3.0 Testing hoses used in Vacuum tanker operations.
For vacuum tanker operations the driver should perform an electrical continuity test between the end of the hose through which material will be sucked, back to the tank or chassis of the tanker. This test ensures that there is electrical continuity through the hose sections and onto the tanker itself. Any charge created on the metal components of the hose during the transfer operation will travel via the hose onto the tanker and down to earth via the tanker’s Earth-Rite MGV system.
Hose continuity tests are normally performed with a multimeter but given the circumstances in which the vacuum tankers and drivers are operating, which are typically harsh industrial environments and zoned atmospheres, the meters, at minimum, need to be robust, rugged and certified for use in zoned hazardous areas. More importantly, the technical competency and training required to operate the meters may present more problems than they would solve.
An ATEX / IECEx hazardous area certified device like the OhmGuard® Hose Continuity Tester enables drivers to perform a simple and quick PASS or FAIL hose continuity test prior to each transfer operation. The driver simply looks for a pulsing green LED from the OhmGuard Hose Continuity Tester enables drivers to perform a simple and quick PASS or FAIL hose continuity test prior to each transfer operation. The driver simply looks for a pulsing green LED from the OhmGuard clamp to indicate complete continuity through the interconnected hoses and, in turn, the hose’s connection to the tanker. If the OhmGuard does not provide a PASS indication to the driver he can test each individual hose section to isolate the faulty hose and remove it from the transfer operation.
Figure 4. The OhmGuard is a portable device that consists of 2 clamps joined by Cen-Stat cable (blue). The driver simply attaches one clamp to the tanker and the other clamp to the end of the connected hose sections. The pulsing green LED indicates good continuity through the hose and tanker. The tanker should be grounded with a truck mounted earthing system like the Earth-Rite MGV.
4.0 Testing hoses used in the loading or unloading of bulk chemical road tankers.
When chemical road tankers are bottom loading or offloading product through sealed hose connections at bulk storage chemical terminals or chemical manufacturing sites they should be grounded with a gantry mounted or tanker mounted static earthing system. In addition the hoses through which the product is transferred should be conductive.
One of the risks of using a hose with an isolated component in a closed connection transfer, e.g. the metal helix breaks contact with the hose coupling, would be at the end of a transfer operation when a vapour may be present and as the driver removes the hose from the connector could receive a static spark discharge from the wire helix or the wire helix could discharge a spark onto the site’s loading connection point.
Using an OhmGuard the driver can test the conductivity of his hose prior to the transfer operation. This ensures that all the hose sections, including the couplings on both ends of the hose have proper continuity.
If the driver is transferring the contents of the tanker into an Intermediate Bulk Container (IBC) at a customer site, he should check the electrical continuity of the hose prior to transferring the product into the IBC. The tanker should be grounded and the IBC bonded to the tanker, or grounded itself.
5.0 Testing hoses when unloading road tankers at petrol service stations.
For situations where road tankers are gravity offloading or pumping petrol to underground storage tanks at petrol service stations, the road tanker is assumed to be grounded via the transfer hose connection to the service station coupling that feeds into the underground storage tanks. Despite the increased use of plastic tanks and piping the receiving tanks are assumed to be providing the connection to a true earth ground.
Although road tankers are protected from static electricity with dedicated static ground monitoring systems at the refinery or tank storage terminal, no earthing checks are performed at the service station unloading point even though the immediate area where the hose is connected to the service station filling point and to the tanker itself is defined as a Zone 1 atmosphere.
Figure 5: Road tanker loading underground tanks at a petrol service station.
To eliminate the risk of charge accumulation on conductive hoses, after the driver completes the connection of the hose from the tanker to the filling point of the site, he can test the continuity between the tanker and the service station filling point with an OhmGuard which will verify that the hose is conductive and is securely bonding the tanker to the filling point of the service station. The OhmGuard can remain connected during the transfer with the green LED pulsing continuously to indicate a good bond between the tanker and the service station filling point. Provided the filling point at the service station has a verified true earth ground connection, static electricity will not accumulate on the hose or the road tanker. Quoting from section 5.6.2 of CLC/TR: 60079-32-1 (ref. Table 1) which addresses road tanker deliveries:
“Deliveries from road tankers to medium sized tanks are performed via flexible hoses using either gravity feed or pumps on the vehicle. Electrostatic ignition hazards may occur as a result of sparks from insulated conductors (e.g. hose couplings or the road tanker as a whole), brush discharges from non-conductive hoses or brush discharges within the receiving tank.
The following precautions are recommended:
- conductive or semi-conductive hoses (see 5.5.5) should be used;
- ensure that the tanker and all metallic couplings are bonded to the tank being filled. Separate bonding is not needed when the hoses are conductive or semi-conductive as bonding is provided by the hose;
- when connecting the tanker to the receiving tank, first connect the hose to the tanker and then, before removing the tank fill pipe cap or making any other hose connections, equalise the potentials by touching the end coupling of the hose on the fill pipe cap or any other metallic part of the tank;
- providing the maximum safe filling velocities for medium sized tanks are not exceeded (see 5.4.4) there is unlikely to be an ignition hazard within the tank. If the liquid contains a second phase, the filling velocity should be restricted to 1 m/s;
- the continuity of conductive hoses should be checked regularly.”
Hoses play an important role in hazardous area operations and owing to their direct interaction with moving liquids and powders are especially at risk of becoming electrostatically charged. It is important to ensure that hoses used within a hazardous area are capable of transferring electrostatic charges from their structure onto grounded equipment. At no point in its structure should such a hose be permitted to accumulate static electricity. Even so, no hose is immune to operational wear and tear and regular electrical continuity testing will enable detection of damaged hoses. Although periodic testing will identify faulty hoses, a simple test by an OhmGuard hose continuity tester, prior to each transfer operation, will ensure a faulty hose is identified and removed as soon as it becomes an ignition risk.
. Thomas H. Pratt, 2000, “Electrostatic Ignitions of Fires and Explosions”, AIChE/CCPS.
. Britton L.G., 1999 “Avoiding Static Ignition Hazards in Chemical Operations”, AIChE/CCPS.
Mike O’Brien, Managing Director for Newson Gale
If you have any questions relating to the topics discussed in this article,
please contact Newson Gale.