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No. 149

CONTRACTORS

This Newsletter describes some accidents which occurred because contractors did something they should not have done or did not do what they should have done. The general messages are:

Tell contractors in detail what they can and cannot do.

Explain the reasons for our rules; many contractors do not understand the hazards.

Keep an eye on contractors; don’t turn a blind eye.

Also in this isue: 149/8 Gradual change went unnoticed

149/9 Testing smoke detectors

An Engineer’s Casebook — A new generation of plant trip systems

Opening vessels which have been under pressure.

IMPERIAL CHEMICAL INDUSTRIES LIMITED

PETROCHEMICALS AND PLASTICS DIVISION

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149/1 CONTRACTORS BROKE A LIVE LINE

An incident in the Company has shown once again the need for close supervision of contractors who are working in or near operating plants.

A demolition contractor who was removing old pipework attempted to remove a redundant line with a powered shovel. The line broke next to a tank and over 300 tonnes of oil were spilt.

— The pipeline should have been disconnected by a plant fitter before the contractors started work.

— The methods to be used by the contractor should have been agreed in writing.

149/2 ANOTHER ACCIDENT INVOLVING VESSEL ENTRY

The following report was not issued by a back-street manufacturer but by a major European Company which normally has high standards of safety. it shows how, without constant vigilance, standards can lapse and people can start taking short cuts.

The engineer of a maintenance contractor firm entered the combustion chamber of an inert gas plant. He wore a safety harness and was being watched by two helpers, both company employees. He had not waited for the respirator which was to be provided for him. When he was climbing out of the combustion chamber, he lost consciousness halfway up and his body was caught between the ladder and the wall of the chamber. His helpers could not pull him out by means of the lifeline. One of them climbed down — without safety harness — to free the unconscious man, but he too was overcome and lost consciousness. Other helpers finally succeeded in pulling out the engineer, but the helper who was not wearing a safety harness could only be rescued by the fire brigade. He did not regain consciousness; the engineer recovered.

149/3 A LEAK DUE TO A WOODEN FLANGE

A new tank, in another Company, was installed with an unused branch blanked off. A month later the branch was leaking.

It was then found that the tank had arrived with the branch protected by a wooden flange. The wood was painted the same colour as the tank and nobody noticed it.

Always inspect new equipment thoroughly.

149/4 A FLAME TRAP ON A SCAFFOLD POLE

When some oil-soaked pebbles were dug out and replaced by concrete a scaffold pole was concreted into position. When the scaffolding was dismantled this pole was left. A few years later, after the staff had changed, somebody asked what the pole was for and was told that It was a vent on a drain.

It was then fitted with a flame trapl

For other examples of knowledge lost with the passage of time see Newsletters 72/6, 93 and 133/2.

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149/5 A SAG IN A NEW PIPE

A new 4 inch stainless steel pipeline sagged over a length of 14 m and developed a crease. It did not leak.

When the pipeline was installed the contractors found that it did not have the required slope. They therefore cut some of the hangers and welded them together again. One of these welds failed. Other hanger failures were due to incorrect assembly and absence of lubrication.

149/6 OTHER INCIDENTS INVOLVING CONTRACTORS

The following Newsletters described other incidents involving contractors:

125/2 A contractor’s supervisor entered a tank to estimate the cost of cleaning it. Entry had not been authorised. He had a copy of the works rules but had not read them.

106/3 A contractor used a gauge calibrated in bars to test a pipeline which should have been tested at 200 psig. The pipe burst.

105/2 A design contractor designed a bellows for normal operation but not for conditions that occur during shutting down.

104/1 A contractor fitted a lagging support to a new tank; it formed a water trap and the wall of the tank cracked.

102/4 Two contractor’s men repaired a lift without permission and without immobilising it. One of them fell down the shaft.

95/6 A pipeline contractor (in the US) installed a gas pipe through a sewer. Another contractor, called to clear the sewer, broke the gas pipe. Result: Explosion and two deaths.

89/3 A contractor started to acid wash some pipelines without waiting for a clearance. Result:

Explosion.

78/10 & A contractor cut an electric cable while levelling the ground. 11/6

57/6 A contractor used welding gas to inflate tyres.

56/4 & On three occasions contractors connected new equipment to live process lines without 44/1 authority. Result: Explosions.

52/6 Contractors left some rubbish inside the skirt of a distillation column. When a flange leaked, the rubbish caught fire.

45/2 A contractor filled a new tank for pressure test with water using a line that contained some petrol. Result: Explosion. The contractor had strengthened the roof-to-wall weld so the tank failed at the bottom!

149/7 AN EARLY VIEW OF CONTRACTORS

Last year we celebrated the 150th anniversary of the Rainhill Trials. They were held to decide whether locomotive engines or fixed engines should be used on the Liverpool and Manchester railway.

Everyone knows that the trials were won by George & Robert Stephenson’s Rocket. Timothy Hackworth’s Sans Pareil was hindered by a cracked cylinder. The cylinders had been cast for him by Robert Stephenson.

