Lessons learnt from process safety accidents - an article from insurancenewsnet.com

A good article is found on the above title, narrating lessons from five less known accidents. The lessons are,

1. containment of water from fire fighting operations to avoid contamination of water sources in the rundown 
2. to consider all auxiliary equipment also as important as main plant equipment for understanding hazards
3. not to ignore hazards and need for monitoring even during shutdown 
4. positive isolation, purging and checking for hazardous atmospheres (using flame is not a correct check for presence of flammable atmosphere)
5. follow written approval system to override interlocks
6. follow safety permit procedures
7. identify the correct equipment before taking up work
8. communicate with clear identification while handing over the equipment for maintenance
9. ensure physical check by another agency before permitting equipment operation/maintenance
10. hazards from dust, propagation of dust explosions
11. preparation of emergency response management, with detailed instructions for every type of emergency
12. good house keeping
13. establish process safety management procedures
14. inculcate good safety culture, starting from the top management

Dust explosion kills more than 65 persons

In an incident of aluminum dust explosion, likely to have been caused by a flame lit, several persons died, many were injured with more than 80% burns. From the photograph, the roof of the building appears to have been damaged. The explosion sound could be heard at 2 km distance.

Combustible Dusts: The Hazards & How to Control Them

SafetySmart Compliance » Blog Archive Combustible Dusts: The Hazards & How to Control Them

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Dust explosions: little known hazards

Hazards of dust and consequences arising out of dust explosions are still little understood by manufacturing facilities that handle dust of variety of materials, let it be, sugar, plastic, floor (wheat/maize/corn/...), metals (iron, zirconium, thorium,uranium, titanium,...), etc. Otherwise, there would have not been so many incidents every year leading to injuries and deaths of so many.
Proper measures like closed ventilation, maintaining humidity, earthing and bonding, flameproof electrical fittings, static discharge stations, cotton uniforms, periodical cleaning,etc will prevent dust explosions and its consequences.
Proper collection and disposal of dust needs to be given due attention.
An article in the following link is good reading material. There are few reports and video in www.csb.gov on the same subject.
http://www.iwatchnews.org/2012/05/29/8957/unchecked-dust-explosions-kill-injure-hundreds-workers?utm_source=iwatchnews&utm_medium=web&utm_campaign=rss

Blast during cleaning of dryer unit in a bulk drugs company

In an incident at about 0615 hr, a chemist and two helpers received 85% burns during the cleaning of a dryer unit in a pharma firm that makes bulk drugs. A worker of the factory said that such incident never took place in the dryers of the pharma units in the industrial area.
A fire resulting after the explosion spread quickly due to chemicals and solvents in the area. The reason could for the incident could not be ascertained.
As it happened during dryer cleaning, the reason could be the static electricity and dust explosion. As solvents in the area caught fire, it is presumed that the workers might have used some solvent to clean the dryer. It is likely that the static electricity produced during cleaning might have discharged in the form of a spark. The dryer unit might have lot of loose particles in the form of dust and any disturbance during cleaning might have caused the dust airborne and to catch fire from the discharge of static electricity leading to dust explosion. Or, if they used large quanity of solvent inside the dryer, the vapors also might have caught fire leading to explosion in the confined space.
http://www.youtube.com/watch?v=HIqbwSmd_LY
http://articles.economictimes.indiatimes.com/2011-11-28/news/30450554_1_blast-three-persons-facility

A report on explosion in West Pharmaceutical Services can be read here.
http://en.wikipedia.org/wiki/West_Pharmaceutical_Services_explosion

Dust explosions kill workers

Rules lag as factory dust explosions kill workers | ajc.com

The above link is about US Chemical Safety Board investigations on dust explosions and their recommendations. As I posted earlier on the same subject, I am surprised to know that even iron dust catches fire. Many times we concentrate on the dust that we see in the shop floor. But, airborne dust settled at roof level or on the surface above false ceiling or in the elevated surfaces adjacent to the building from which dust is generated require more attention because persons in these areas are unaware or complacent as they are not the dust generators. Any disturbance due to wind or occasional work in the elevated surfaces or sparks generated from electrical fittings at roof level can be a source of dust explosion. It is said that the dust explosions after the primary explosion are more severe. The dust explosion is identified with a roaring and thunder sound and therefore all shop floor persons should be aware of these symptoms and should run away for safety.

