WRONG OBJECT OR MATERIAL

A characteristic form of error is performance of the correct action but on the wrong object. This is almost always restricted to cases where there are several items of the same type.

The primary cause of this kind of error lies in labelling or communication:

• No labelling

• Poor labelling with deterioration of labels, either falling off or fading

• Mislabelling

• Poor identification in instructions

• Error in identification of equipment in instructions

The problem is enhanced if objects such as pumps, distillation columns, etc., are not arranged in a logical fashion, with pumps A, C and B in a row, for example. Illogical layout is especially a problem for plants which have been extended, adding new units, new vessels or new pumps in the space available, leaving equipment out of order.

Operations on the wrong object can also be caused by errors in communication, particularly errors in written orders. Leading to error are not only writing the wrong name but also instructions which are not sufficiently explicit, e.g. ‘start the cooling pump’, rather than ‘start pump 101-P-117A’.

CASE HISTORY 6.5 Wrong Ingredient [1]

One of the worst chemical accidents in history occurred as a result of a company running short of properly labelled sacks. The flame retardant polybrominated biphenyl (PBB) was packed into unlabelled brown paper sacks. The substance in powder form resembles magnesium oxide, which was also supplied as a feed additive for cattle. The elements of the accident were therefore readied and required only a mix-up in storage to trigger the accident. The PBB was supplied as additive to feed suppliers, who then supplied the feed to farmers.

PBB does not have an acute toxic effect on cattle in the amounts which were added to the feed. The effects are chronic. The poisoning was recognised as an

54 Human Error in Process Plant Design and Operations epidemic some 6 months after the original distribution of the contaminated feed.

Cattle began to fall, to crawl on their knees and to die. At first, the cause of the

‘disease’ could not be identified. A chemist from a Michigan public health labo-ratory tried to determine possible contamination of feed by using liquid chroma-tography (note that at this time it was not even known whether poisoning was the cause). An unknown substance peak was seen in the chromatograph output. The chemist had coincidentally analysed residues a few months earlier and so was able to identify the substance.

Altogether about 30,000 cattle and 1.5 million chickens were poisoned, and an unknown number of persons ate contaminated meat and drank contaminated milk, with human doses of up to 10 grams.

Labelling problems or lack of knowledge or a combination of both can lead to errors in use of the wrong substance.

A problem with fine chemicals or speciality chemicals is that a given chemical can have many different names. These can include variations in the formal chemi-cal name and differences in trade names. To complicate matters further, production companies often abbreviate the names of the chemicals by using acronyms. IPA can, for example, stand for isopropylamine, isopropionic acid or India Pale Ale!

Even when chemicals are properly labelled, mistakes can be made by operation assistants or plant labourers with limited chemical knowledge. It was once asked, for example, if there was a difference between potassium chlorate and potassium chlo-ride. Given the variations in trade names and lack of an education in chemistry, this is not an unreasonable question. It may surprise some engineers and plant managers, but in some companies, raw materials are in some cases recognised by packaging type and colour, something which is almost guaranteed to cause problems at some stage, when packaging changes or when the wrong product is delivered. A good procedure for receiving materials is needed, with a purchasing and a warehouse manager with at least a degree of training, for any chemical plant. Also, all personnel handling chemicals should be taught labelling practices and substance recognition, as well as the hazards of spills and safe cleanup techniques.

CASE HISTORY 6.6 Wrong Equipment Material [2]

Chlorine was unloaded from railcars by using alloy-reinforced 1-inch hoses.

Because chlorine corrodes most steels, including 316 L stainless steel, the rein-forcement required is Hastelloy, an alloy of nickel.

In the actual event, hoses reinforced with stainless steel were supplied. The first one used corroded within a few tens of minutes. There was no emergency shutdown valve fitted at the railcar end of the hose, and the excess flow valves fitted were, as is normally the case, not sufficiently sensitive to close in the case of a hose rupture. (Railcar excess flow valves are usually designed to close in the case of valve damage in a rail crash.) As a result, in all 22 tonnes of chlorine were released.

