financial, such as
weighing the cost of risk reduction
against the monetary loss of an incident,
it would be fairly straightforward
to answer. The difficulty arises
when one has to consider the loss
of life or personal injury. What is a life
or severe injury worth? What is an
acceptable fatality rate? These are
hard questions to answer.
In a recent article about COVID-19,
Alex Berezow discussed the value of
life [3]. Although he wrote the article
from a geopolitical perspective, his
remarks apply equally to HSE. He
states there are three ways to view
the value of life: morally/philosophically,
economically and a blend of
the two.
" Many people say that one cannot
put a price tag on human life. This
is true from a moral or philosophical
perspective. ... In the eyes of an
economist, however, we are neither
equal nor invaluable.
" How does one begin to put a
price tag on a human life? A simple
thought experiment demonstrates
how easy it is. Pretend that you're
the mayor of a small town. There's
a dangerous intersection that results
in one car crash fatality every year.
A company approaches you with a
solution: By redesigning and rebuilding
the intersection, it can guarantee
no more car crashes. The only problem
is that the infrastructure project
costs $100 million. Considering that
your small town's budget is far less
than that, the city couldn't afford it
without a massive tax increase. You
propose that tax increase to your
citizens, who reject it overwhelmingly.
The citizens have spoken: The
lives of those who will be killed in accidents
at the intersection are not
worth $100 million.
" ... For what it's worth, various U.S.
government agencies value a life between
$9 million and $10 million.
" The key is to remember that we
are talking about economic value
rather than moral value. There is always
space for a moral consideration
in geopolitics, but it too must be considered
along with
other factors. "
When thinking
about risk, engineers
should also
consider the information
shown in
Tables 1 and 2, as
well as their own
company's data
and practice.
Type of
incident
Fire
Explosion
Toxic release
TABLE 1*. TYPES OF CHEMICAL PLANT INCIDENTS
Probability
Fatality
potential
High
Intermediate
Low
Low
Intermediate
High
Economic
loss potential
Intermediate
High
Low
*Adapted from Table 1-6 in Crowl and Louvar, Chemical Process Safety, 3rd ed. [9]
TABLE 2. COMPARATIVE FATALITY DATA
Fatality cause
Methodology
The methodology
presented here will
help to find and
assess HSE hazards
during process
synthesis. For
hazards that could
result in serious or
catastrophic incidents, the engineer
should consider changing the
basic process to make it inherently
safer. Because synthesis is the time
when the process is being created,
it is the ideal time to explore options
for hazard elimination or mitigation.
During synthesis, one need not
work on routine safety issues, such
as pressure relief. Later on, detailed
studies, such as HAZOP (hazard
and operability analyses), will identify
these issues.
The steps in the methodology are
the following:
* Identify the hazards
* Estimate the potential for loss
* Estimate the probability of having
an incident
* Identify the major risks
* Consider inherently safer designs
Step 1: Identify process hazards.
Begin by looking for toxic release, explosion
and fire hazards, as follows:
* Hazardous materials. For each
flow stream in the process, list
the composition, materials and
amounts of each stream. This
should include intermediates
and impurities. Consider feed
streams, products, byproducts,
recycle streams, purge, catalysts
and solvents, as well as
planned discharges to sewers,
the atmosphere, landfills,
recyclers
and waste disposal firms.
For each substance, determine
whether it is hazardous; and if
so, the degree of hazard it presCHEMICAL
ENGINEERING WWW.CHEMENGONLINE.COM
JANUARY 2022
Smokers who smoke ≥15/d ( 2005-2009)a
Car travel (2019) b
U.S. Manufacturing (2018) c
Chemical Manufacturing (2018) c
Being struck by lightning (2006-2019) d
Source data:
ª 2014 Surgeon General's Report, Table 12.4, p. 660
b National Safety Council
c Bureau of Labor Statistics
d National Weather Service
ents. One needs to consider
health, flammability, instability
and special hazards. An example
of a material having a special
hazard is MIC, which reacts violently
with water. This is believed
to be the initiating cause of the
Bhopal incident mentioned previously.
Usually, the National Fire
Protection Association (NFPA;
Quincy, Mass.; www.nfpa.org)
or the U.S. Hazardous Materials
Identification System (HMIS)
ratings are sufficient sources
of information to determine the
hazard level of a chemical. Both
systems have five rating levels.
Table 3 explains the NFPA levels.
HMIS is similar.
* Process-related hazards. Some
operating features and equipment
in a process may be hazardous.
The most common are
runaway reactions,
high temperatures,
high pressures (or
vacuum) and large inventories of
hazardous materials.
❍
Runaway reactions. Runaway
reactions are a fairly common
problem. High heats of reaction
and large reactor volumes
increase the probability
of an incident. If a reaction
is exothermic, assess the
chances that it could get out
of control. This usually occurs
when there is a problem,
such as a cooling system
or power failure. An assess35
Deaths
per 100,000
people
1,000
12
2.2
1.2
0.07
http://www.nfpa.org http://WWW.CHEMENGONLINE.COM
Chemical Engineering January 2022

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