Dust explosions are also possible with grain powder and therefore requires communication of dust explosion hazards to these groups also. Enclosures for dust generating equipment, earthing, flameproof electrical fittings, regular cleaning of equipment and ducts that may contain dust, wet mopping, avoiding synthetic dress and static charge dissipation stations are some of the measures that help in preventing dust explosions.

Dust explosion in grain elevator - 3 dead, 3 missing

An apparently dust explosion in a grain elevator in US caused 3 deaths and many unconfirmed injuries. 3 persons are missing. The blast effect could be felt upto 4 miles from the place of the incident. The incident occurred while loading corn into a train.The full story is available here.

Some statements on safety

Following are some of the statements in "Process Safety Analysis - An Introduction"  by Bob Skelton published by Institution of Chemical Engineers, UK.

1. A good safety culture ensures that both the spirit and the letter of the law are fulfilled.
2. Attitude to safety should be highly visible and shared at all levels within the company.
3. A well managed company is almost invariably not only a profitable company but a safe company.
4. Changes in existing plant are costlier than that introduced in design stage.
5. Design should be such that operator intervention is not needed for at least 30 minutes after an incident. Experience has shown that operators can not always be relied upon to make the correct decisions under immediate post-accident conditions.
6. Safety in design must be both proactive and reactive. Changes, once a plant is built, are very expensive compared with changes at the design stage.  It is not sufficient and cost efficient to make safety review after completing the design and then BOLT ON safety devices. It will not be cost effective. Engineered safety is BOLT ON safety. Engineered protective devices can fail and never place too much reliance on BOLT ON safety.
7. Commissioning is one of the most hazardous parts of any process plant operation. Not only do design errors which escaped previous checks manifest themselves but problems due to construction errors also become obvious. In addition commissioning generates hazards of its own as the plant moves from construction to operating status. It is essential that a formal set of checks be carried out before process fluids are introduced for the the first time.
8. Fire and explosions can be prevented  by not exceeding 25% of LEL. Flammable atmospheres can be avoided by ensuring that fuel lines and tanks are pressurized so the flammable material leaks out rather than air leaking in. good ventilation of vessels and plant areas can maintain safe working conditions.
9. Dust explosions are best prevented by good housekeeping - that is, by keeping the concentrations of dust down and perhaps keeping the dust damp. Inerting by dilution with non-combustible dust is another effective technique, frequently used in coal mines.
10. The risk is serious in case of static electricity, if the relative humidity is below about 60%.
11. Explosives manufacturing facilities are usually designed so that the buildings are separated by safe distance, surrounded by earth mounds so that any explosion will go upwards rather than affect other plants in the area. In addition there is usually a limit on the number of people allowed in a building.
12. Fire fighting water causes more damage than the fire itself, when polluted water is let into rivers. There may be a conflict between accepting the atmospheric pollution caused by letting the fire burn out and the water-borne pollution caused by fighting it.
13. Non-process hazards account more than 70% of all accidents in process plant.
14. Many of the worst accidents in the process industries are the result of bad maintenance practice. Ex: Piper Alpha and Flixborough
15. As many people die by asphyxiation as from toxic gases.
16. A good health and safety policy is always cost effective; most organisations grossly under estimate the cost of accidents, often by an order of magnitude. The organisation should be such that the attitude to safety is highly visible and shared at all levels within the company. Active participation is encouraged to promote the objectives of not just preventing accidents and industrial illness but motivating and empowering everyone to work safely.
17. A safety culture, once established, must be maintained, any any tendency to careless practices stamped out at once. Experience shows that 80% of accidents tend to happen to 20% of the workforce - the young and the old being particularly vulnerable.  Many accidents are caused by operators not fully appreciating the significance of small, but nevertheless important changes.
18. A good system of accident reporting is proactive and reactive, whereas most tend to be purely reactive.
19. Effective safety at all stages of a project - from inception to demolition - can only be achieved if there is a commitment at all levels. The senior management must see health and safety as being just as important as profitability and they must make certain that all their workers are aware of this fact.
20. A well managed company is almost invariably not only a profitable company but a safe company.
21. In hazard analysis, a distinction must be made between routine operator action and operator intervention in an emergency.  For routine operator action, the operator can usually take time and is under no great stress. Safety assessments involve the prediction of the likelihood of errors when the operator is taking corrective action against alarms. The time for corrective action may short, the operator is liable to be under some stress and so the probability of errors is greater.
22. Total elimination of human error will never be possible. Use must be made of the science of ergonomics to ensure that everything possible is done to enhance the strengths of human operators whilst at the same time allowing for the weaknesses.
23. The most important rule is, 'inherent safety is better than engineered safety', ' what you have not got can not leak'. Even elaborate safety devices can't reduce risk to zero due to the escape of a noxious substance, but replacing a noxious substance by a more benign one could well eliminate that risk altogether.