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Timothy Hackworth went back to Shildon a disappointed man, but he had little cause to regret his appearance at Rainhi/. The success of the venture ensured the future of the steam locomotive, and he was to win a major share in that future. One lesson he had learned from hard experience — outside contractors are not always reliable. It was not long before he had his own engine works from which he would send out fine locomotives to many parts of the world.

Anthony Burton, “The Rainhill Story”, BBC Publications, 1980, p 145.

149/8 GRADUAL CHANGE GOES UNNOTICED

Report No. A 129,3 11/A, available (within ICI only) from Division Report Centres, describes two failures of 250 psig steam mains by water hammer. Condensate collected in the mains, in one case because a section of pipebridge had settled and in the other case because a steam trap was isolated by an inaccessible valve.

Over the years steam consumption had gradually fallen and flows through the mains, normally operated in parallel, became too low to prevent blockage by condensate. Because the change was gradual it took place without any critical re-examination of the design.

These Newsletters have frequently stressed the need for thorough examination of modifications to operating conditions. “Creeping” modifications need to be examined as well as step changes. The problem is to recognise when a creeping modification has occurred. Any ideas?

“There is nothing easier than to point out the absence from history books of major phenomena that were imperceptible due to the slowness of their evolution. They escape the historian’s notice because no document expressly mentions them?”

Paul Valery, “Reflections on the World Today”, 1948, p 16.

Other failures caused by water-hammer were described in Newsletters 143/5, 130/1, 57/1 and 4 8/2.

149/9 TESTING SMOKE DETECTORS

I have frequently pointed out that all protective equipment must be tested regularly, thoroughly and realistically or it may not work when required.

lonisation smoke detectors are usually tested by altering the voltage supplied to the detector head circuit and seeing if this sounds the alarm. It does not follow that the detector will respond to smoke.

Martindale are now producing a test instrument which produces a suitable ‘smoke’ for testing detectors. Details from D A G Brown at Welwyn (Extn. 3210).

If you have a domestic smoke detector (see Newsletter 127/10) test it with real smoke, not just by pressing the test button.

149/10 OTHER MEN’S VIEWS No25

Behind every engineering mistake there must lie a human engineer who makes it, either alone or through lack of team cohesion. From a reading of many failure reports it is clear that a happy, close-knit team is a strong safeguard against both design error and failure during construction. There can be no in fallible method of building such a team. It starts with a good engineer/client relationship, and it involves a formally defined sharing of responsibilities which are we/I understood and accepted by all concerned, backed by personal warmth and mutual helpfulness. A change in the team during the course of the work is a step fraught with danger, to be taken only for the strongest reasons, and to be followed by a thorough and time-consuming review of the work p/an and the team relationships.

D W Smith, “Bridge Failures”, Proc Institution Civil Engineers, Part 1, August 1976, p 367.

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149/11 UNUSUAL ACCIDENTS No 109

The Northbound lane of the Milan-Venice highway was closed for several hours after dozens of cars were glued to the asphalt by highly adhesive chemicals which leaked from a lorry following an accident.

The Guardian, 23 December 1980

149/12 DANGER — WASPS!

In a paper on oxidation plant explosions (Loss Prevention, Vol 12, 1979, p 96) I described an explosion in an ethylene oxide plant in Texas which occurred because an air vent line was blocked by the nest of a mud dauber wasp. It seems incredible that a wasp’s nest could block a 1 inch air line but the incident occurred in Texas where the wasps are no doubt bigger than elsewhere!

The real cause of the explosion was, of course, the failure to test the trip system, of which the vent forms a part, regularly.

A report from the US National Transportation Safety Board (NoAAR-81-5) shows that the wasps are still active, in Florida this time.

The take-off of a DC-3 (built in 1942 and still flying!) was aborted because the air-speed indicator was not working. The air intake was found to be blocked with wasps’ nests. The aircraft had not flown for 5 weeks.

The nests were removed (with a coat hanger and screwdriver) and the flight took off. It crashed into the sea and was never recovered; it is not known whether the crash was connected in any way with the faulty air-speed indicator, but the report criticises the airline for a “lackadaisical attitude towards items vital for safe flight”.

149/13 RECENT PUBLICATIONS

(a) “Fire Protection Manual for Hydrocarbon Processing Plants” Volume 2, edited by C H Vervalin and published by Gulf Publishing Co, contains 81 articles from Hydrocarbon Processing, 11 by ICI staff. It covers much more than fire protection. There are sections on case histories, risk evaluation, and safety in operations as well as fire-fighting and fire-prevention.

Being a collection of articles rather than a textbook, it does not cover its subject completely and most of the articles are aimed at the practical man rather than the student who wants to understand the theory. (For comprehensive coverage and theory Frank Lees’ “Loss Prevention”

—see Newsletter 134/10— is essential). Nevertheless Vervalin’s new book contains many articles that you may wish to read or refer to, it saves much time looking through back issues of Hydrocarbon Processing and is well-worth having.

