the safe loading pass scheme

Advice from oil company electrical engineers and the Health and Safety Executive is that the isolation of all electrical circuits in a Hazardous Area Zone 1 - such as a loading gantry - should be by double pole switching.

Advice from oil company electrical engineers is that all freestanding electrical equipment in a hazardous area must be certified safe to use in that area. The only exceptions are small items of personal equipment such as watches and hearing aids which are worn on the body: these are permitted as in the event of a fault condition developing, the user will become aware immediately and take remedial action. This would not be the case with stand-alone equipment.

Firstly, although independent research of ignition risks from a sample of mobile phones has shown that they are not likely to be a source of ignition, individual models of phone have not generally been certified safe to use in a hazardous area; there is a difference between being considered 'not likely to be a cause of ignition' and being certified safe to use in a Hazardous Area.

Secondly, research commissioned by the Energy Institute and carried out by independent electrical consultants revealed that under certain specific circumstances associated with the design of particular loading gantries, it was considered possible that radio-frequency induced sparking could occur between the loading gantry structure and the tanker. That is why the Energy Institute's 'IP Code' was developed in 1992 and updated in 2004.

The UK industry was obliged by law to use insulated return wiring until 1992, and then by the HSE's Approved Code of Practice until 1996. Experience of vehicles wired chassis-return generally has shown that the earth points on the chassis can be prone to corrosion, resulting in high resistance and either sparking or overheating; this situation can be aggravated when the original installation is disturbed, including that induced by the addition of equipment and its connection to the manufacturer's original chassis return connection. Preserving the integrity of the electrical system on petroleum road tankers is considered to be essential to avoid sources of ignition both in transport and when loading or discharging.

The requirement for a central conductor originates with the introduction of low-sulphur fuels, when it was discovered that such fuels tend to have a low electrical conductivity which in turn affects the rate at which the static electrical charge generated in them during loading can be safely dissipated. It was determined by fuels research technologists that for intermediate sized compartments (2 000 - 15 000 litres), a central conductor may be needed depending on the shape of the compartment.

The design of the approved central conductor is based on research carried out on what was then the conventional dip tube dimensions and a specifically designed conductor (a cable). Other designs of central conductor may well be suitable, but this has not been proven by research and therefore we are obliged to be specific on the profile and dimensions of central conductor used.

The loading connection between the gantry and tanker is one of the most critical areas of safety during the loading process; each coupling may handle up to 2 400 litres per minute of a petroleum product, and clearly there is the potential for considerable release of product if the mating parts of the coupling are in any way inadequate. Given the intensity of use of most loading gantries there is the potential for wear and / or damage to occur on the coupling components, and for there to be contention as to whether it is the gantry part or the tanker part which is at fault. Furthermore isolated occurrences of the disconnection of couplers in mid flow have been known to occur.

The wear gauge was developed for the industry to identify when the 'nose' of the tanker's loading adaptor ('API') has worn to such an extent that reliable mating with the gantry coupler cannot be guaranteed, and therefore needs replacing. It replaces an arbitrary visual inspection for wear.

There is no legal or technical requirement for security bolts to be fitted to fill covers (often referred to as 'manlids'). Given that they are prone to seizing in their threads which makes access difficult for wet testing overfill prevention sensors, it is recommended that these bolts are removed and discarded unless there is an over-riding operational reason for retaining them, in which case a suitable preventive maintenance procedure should be in place to ensure the bolts are always removable.

Experience has shown that suitable mudwings can be an effective safety precaution for tankers in the event of a tyre fire, acting as a fire screen to protect the tank. A test to replicate a tyre fire was developed as a result of a research project carried out by Warrington Fire Research on behalf of the Energy Institute, and mudwings are tested against it. Members of the Safe Loading Pass Scheme believe that mudwings that comply with the test are a valuable safety feature for tankers.

None - as long as the camera itself and any associated electrical system comply with the general requirements for wiring and they are switched through the battery master switch. Cameras are entirely benign devices and need no particular precautions; they do not need any certification of installation. (In the event that any connection between a trailer and a tractor is by RF power, the provisions of the Cab phone specification would apply).

In the event that a tanker is unable to start on the loading gantry and has insufficient air pressure to release its spring brakes, this connection enables a tow vehicle to release the brakes simply and quickly and remove the tanker so that the loading gantry is available to other tankers waiting to load.

In fact tyres have a resistance of 1 meg ohm (a million ohms, or 10⁶ ohms) which although comparatively high is sufficient for the dissipation of a static electrical charge. The requirement for other metallic equipment to have a resistance of less than 10 ohms is based on a British Standard, BS 5958 'Control of undesirable static electricity' and more recently CLC/TR 50404 'Code of Practice for the avoidance of hazards due to static electricity'. Metal to metal joints will have a resistance of less than 10 ohms unless corrosion or some other unintended insulating mechanism is present. In the event that the resistance is more than 10 ohms it indicates that an undesirable and potentially uncontrolled insulating process is occurring, the ultimate result of which could be total insulation; the 10 ohms rule therefore provides protection from the possibility of this occurrence to ensure 'connections that are reliable, permanent and not subject to deterioration' (CLC/TR 50404 section 11.2.2).

The effective control of static electricity is a key requirement throughout the oil industry. It is inevitable that a static electrical charge will be built up on a tanker during loading, discharge and possibly during transport, and although earth bonding of the tanker to the gantry is provided by the overfill prevention system, it is considered that providing an earth path to ground (via the suspension, axles and tyres) in all circumstances provides a useful safety margin.

Experience over many years has shown that it is routinely possible to obtain electrical continuity of less than 10 ohms across the conventional lubricating film of wheel bearings but a particular new lubricant appears to have insulating properties. A thousand ohms in this situation may be considered acceptable providing it is known that this will not in time degrade to a lower level of conductivity. CLC/TR 50404 'Code of Practice for the avoidance of hazards due to static electricity' states that 'what is most important is that all (static earthing / bonding) connections are reliable, permanent and not subject to deterioration', and this has not yet been proven to be the case for the lubricant used in the latest cartridge bearings.

The operation of the overfill prevention sensors in each tanker compartment are checked by the gantry controller during loading, but experience has shown that sensors are not always installed correctly, are not wired correctly to the tanker's socket connection, and instances have even occurred when inspection has revealed that a sensor has been by-passed. Furthermore, it would be incongruous to issue a Safe loading pass to tanker for it then to fail to provide a permissive signal to the gantry controller on its next load.

The standard times for inspection of tankers for red safe loading passes are:

Tractor Units : 0.5 Hours

Semi-Trailers: 2.0 Hours, or 1.0 Hour plus 10 minutes/compartment, whichever is the greater

Rigid tankers: 2.25 Hours or 1.5 Hours plus 10 minutes/compartment, whichever is the greater