The document discusses inherent safer design (ISD) principles in chemical processes, particularly focusing on the Flixborough accident, which resulted from a cyclohexane leak and caused significant casualties and property damage. It outlines strategies for accident prevention, including minimization of hazardous materials, substitution with less dangerous chemicals, moderation of hazards, and simplification of processes. Ultimately, it emphasizes designing chemical processes to eliminate hazards rather than relying solely on safety controls.

1. Name: Yogendra Singh
Year: 3rd Year
Roll No.: 1910043
Subject: DSE-5 Green Chemistry
Submitted To: Dr. Vijay Kumar

2. INDEX
Principle 12
Flixborough Accident
 Background Process
 The Accident
 Scale Of Accident
 Safer route to Cyclohexanol
Inherent Safer Design(ISD)
Subdivision Of ISD
 Minimization
 Substitute
 Moderate
 Simplification

3. Principle 12: Safer Chemistry
for accident Prevention
Substances and the form of a substance used in a
chemical process should be chosen to minimize
the potential for chemical accidents, including
releases, explosions, and fires. Working with
chemicals always carries a degree of risk.
However, if hazards are managed well, the risk
can be minimised. This principle clearly links with
a number of the other principles that discuss
hazardous products or reagents. Where possible,
exposure to hazards should be eliminated from
processes, and should be designed to minimise
the risks where elimination is not possible.

4. FLIXBOROUGH ACCIDENT
 Flixborough disaster was an explosion at
a chemical plant owned by Nypro (UK)
Ltd.
 Occurred in Flixborough, England on
Saturday, 1st June 1974 at about 4.53pm.
 The plant has been in operation since
1967.
 A temporary pipe containing cyclohexane
caught on fire and burst.
 The blast was equivalent to 15 tons of
TNT.

5. BACKGROUND OF PROCESS
The plant was built for the production of caprolactam, which is a basic raw material
for the production of Nylon 6. In this process, hot cyclohexane produced by selective
reduction of benzene was partially oxidized by compressed air. In this process,
benzene on hydrogenation gave cyclohexane which on aerial oxidation with
homogeneous cobalt catalyst resulted in 50% cyclohexanone and 50% cyclohexanol.
Since the conversion of cyclohexane to the product was low, so it was necessary co
circulate cyclohexane through six reactors arranged in series. This was done by
injecting O2 into cyclohexane at a working pressure of 9 bar and temperature of
155°C.

6. Simplified diagram of cyclohexane
oxidation plant before the accident

7. The Accident
Two months prior to the explosion,
cyclohexane was discovered to be leaking
from Reactor No. 5. It was decided that
Reactor No 5 to be removed for inspection
and a temporary bypass assembly to be
constructed to connect Reactor No.4 to No.6,
while repairs were made. At 4:53pm on 1st
June 1974, the temporary bypass pipe
ruptured. Within a minute, about 40 tons of
the cyclohexane leaked from the pipe and
formed a vapour cloud, that when coming in
contact with an ignition source, exploded and
completely destroying the plant.

8. Scale Of Accident
Casualties: 28 people were killed and
36 peoples were seriously injured.
All the records and charts for the start
up were destroyed.
The fire were remained burning in the
area for over 10 days.
The blast can be heard 30 miles away.
Property damage extended over wide
area. More than 1,800 buildings within
three miles radius of the site were
damaged.

9. Safe Route to cyclohexanol(ISD)
The safer ISD process used by Asahi does not produce flammable
cyclohexane and is more energy efficient. Atom economy is 100% as only
the required product cyclohexanol is obtained. It uses water and high-silica
pentasil zeolite as catalyst. This is ISD, as cyclohexane is not formed, which
was responsible for the accident. Cyclohexanol is an important
intermediate in the synthesis of nylon-6,6 via adipic acid and nylon 6 via
caprolactam. The methods of preparation are displayed in given diagram.

10. Inherent Safer Design (ISD)
This principle is also inherently safer chemistry for accident prevention.
Inherent safer design is defined as the design of chemical processes and
produces with specific attention to eliminate hazards from the
manufacturing process rather than relying on the control of their hazard.
Hazard and operability studies are done before designing a chemical
plant. This relies on mechanical safety devices and well-known procedures
to prevent hazardous occurrences. It has been observed that about 60%
of accidents occur due to mechanical failure or due to personal
operational errors. The concept of inherently safer design (ISD) redesigns
the process of manufacturing so that the hazardous product, which is
prone to accident, is not produced. The principle is 'what you don’t have,
can't harm you'.

11. Subdivision Of ISD
Minimization
Substitute/ Substitution
Moderation
Simplification

12. I) Minimization
Use small quantities of hazardous materials or reduce the size of equipment
operating under hazardous condition (e.g., high temperature,pressure). Change
from large batch reactors to a smaller continuous reactor for safety purposes should
be done. It is necessary not to store hazardous materials to avoid accidents. Use of
smaller quantities of hazardous materials, wherever possible, through just in time
production, is advised. For example:
 Nitro glycerine can be made in a continuous pipe reactor with a few kilograms of
inventory instead of a large batch reactor with several thousand kilograms of
inventory.
 Loop reactors have been used to reduce the size of chemical reactors in many
applications, including polymerization, ethoxylation and chlorination.

13. II) Substitute/Substitution
Along with minimization, substitution should also be considered as
an alternative. A hazardous material should be replaced with a less
hazardous or more benign chemical. Less toxic solvents should be
used. Water for heat transfer instead of hot oil should be used.
Coolant used should be non-reactive instead of water. For example:
An alternate synthesis chemistry for acrylic acid manufacture by
propylene oxidation eliminates the use of carbon monoxide, nickel
carbonyl, anhydrous hydrogen chloride and acetylene used in an
earlier process.
Water-based latex paints eliminate fire, toxicity and environmental
hazards associated with solvent-based paints.

14. III) Moderate
If it is not possible to substitute a hazardous material then one should focus on modifying the
properties of the hazard. Reduce hazards by dilution, refrigeration or process alternatives that
operate at less hazardous conditions. For example:
 Combustible solid was handled as a pellet instead of a fine powder, reducing the dust
explosion hazard.
 Off-site risks were reduced by replacing anhydrous ammonia with aqueous ammonia for a
neutralization application.
IV) Simplification
Eliminate unnecessary complexity and design user friendly plants. For example:
 Old piping was removed from a plant because of process modifications, making it impossible
to accidently transfer material into a reactor through that piping because of either operating
error or leaking valves.
 Confusing control system layouts, equipment on/off switches and equipment labelling in the
plant were simplified to reduce the potential for error.