(b) “Health and Safety — Manufacturing and Service Industries” (HMSO, 1981, £4.50) contains items on exothermic reactions (p 16 & 60), permits-to-work (p 62), tanker accidents (p 10 & 11), oxygen enrichment (p 14), tank demolition (p 13), an explosion in a solvent evaporating oven (p 3) and sight-glass failures — in the drinks industry! (p 69). Here are a few extracts:

A mixing machine was started while a man was inside, cleaning it. There was no permit-to-work system. The manager was fined £500 and the company £750 (p 18).

“…. they found themselves in difficulty with the adjustment of some scrapers on heavy rollers. The firm’s solution was to issue a permit-to-work but it was in fact a permit to live dangerously rather than a permit to work in safety. It permitted the fitter to work on the moving machinery with

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the guards removed. A second permit was issued to the first-aid man to enable him to stand close to the jaws of death ready to extricate, or die in the attempt to extricate, the poor fitter after he was dragged into the machinery. In fact, there was a simple solution. It was quite possible to extend the adjustment controls outside the guard so that the machinery could be adjusted, while still in motion, from a place of safety” (p 62).

A cloud of nitrous fumes drifted over a housing estate. The public were advised to stay inside and shut windows. Within a hour every home received a letter of apology and explanation. Press reports, previously critical, showed understanding (p 10).

(c) Report No PC.200,941/A (available from Division Reports Centres) summarises all the fires and explosions, toxic releases and transport accidents in the oil and chemical industries reported in the press during 1980.

An error has come to light in our Loss Prevention Guide No 5, Non-pressure Storage Tanks, issued in 1971.

Section 5.2.6. states that “the emergency vent should be designed to lift at the maximum safe pressure which is 2 ins wg above the design pressure” This is incorrect. The emergency vent should lift at or below the design pressure and its set pressure should be determined by the design authority.

For more information on any item in this newsletter please ‘phone P.2845 or write to us at Wilton. If you do not see this Newsletter regularly and would like your own copy, please ask us to add your name to the circulation list.

July 1981

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An Engineer’s Casebook No 49

A NEW GENERATION OF PLANT TRIP SYSTEMS

Following a review of the safety shutdown requirements of the next generation of plants and of trip systems commercially available at the time, development was started at Billingham in 1978 on an in-house system. This was to embody 1980’s technology where appropriate and be suitable for progressive development over the next decade, particularly in the areas of data gathering and display. Development has now reached the stage that after a laboratory prototype the first operational unit is being installed on a small plant. The decision has been taken to use the system on the Agricultural Division Methanol Project.

The system is all solid state using only a few discrete components in the trip channels but with facility for monitoring these using microprocessor-based data handling techniques. Trip logic is achieved with diodes which are soldered on to a blank matrix card as required.

The main features of the system are:-

1 High reliability trip channels, well buffered from all display circuits.

2 Simple programming of trip logic by diode matrix, changed on line if necessary.

3 In-built facility for on line testing of “close to trip” process valves.

4 Indication of earth faults on individual input and output circuits.

5 Indication of incipient high resistance contact development on inputs.

6 Single output drivers, short circuit protected, for each solenoid valve or contactor.

7 Two-out-of-three or alternative voting of inputs where required.

8 Operation over the range 40 to 57 volts dc from simple rectifier or battery backed up supply avoiding complex regulating circuits.

9 Scanning of channel status and health by microprocessor (512 points per millisecond).

10 Read out of scans by computer to give a print out of events capable of enhancement by software.

Display of the status of trips and defeats can be in almost any form. A small fixed mimic with lights and switches on the plant control console will be used for Methanol. Computer based data displays can be as elaborate as software budgets will allow. In simplest form trip events can be displayed in chronological order as a high resolution event recorder or enhanced in plain English, but developments could yield historical logs and status reports, prompt aids for trip test procedures, display of trip settings and logic, error messages to display which events have not occurred which should have done in a trip sequence and so on.

It is expected that the trip hardware will be standard for major plant with software development extending into the future as needs arise.

Full details of the system are available from Nigel Perry, Control Development Group, Billingham, Ext

B2232.

H M Frankton

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OPENING VESSELS WHICH HAVE BEEN UNDER PRESSURE

Every day many items of equipment which have been under pressure are opened up safely for repair. One man prepares the equipment and issues a clearance certificate to another man who opens it up.

Newsletters 144/1 & 93 described accidents — two fatal — which occurred when the same man both prepared the equipment and opened it up. In this situation it is inevitable that sooner or later, by oversight or neglect, he will open up the equipment before the pressure has been blown off.

Vessels fitted with quick-opening covers should therefore be fitted with a device of some sort to prevent this occurring.

The photograph shows the stopper from a vacuum flask. It is hollow and there is an opening in the wall of the threaded section. The stopper has been made this way to reduce heat transfer but it has another advantage. When the stopper is unscrewed a few turns any trapped pressure is immediately apparent. It can be allowed to blow off or the stopper screwed back. The contents of the flask cannot be ejected.