PHA

1. Preliminary Hazard Analysis

2. Preliminary Hazard Analysis
 DERIVATION SOURCE - U.S military
standard of system safety program
requirements
 MAIN FOCUS - hazardous material and
major process area of plant
 TIME OF CONDUCTION - development
stage of process

3. Basic Elements
 Hazardous properties of raw material ,
intermediates, catalysts, waste products, bye
products and final products
 Plant equipment and operating environment
 Interfaces between components
 operating procedures and facility layout
 fire protection and safety environment

4. Procedure
 identification of hazards
 finding out the root cause
 major effects
 hazard category
 corrective/ preventive measures

5. Hazard Category
 NEGLIGIBLE
 MARGINAL
 CRITICAL
 CATASTROPHE

6. WHAT IF ANALYSIS TABLE FOR DAP PROCESS
PROCESS : DAP REACTOR DATE:
TOPIC INVESTIGATED: TOXIC RELEASES ANALYSTS:
Mr.
Ms.
WHAT IF CONSEQUENCE SAFEGUARDS RECOMMENDATIONS
THE WRONG FEED
MATERIAL INSTEAD
OF PHOSPHORIC
ACID?
POTENTIALLY
HAZARDOUS ACID
OR AMMONIA
REACTIONS WITH
CONTAMINANTS,OR
PRODUCTION OF
OFF-
SPECIFICATION
PRODUCT
Reliable vendor
&Plant material
handling
procedures
Ensure adequate
material handling
and receiving
procedures and
labeling exist
The phosphoric acid
is too low?
Unreacted NH3
carry over to the
dap storage and
release to the work
area
Reliable vendor
&NH3 detector
and alarm
Verify phosphoric
acid concentration
before filling storage
tank
The phosphoric acid
contaminated
Potentially
hazardous
phosphoric acid or
NH4 reactions with
contaminants or
production of off-
specification
product(s)
Reliable vendor
&Plant material
Ensure adequate
material handling
and receiving
procedures and
labeling exist

7. TABLE 6.6 sample page from the pha table for the h2s
AREA: h2s storage meeting date : 03/17/93
DRAWINGS: none analyst : R.u safe
HAZARD CAUSE MAJOR
EFFECYS
HAZARD
CATEROGY
CORRECTIVE/PREV
ENTIVE MEASURES
toxic release H2S storages cylinder
rupture
H2S not completely
reacted in process
potential for
fatalities from large
release
potential for
fatalities from large
release
4
3
provide warning
system
minimize on site
storage
develop procedure for
cylinder inspection
design system to collect
and destroy excess H2S
design control system
to detect excess H2S and
shut down process
Develop procedures to
ensure availability of
excess destruction
system prior to plant
start up

8. PROCESS: DAP REACTOR
ANALYSTS : Mr. Safety, MS OPERA
TOPIC INVESTIGATED: TOXIC RELEASES DATE: 05/13/07
WHAT IF CONSEQUENCE/HAZAR
D
SAFE GUARDS RECOMMENDATIONS
The wrong feed
material is delivered
instead of phosphoric
acid?
potentially hazardous
phosphoric acid reactions
with contaminants or
production of off specification
product
reliable vendor Ensure adequate material
handling and receiving
procedures and labeling exist
The phosphoric acid
concentration is too
low?
Unreacted ammonia carry
over to the dap storage tank
and release to the work area
reliable vendor
ammonia detector
and alarm
Verify phosphoric acid
concentration before filling
storage tanks
the phosphoric acid is
contaminated
potentially hazardous
phosphoric acid or ammonia
reactions with contaminants
or production of off-
specification product
reliable vendor
plant material
handling procedures
Ensure adequate material
handling and receiving
procedures and labeling exist
valve b is closed or
plugged
Unreacted ammonia carry
over to DAP storage tank and
release to the work area
periodic
maintenance
ammonia detector
and alarm flow
indicator or
phosphoric acid line
Alarm shutoff of ammonia
(valve A) on low flow
through valve B
Too high a proportion
of ammonia is supplied
to the reactor?
unreacted ammonia Cary over
to the DAP storage tank and
release to the work area
flow indicator in
ammonia solution
line ammonia
detector and alarm
Alarm shut off of ammonia
(valve A) on high flow
through valve A

9. EXAMPLE
Consider a design concept that feeds h2s
from a cylinder to a process unit. at this stage of
the design , the analyst knows only that this
material will be used in the process , nothing
more . The analyst recognizes that h2s has toxic
and flammable properties, and the analyst
identifies the potential release of h2s as a
hazardous situation. The analyst lists the
following causes for such a release….
 The pressurized storage cylinder leaks or ruptures
 The process does not consume all of the h2s
 The h2s process supply lines leak/rupture
 A leak occurs during connection of a cylinder to
the process

10. The analyst then determines the effects of these
causes. in this case , fatalities could result from
large releases. The next task is to provide
guidance and design criteria by describing
corrective/preventive measures for each
possible release. For example, the analyst
might suggest that the designer:….
 Consider a process that stores alternative, less toxic
materials that can generate h2s as needed
 Consider developing a system to collect and destroy
excess h2s from the process

11.  Provide a plant warning system for h2s releases
 Minimize on-site storage of h2s, without requiring
excessive delivery/handling
 Develop a procedure using human factors engineering
expertise for storage cylinder connection
 Consider a cylinder enclosure with a water deluge
system that is triggered by h2s leak detection
 Locate the storage cylinder for easy delivery access,
but away from other plant traffic.