Client
Precast concrete manufacturer
Overview
During a recent blast room overhaul project, our engineering team noticed that our customer’s dust collection unit was ejecting dust from the exhaust fan. A volume of dust could be seen around the dust collector – settled on the floor.
On further examination of the unit, we noticed that the LEV testing log attached to the unit had shown that it had been annually tested since 2007, passing every single evaluation. So, what was causing this dust accumulation?
Differential Pressure and False Readings
During an LEV test, the pressure is measured at two points; at the filter's clean, and dirty side. If the differential pressure indicates that air is passing through the filter freely, it is still working as intended, capturing airborne particulate. If the filter Delta-P is higher than the filter cartridges' maximum operating pressure, it indicates that they are likely spent and require changing.
Filter Perforation
Unfortunately for our customer, the filters inside the unit had been perforated, probably through a prolonged period of being operated beyond their useful life. Once perforated, the differential pressure test displays a false reading.
Perforations in the filter medium then developed, which dropped the pressure reading, leading our customer to think everything was working efficiently. A higher than normal pressure reading should give cause to check the filters even if an LEV test is not due. That said, a filter working within its design parameters, for a period far longer than expected, should also be a cause for concern.
In this instance, dust will pass through the filter cartridge, then move through the fan and air outlet. Through its passage, it can potentially damage the mechanical parts of the LEV and pollute the area outside the dust containment.
How To Avoid False Readings Through Regular Checks and Maintenance
What can we learn from this? There are four potential risk areas to check to maintain good LEV health:
- Moving parts may wear, such as fan bearings or filter shakers. Check them regularly.
- Non-moving parts, such as hoods, ductwork, and seals (which can suffer physical, chemical damage, and wear) also need visual checks.
- Consumable parts, such as filters and flexible ducting, require additional checks.
As stated in the HSE guidelines, it is the operator’s responsibility to make daily checks and report faults. Safety officers or workers’ representatives and supervisors must make weekly or monthly checks.
Additionally, managers must identify problems, receive regular reports from the supervisor, and be responsible for maintenance and testing. Works engineers should repair faults, carry out maintenance, and arrange a thorough examination. And of course, if LEV testing is conducted, it must be logged. LEV testing is a relatively straightforward process that can save facility managers time and avoidable costs if undertaken regularly.
