ERT 312SAFETY & LOSS PREVENTION IN

BIOPROCESS

ACCIDENT INVESTIGATIONS

Prepared by:Pn. Hairul Nazirah Abdul Halim

Objective

• To discuss the method to investigate the accidents in the plant

• To analyze & evaluate in a case studies

Introduction

• The investigation of accidents and near misses provides opportunities to learn how to prevent similar events in the future.

• Accident investigation includes detailed descriptions and recommendations of the events.

Sub-topic

• Learning from accidents• Layered investigations• The investigation process• Investigation Summary• Aids for diagnosis• Aids for recommendation

Learning from accidents

• Build an investigation team• Every member learns about problems that

precipitate accidents• To avoid similar situations in the future• Learn how to prevent future accidents.

Learning from accidents• Fundamental step in accident investigation:

1. Developing a detail description of the accident2. Accumulating relevant facts3. Analyzing the facts and developing potential

causes of the accident4. Studying the system & operating method

relevant to the potential causes of the accident5. Developing the most likely causes6. Developing recommendations to eliminate

recurrence of this type of accident7. fact-finding not fault-finding.

Layered Investigations

• First layer: immediate technical recommendations, • Second layer: recommendations to avoid the

hazards, • Third layer: recommendations to improve the

management system.

Example 12-1

Illustrate the layered investigation process to develop underlying causes of a municipal pool accident.

A drowning accident occurred during an open swim period. Approximately 100 children, ranging between 5 and 16 years old, were in and around a pool (3 ft to 9 ft deep). An older child unknowingly pushed a 5-year-old into the deep water. The pool was relatively crowded, and the 5-year-old slipped under the water without being noticed by others, including the lifeguard.

Solution

The facts uncovered by an investigation team are

1. the pool did not have deep and shallow markings,

2. the older child was engaged in horseplay,

3. the younger child did not know how to swim,

4. the lifeguard had many blind fields of vision,

5. the pool was overly crowded,

6. the pool did not have an orientation program, and

7. the pool did not offer swimming lessons.

First layer recommendations: Immediate technical recommendations

1. Paint pool depths at the pool edges.

2. Add more lifeguards.

3. Reduce the number of swimmers.

Second layer recommendations: Avoiding the hazard

1. Prohibit horseplay.

2. Zone pool to keep smaller children at shallow end of pool.

3. Add swimming lessons for all age groups.

4. Give all new swimmers (especially young children) a pool orientation.

5. Add a roving lifeguard to monitor and control pool behavior.

Third layer recommendations: Improving the management system

1. Train lifeguards to alert supervision of observed potential problems.

2. Assign the supervisor to make formal (documented) audits on a regular basis.

Investigation Process

Steps

(1) Investigation team – choose team

(2) Brief survey – make overview survey to understand the type and information needed to derive causes of the accident.

(3) Set objectives and delegate responsibilities – based on (1) and (2)

(4) Preincident facts

- gather & organize preincident facts. Use flowsheets, procedures, photograph

Investigation ProcessSteps

(5) Accident facts

- make detailed examinations with photos, inspections.

- record extent of damage, hypothesize the sequences of event, cause of accident

(6) Research and analyses

– initiate research-type experiments & analyze facts

(7) Discussion, conclusions and recommendations

- study (2) to (6) to develop conclusion & layered recommendations.

(8) Report

- develop accident investigation report.

Accident Investigation Report• format should be flexible and designed specifically to

best explain the accident. • The format may include the following sections:

(1) introduction,

(2) process description (equipment and chemistry),

(3) incident description,

(4) investigation results,

(5) discussion,

(6) conclusions,

(7) layered recommendations.

Investigation Summary

• Summarizes the events and recommendations in a diagram

Aids for Diagnosis

• The data collected during accident are studied and analyzed:

- to find the cause of accident

- to develop recommendations to prevent a recurrence

• Sometimes, the evidence needs added analysis to uncover explanations.

• Require special techniques or aid to diagnosis to relate the evidence to specific cause.

Aids for Diagnosis

a) Fire

b) Explosions

c) Sources of ignition in vessel

d) Pressure Effects

e) Medical Evidence

Aids for Diagnosis

a) Fire

- identification of the primary source of ignition is one of the major objectives of investigation.

- For example;

- the depth of wood charring is proportional to the duration of burning

- most woods burn at a rate of 1.5 in/hr.

- If the time of extinguishment is known;

- If the depth of char at various locations is known;

- the region of the origin can be approximated.

Aids for Diagnosis

b) Explosions

- The classification of the explosion as either deflagation or a detonation & magnitude of the explosion may be useful to develop causes and recommendations.