 

Dust explosion

There is one more dust explosion at Hoeganaes facility, Tennessee on May 27th in which two persons died and another is seriously injured. Earlier in the explosion on 31st January, two persons died and a person was injured during the flash fire on 29th March. My post on 14th May gives some details of iron dust explosion provided at CSB website. The latest incident appears to be initiated by hydrogen gas leak from 3x7 inch hole on a hydrogen pipe in a trench. The trench also contains nitrogen and water lines. After hearing hissing sound from the trench, nearby annealing furnace operators informed maintenance who unsuccessfully tried to remove the trench cover. Later tried to open with the metal chain hooked to a forklift and during cover opening, a flash and explosion occurred. The statement for news conference on June 3, 2011 by CSB gives status of their investigations and a short video (1:16 min) on iron dust flash fire experiment.
The shortfalls at the plant identified are poor containment of dust, improper dust collection, thick layers of dust, unsuitable electrical fittings and availability of various ignition sources nearby.These types of causes are well reported and NFPA Standard 484 and we fail to take measures to eliminate these types of causes.
Providing dust containment and collection, elimination of ignition sources, flameproof electrical fittings, providing and maintaining obstruction-free aisles, regular wet mopping and incineration of mops at safe distance, testing of electrical continuity between equipment and earth pits, maintaining 50-60% humidity, use of antistatic uniform and PPE are some of the measures that will surely help in avoiding such incidents.

Iron powder catches fire

A CSB investigation finding mentions that iron powder combustion lead to a fatality and injured another. The atomized iron powder dust dislodged during inspection by maintenance workers caught fire. Though, we know dust explosions, like ammonia fires/explosions, iron powder fire also is difficult to digest. Such information should be brought to the notice of all employees so that they will not be lax on their part.

Dust explosions are said to be more dangerous than normal explosions, as initiation of dust explosion can disturb the settled powder making it airborne and lead to secondary and tertiary explosions.
CSB mentions that metal powder dust flash fires and explosions cause more serious injuries than flammable gas or vapor fires because of radiant heat. A CSB study on 281 combustible dust fires and explosions during 1980-2005 indicate 119 deaths and more than 700 injuries due to these incidents.

The best way to avoid dust explosions is to have dust collections systems, regular wet mopping, flameproof electrical fittings, maintaining atleast 50% humidity, static charge discharge mechanisms, etc and maintaining records to ensure that safety systems are maintained.
A news item on the above is also available here(1), here (2) and here(3) , here(4)..