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Method of clearing bulk cargo hang-ups - Self-unloaders procedure - The Cardox System
Dealing with Cargo Hang-Ups Methods:
Note the following for CSL / Marbulk vessels:
- Hammering on hopper sides.
- Using vibrators.
- Using fresh water hose from the gate-side or hold side, this being subject to written permission being obtained from the consignee, and informing the relevant Management Office and Owners accordingly.
- Air-lances, using compressed air from gate-side or hold-side.
- Complete the checklist for man-entry and carry out the man-entry procedure.
- The cardox system. NB Use of Cardox System is prohibited without prior approval from the management office.
If hang-ups are encountered during discharge and vibrators and hammering have no effect, then the CSL office contingency team must be contacted in order to obtain further expert advice with respect to procedures and to liase with the customers at the discharge port.
For vessels calling at Point Tupper it should be noted that the following preventative measures are to be adopted in order to avoid hang-ups of gypsum during the winter season:
- Hatches not in use are to be kept closed during extreme cold temperatures
- Loading is to be stopped and further advice obtained if large pieces of frozen cargo are seen to be loaded
- The fresh water availability at discharge port, vessel capacity and onboard equipment to be checked
- If possible an agreement to be reached with the discharge port customer to use fresh water as an emergency measure to deal with hang-ups.
IMPORTANT: When discharging GP Gypsum, permission to use fresh water is to be obtained from the Plant Manager and his presence onboard is MANDATORY when using water.
- Hold plastic sheeting is a vital factor and therefore is to be properly maintained with any damaged sheets replaced and allowance made for a sufficient stock along with tools to be carried onboard.
- For all load ports, vessels loading wet gypsum are to give advance notice to the Boston office that possible cargo hang-ups at discharge port could be expected. In such cases the cargo and weather conditions are to be included in the Statement of Facts
The Cardox System:
The Cardox system is a potentially lethal method of clearing hang-ups and is only to be used with office approval and after a full risk assessment has been made. The cardox system was developed in the United Kingdom during the 1920s for use in coal mines where there was a high methane content in the coal. It uses the rapid expansion of carbon dioxide gas as an explosive force to break up large masses of material. The system consists of steel shells which are rechargeable. The shell consists of three sections:
- Activating head.
- Main CO2 Chamber.
- Discharge Cap.
The main CO2 chamber has a heater or detonator fitted at the upper end which has to be replaced after an explosion. The heater is connected electrically via the activating head. It is very important that the electrical connection of the heater is checked for continuity before the shell is charged, as the shell will not explode if the circuit is incomplete.
Between the lower end of the main chamber and the discharge, a bursting disc cap is fitted, which has to be replaced after each explosion. The shell has to be fully assembled, weighed and the weight recorded and then placed into the charging stand where it is connected to a charging pump. The charging pump is in turn connected to a CO2 bottle. The charging pump has a pumping ratio of 60 to 1, (which means that very high pressures are involved inside the Cardox shell). The charging valves can then be opened and charging can commence. Charging is complete when the charging pump stalls (usually after 2 to 5 minutes). If the charging pump does not stall the CO2 bottle is becoming depleted and should be changed for a fresh bottle.
The charging valves are closed and the shell weighed again. The weight of the shell should have increased by 1.25 KG (full charge) although 1.10 KG is acceptable. Any less than this will result in a failed charge. The shell is then ready for use.
When using the cardox system it will be necessary for all cargo hold man entry precautions to be carried out. The cardox shell is most effective when a hole is drilled into the base of the hang-up. The hole must be deep enough so that the charge is buried with only the activating head visible. A length of heaving line is to be tied to the eye bolt in the activating head as the Cardox shell drives itself forward into the pile when it explodes. The heaving line will make retrieval of the shell much easier after the explosion. The two electrical conductor wires are then connected to the length of blasting wire and the man entry team retreats to a safe distance.
The team must either leave the cargo hold together or take cover in an empty door away from the hang-up. The electrical detonator is then, and only then, connected to the open end of the blasting wire. When it has been ascertained that everyone is aware that the Cardox is set to explode, and has taken cover, the detonate button may be pressed.
The Cardox shell will emit a powerful explosive force, which is capable of shifting up to two tonnes of material. Several Cardox shells can be connected together in parallel, and detonated simultaneously to create a larger effect on the hang-up. All spent Cardox shells must be retrieved from the hold so that they cannot pass though the gate onto the belt system.
Precautions Against Hang-Ups:
- Ensure UHMW lining is in place.
- Vibrators are operational.
- Close the hold immediately on completion of loading.
- During discharge, it is important to avoid breaks in the flow of cargo through the gate. When the cargo at a gate shows signs of finishing, then the adjacent gate should start to be opened, avoiding any overloading of the belt, by maintaining a relatively small flow.
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