Aids for Diagnosis

b) ExplosionsDeflagration-The pressure increases during deflagration:

for hydrocarbon-air mixtures

for hydrocarbon-oxygen mixtures

P1 and P2 = upstream & downstream pressure, respectively

81

2 p

p

161

2 p

p

Aids for Diagnosis

b) Explosions

Detonations

-In a single vessel detonations increase pressures significantly:

201

2 p

p

Aids for Diagnosis

c) Pressure Effect

- Investigation on ruptured pipe and vessel

- important to know the pressures required to create the damage

- Pressure necessary to produce a specific stress in a vessel depends on:

1. thickness of the vessel

2. vessel diameter

3. mechanical properties of the vessel wall

• For cylindrical vessel (pressure p < 0.385SM)

• For cylindrical vessel (pressure p > 0.385SM)

Where: p is the internal gauge pressure,SM is the strength of the material,tV is the wall thickness of the vessel, r is the inside radius of the vessel.

• For spherical vessel (pressure p < 0.665SM)

• For spherical vessel (pressure p > 0.665SM)

Example 12-3

Determine the pressure required to rupture a cylindrical vessel if the vessel is stainless 316, has a radius of 3 ft, and has a wall thickness of 0.5 in.

Solution• Because the pressure is unknown, Equation 12-4 or

12-5 is used by trial and error until the correct equation is identified.

• Equation 12-4 is applicable for pressures below 0.385SM.

• SM for Stainless Steel 316 (from Table 12-3) = 85,000 psi, 0.385SM = 32,700 psir = 3 ft = 36 in tv = 0.5 in.

Therefore Equation 12-4 is applicable, and a pressure of 1170 psi is required to rupture this vessel.

Example 12-4

Determine the pressure required to rupture a spherical vessel if the vessel is stainless 304, has a radius of 5 ft, and has a wall thickness of 0.75 in.

Solution• Equation 12-6 is applicable if the pressure is less

than 0.665SM

• SM for Stainless 304 = 80,000 psi

• 0.665 SM = 0.665(80,000) = 53,200 psi.

• Using Equation 12-6 for spherical vessels,

• The pressure criteria is met for this equation. • The pressure required to rupture this vessel is

1990 psi.

(d) Medical Evidence• Medical examinations of the accidents victims may

be useful for identifying the source of accidents• Type of medical data:

1. type & level of toxic in the blood2. location & magnitude of injuries3. type of poisoning (CO, toluene, etc.)4. sign of heat exposure5. sign of eye irritation

Aids for Diagnosis

Aids for Recommendations

• To develop recommendations to prevent a recurrence

• To prevent similar accident within the company / industry

Aids for RecommendationsControl Plant Modifications• Often not given the same attention/concern as a new

plant design• Many accidents are result of plant modifications• Recommendations to prevent this problem:

a) All modification must be authorized.b) The modification design should have same quality of pipes/equipments as the original designc) Safety review – HAZOP must be conducted while the modification project is in the design phase.d) Training – operators & engineers: to understand the modified operatione) Audit – to ensure the modifications are made &

maintain as designed.

User Friendly Design• Not create hazardous conditions• For example:

1. using nontoxic and nonflammable solvent

2. keep temperatures below the flash point & boiling point at atmospheric conditions

3. keep inventories low

4. design for safe shutdown during emergency situations

Block Valves• Install throughout plants to return a process to a

safe condition under unusual circumstances• Block valves are often controlled on the basis of

analyzer results for:

1. detecting solvent leaks

2. reactor analyzer – detect runaway reactions

(block valve can be opened to add a reaction inhibitor)

3. sewer analyzer – detect high concentration of contaminants

• Preventive Maintenance

- failure of emergency protection equipment such as cooling water pumps, instruments and deluge system can cause major accident.

- Protective equipments failed due to no preventive maintenance

- Preventive maintenance programs must be organized, managed & fully supported by management.

- Must have maintenance schedule

ERT 312/4 – SAFETY & LOSS PREVENTION

PBL PROJECT- INDUSTRIAL ACCIDENTS

Industrial Accidents

Group A1 & B1:  Flixborough Works Accident, June 1974

Group A2 & B2: Bhopal, India Accident, December 1984

Group A3 & B3: Seveso, Italy Accident, July 1976

Group A4 & B4: Thailand Toy Factory Fire, May 1993

Group A5 : Three Mile Island Nuclear Disaster, 1979

Group A6 & B6: Tokaimura Nuclear Disaster, September 1999

Group A7 & B7: Piper Alpha Incidents, July 1988

Prepare an Accident Investigation Report. The format may include the following sections:

(1) Introduction(2) Process description (equipment and chemistry)(3) Incident description: chronology of event,

cause of accident, extent of damage(4) Lesson learned(5) Layered recommendations(6) Conclusions

PBL Presentation* 20 minutes presentation + 10 minutes Q&A Session

19 Oct 2009 (Mon)(12 – 2.00 pm)(Bilik Seminar) – Group A1, B1, A2, B2

20 Oct 2009 (Tue)(9.00 – 11.00 am)(DKD4) – Group A3, B3, A4, B4

20 Oct 2009 (Tue)(11.00 am – 12.00 pm)(BKD3) – Group A5

21 Oct 2009 (Wed)(2.00 – 4.00 pm) (Bilik Seminar) – Group A6, B6, A7, B7