With rental compressors, preparation and training are crucial to safety
Despite the fact that compressed air systems harness and distribute an incredible amount of energy, significant accidents are rare. To achieve the same level of safety with rented portable compressors, a few additional factors need to be taken into consideration.
When a rental compressor is replacing a compressor that is part of a permanent plant air system, the specification of the rental element is fairly straightforward. It is important to find a rental compressor that is close to the same volume and pressure capability as the original – sometimes special pressure-limiting devices will help achieve this.
The task becomes more complicated when the rental equipment is acting as a complete substitute. Rental compressed air equipment, particularly compressors, can often be too large for the job. This over-sizing can become a problem if other components that are normally part of the permanent air system have been omitted from the rental package: for example, when a large compressor is connected directly to the load, without the addition of a properly sized receiver tank and pressure regulator.
Rapid loading and unloading of the compressor and an inconsistent pressure at the load can quickly have safety implications. Whenever compressed air equipment is rented, the individual components need to form a complete system that is well suited for the intended application.
Safety begins before the rental equipment has been delivered. Documents including specification sheets and operator’s manuals should always be part of the pre-rental request. This includes U-1A forms for pressure vessels such as receiver tanks, desiccant dryers and some moisture separators. Documentation showing the maximum working pressure and temperature rating for the compressed air hose should also be included. Material safety data sheets (MSDS) will be available, but with large rental compressors, especially the oil-free units, the chemicals used will rarely make this a concern.
The specification sheets and equipment drawings are especially useful when considering where to place the rental equipment. Air-cooled compressors, which make up the majority of rental fleets, require a significant amount of room for the circulation of ambient cooling air. Additional clearance may be required to allow room for servicing and replacing a failed machine. Sound-pressure readings should be noted if the equipment will be placed near work stations that do not normally require hearing protection. Similarly, if the rental unit is to be diesel-driven, the exhaust stack should be placed well away from a building’s air-intake.
An area often overlooked when asking for documentation is the local service technicians’ training records. If the equipment supplier does not have a number of staff technicians who have been certified to work with the rented equipment, technical support during an emergency may have to be brought in from other locations. Obviously, this delay could cost valuable time, and pressure unqualified personnel into attempting the repairs.
Service records for the rental equipment should also be supplied. Due to the dynamic nature of the world of rental equipment, it is unlikely that the exact documentation will be available until just prior to the delivery date. However, customers can ask well in advance for the written procedures that the supplier will follow during pre-delivery equipment checks. The exact documentation, usually a completed check sheet, should be provided at the time of delivery.
Unless the company supplying the rental equipment has also been contracted to supply an operator, training for plant personnel is a must. Untrained operators are often a contributing factor in compressed air-related accidents. Training options vary, but an on-site demonstration should be considered the absolute minimum requirement. A formal training session for plant personnel should be considered for projects that are more complex and critical.
With all the preparatory work completed, equipment delivery and set-up day should be fairly stress-free and enjoyable. The biggest safety concern during set-up is to ensure a whip-check device is properly installed on all compressed air hoses. In fact, with a properly designed compressed air system, the only real safety concern is the possibility of a compressed air hose separating from its fitting. If this happens without a whip-checking device or an automatic air shut-off valve installed, damage to property and/or injury to personnel is almost guaranteed.
On set-up day you should make sure that all the provided documentation matches the delivered equipment. All pressure vessels should have the familiar ASME stamp and pressure rating tag. Serial numbers and unit numbers should all match the U-1A forms and service documents.
The overall general appearance of the equipment should also be noted. If the compressed air hose is cracked and weather-checked, it may not be suitable for duty. Inspect all pressure relief valves for the appropriate set pressure. Make sure all rotating shafts and cooling fans have the associated guards securely in place. Finally, check to see if the operators can reach all controls without hanging from the side of a trailer, using ladders, or straddling other equipment.
Operational checks vary depending on the equipment selected. The details of these checks should be included in operator training. Whatever the process, the key to performing thorough and effective periodic inspections is to use a checklist. Ask the equipment supplier to provide a checklist or create one from the operator’s manual. A log should be compiled to document temperatures and pressures. Equipment will usually warn of impending trouble if the operator is constantly monitoring, listening for changes in pitch and tone. High-tech diagnostic equipment, such as infrared cameras and vibration meters, is also useful. The key to good operational checks: start early, document readings on a regular cycle, establish a baseline and look for trends.
Shutdown and Demobilization
Planning and correct procedures are just as important during equipment shutdown. The safe demobilization of compressed air equipment should be included in operator training. It is also important to follow a shutdown checklist. Making sure the rented equipment has been completely depressurized and isolated from the plant air system before disconnecting hoses requires planning and care.
It is not uncommon for untrained operators to activate the emergency stop device on the compressor and break out their hammers in an attempt to disconnect pressurized hoses. The outcome of such a hasty approach is unlikely to be a happy one.