Operator Error in the Field 55

CASE HISTORY 6.7 Wrong Hose Connection

A frequent location for errors of object choice is in tank truck unloading onto storage tanks. When fluids are pumped into the wrong tanks, a reaction can occur immediately or later when the liquid is used. Examples which are known in accident records are the following:

• Nitric acid (used for piping sterilisation in biochemical production and brewing) pumped into formaldehyde (also used for sterilisation), caus-ing an explosion

• Hydrochloric acid pumped into sodium hypochlorite and vice versa, causing a release of chlorine and in some cases tank rupture

• Low–flash point solvent or gasoline pumped into fuel oil tanks, with a potential for explosion in the tank or at boiler where the fuel oil is used

The logically best solution to this problem, of using different size hose connec-tors for different substances, has proven to be impossible to organise except in a few isolated cases where deliveries are routine. Even with this solution, accidents have happened in which truck drivers have fitted adaptors to hoses to allow connection to the wrong-size receiving nozzle.

Contributing to this kind of accident have been poor labelling of tanker unloading nozzles, lack of an operator to supervise unloading and lack of written instruction for truck drivers. Well-designed unloading stations have locks on unloading nozzles, so that it is impossible for a truck driver to unload without supervision.

Case History 6.8 records an incident in which a field operator shut down one of two pumps.

CASE HISTORY 6.8 Wrong Pump

A power station boiler had two high-pressure feed water pumps. In order to avoid the need for high-pressure seals, the pumps were provided with pressurised motors. The windings, although enclosed, were subject to the high pressure of the boiler feed water.

It is one thing to pressurise a pump, and another thing to overheat it. To avoid the effects of very hot water on the motor, the design required high-pressure cooling water to be supplied between the pump and the motor.

An operator was told to shut off the flow from a seal water drain line on one of the pumps (Figure 6.1). He went to the pump, and shut off the cooling water flow.

With the pressurisation gone, hot boiler feed water passed backwards through the pump seal to the motor and destroyed it. The result was a shutdown and a loss of several million dollars for the new motor and for the loss in production.

The operator had drained from the wrong pump, the one that was not shut down.

When the pump arrangement was looked at, the reason for the mistake was not too difficult to see. There were 25 pipes and hoses intertwined and arranged

56 Human Error in Process Plant Design and Operations

according to the dictates of efficient flow, not operating logic. The first impres-sion was one of steel spaghetti. The valves, though, were properly labelled.

Labels were moderately difficult to read, not being placed at eye level. Lighting was neither good nor bad; it used electrical lights in a pipe tunnel.

The opportunities for mistake were obvious—several valves were side by side, allowing confusion. The operator had performed similar tasks earlier. Possible direct causes are misremembering of location and confusion of the actual iden-tity of the valve. Contributing factors could be reading difficulties. After the event, the operator had difficulty explaining the exact cause.

A normal risk assessment would identify the opportunity for opening the wrong valve and identify poor labelling, inadequate lighting, proximity of similar but unla-belled valves, etc., as performance-influencing factors. The action error–analysis method in Chapter 19 would identify proximity, misremembering, confusion, lack of knowledge, label misreading and overlooking the label as direct causes and poor lighting as a performance-influencing factor.

There is one hidden contributing cause to this accident. That is, the operator almost certainly did not realise the possibility of a critical mistake and the degree of consequences. As a result, he almost certainly did not apply the degree of care in cross-checking, which should have been required.

In order to provide the operator with the proper background, today the following would be regarded as good practice:

1. There was a proper hazard analysis which identified the problem of loss of cooling.

2. The hazard was identified in the operation procedures as a warning.

3. The hazard-analysis results were incorporated into operator training.

FIGURE 6.1 Two canned high-pressure pumps. Cooling water to the wrong one was shut off, resulting in pump destruction.

Operator Error in the Field 57

In other similar situations, operators have been afraid to ask for confirmation or support when unsure or confused, because they did not wish to reveal their lack of experience. The social climate in a work team can affect error rates significantly.

Unwillingness to seek advice or confirmation can stem from teasing or mild forms of bullying; feelings of inadequacy on the part of the operator and tension arising from the employment situation, especially when downsizing is being considered.

Establishment of awareness and a good team spirit of mutual support are ques-tions of leadership and people management. They can be taken into account in audit-ing and can even be factored into risk assessment, as shown in the next section.