Rooftop Restoration and the Logistics of Dry Ice
When dry ice blasting is applied properly on the right application, it’s almost miraculous how well it works. Soils, staining and years of detritus strip away instantly and seemingly disappear in the chaos and fog of dry ice blasting. When the fog clears and the dust settles, literally, it’s clear that we’re on the right track to proper restoration. Isn’t it just great when a plan comes together? In the case of dry ice blasting, this is more true than with any other type of blasting media. The challenges associated with dry ice, or solid carbon dioxide, are huge, but so are the profits - when properly executed and applied.
The most recent application that springs to mind came about when I was contacted by Rainbow International of East Central Illinois in Urbana, IL. Project Manager Aaron Gallagher explained that one of his newest commercial customers - one of the largest manufacturers in the state - had contacted him with an unusual cleaning application. Birds (pigeons mainly) had moved in and were starting to cause some nasty problems, both real and perceived. These pigeons had chosen the rooftop of the manufacturer’s R&D building as their new home. (See Image 1)
In particular, the pigeons seemed to prefer the rooftop cabinetry used to enclose the steam apparatus for the building’s heating and ventilation systems. While there is no actual “air exchange” in these outdoor cabinets, the birds do create several unique problems. Maintenance personnel would routinely access these partially enclosed cabinets, disturbing the roosting interlopers with a resulting chaotic rooftop experience. In addition to the whirlwind of upset pigeons, they also encountered nests, hatchlings, feathers, excrement and potentially all the nasty bacteria, viruses and disease associated with this roosting activity. (See Image 2) Anyone that’s ever swung open the door to a chicken coop with the intention of entering will certainly understand what’s confronting these employees routinely.
As with all dry ice applications, a thorough understanding of the unique challenges posed by solid carbon dioxide is important to success on the job site. One of the first and most important rules to successful dry ice blasting is to understand and respect the extremely perishable nature of dry ice pellets. Pellets of high-density carbon dioxide (3 mm in diameter) are the most commonly used form of media. They are produced on an as-needed basis for each customer’s individual order, and delivered to the customer in large, returnable containers (See Image 3). This material will have, on average, a useable lifespan of about five days (depending on density) from the time it’s extruded at the production plant. Dry ice doesn’t melt, it “sublimates.” In other words, it changes from a solid directly to a gas at room temperature. What this really means, in a nutshell, is that dry ice starts to sublimate, or “disappear” into the atmosphere almost immediately after it is produced. If you’ve never noticed this loss due to sublimation, just open a container of dry ice one day after it’s delivered and check out the empty space inside the tote, particularly around the walls and lid. (See Image 4) In fact, generally the solid CO2 will weigh about 9% less after just 24 hours, and another 9% less each day on average, losing density (through sublimation) and picking up moisture (from the humidity in the air.) Each of these effects on the ice is dramatic – the loss of pellet density, or mass, reduces the impact energy of each strike, while the increase in moisture (as frozen humidity) results in “clumping” and reduced “flow-ability” through the blast equipment (freeze-ups, downtime, etc…). (See Images 5 and 6) Proper planning and prompt execution based on an understanding of the logistics of your dry ice, with an eye towards freshness, is critical.
On the rooftop it was determined that several steps were required for the restoration and future protection of the cabinetry. Removal (and eventual replacement) of all soft insulation materials, including all loose debris, would be followed by a thorough blasting of all of the surfaces with dry ice. PPE and other precautions were established as part of the basic protocol. Bird and critter resistant fencing would be installed on all openings to the cabinetry to prevent re-infestation. The restoration and blasting would take place over a five- to seven-day period to begin as soon as possible. Everything was moving in the right direction, until concern about the possible negative publicity the job might stir up surfaced. When men in white contamination suits and respirator masks start swarming over a building, people ask questions. This public relations concern, combined with the fact that the R&D building is located directly adjacent to the building that houses the local newspaper, led to a new rule that the job would only be allowed to proceed during weekend hours to avoid unnecessary attention. This changed the rhythm of this job from one smooth, single event into a series of consecutive weekends of work. Not only did this change the scheduling, it directly impacted the planning, logistics and application of dry ice.
Each dry ice blasting session requires at least one dry ice delivery – this is a given. Each delivery has a cost, therefore minimize deliveries. This does not mean to order less ice than what is necessary as getting more dry ice when you’ve run out is never instantaneous. Remember that this material is made to order with a lead time of 24 to 48 hours, on average. Stopping in the middle of a job to wait on an ice delivery can be a major drain on any potential profit.
Logistically, any time a job takes place on a rooftop, it becomes more challenging. One of the more challenging aspects of blasting with dry ice is getting the material where you need it. Many prefer to have dry ice containers delivered to the job site where it will be used. This preference stems from the desire to have just one delivery, rather than a delivery to the shop or warehouse, then another ride to the job site, as each move requires handling, loading, moving and un-loading. Even though it’s preferable, often the act of delivering to the job site is not possible, due to many factors. One important fact is that someone must be there to receive the shipment when the driver arrives. Many times the job site is not manned when a delivery occurs. In the case of the rooftop job, deliveries would need to take place on a Friday just before the weekend. Care must also be taken when handling the containers. Forklifts, trucks with lift gates and the use of ramps must be considered and carefully employed. Always use your best judgment when it comes to getting dry ice into the right position for use. Luckily, empty totes are much lighter and pose less difficulty in returning them to the plant where they originated (See Image 7). Just don’t forget this last step – you won’t appreciate the invoice for the “missing” tote.
Our rooftop venture would proceed with deliveries made to the warehouse on consecutive Fridays. The containers of dry ice were shuttled to the job site early on Saturday mornings. A lift gate truck would make short and safe work of unloading at the site. Up top, a rented ice blasting machine was staged, awaiting the arrival of that first super-cold batch of carbon dioxide. The last leg of the voyage for the dry ice would require loading 75 pounds at a time into a rotating pair of marine coolers for a quick lift to the rooftop. Once topside, the material was quickly employed to clean to a “white-glove” standard over every interior square inch.
The rooftop restoration presented many challenges, however, the accomplishment of the task, and the many rewards of a job well done, prove that it’s worth every effort.