Sterilization

Animal lab sterilization has recently seen a demand for greener technologies that require less maintenance. This puts the pressure on equipment engineers to develop innovative ways to approach sterilization. While traditional steam autoclaves use water more efficiently, dry heat sterilization provides an alternative to steam that uses no water, less energy, and requires less maintenance.

The incumbent technology in today’s bulk sterilization marketplace for animal cages utilizes steam as the heat transfer method to raise the temperature of the product load to the level needed to sterilize the cages. However, bulk sterilizers that use dry heat are gaining ground.

Physics tells us that the heat transfer rate of steam is greater than that of air, which seems to imply that steam is more efficient.Why consider the dry heat alternative?

Compared with steam, dry heat is a greener technology that eliminates water usage, provides more flexibility for installation locations, and costs less to own and operate.

Greener
The newer steam autoclaves in general are designed to be more efficient with water usage but the required amount of water used in a typical cycle is considerable. The water needs to be heated to generate steam for sterilization, and then it must be cooled for disposal. Conversely a dry heat sterilizer uses one utility, electricity.

The dry heat sterilization systems are providing a high degree of thermal efficiency and present very low skin temperatures. This combined with the fact that there is no steam present to infiltrate the work environment when the door is opened, provides for amore comfortable environment.

Cycle Time
Modern dry heat sterilization systems using focused forced air convection technology are consistently decreasing the cycle time. Depending on the load configuration and cool down requirements, the typical cycle lasts 2.5 hours.

The sterilization cycle consists of three segments: heat up, soak, and cool down. During the heat up segment, the oven and its load of cages are raised to the pre-set sterilization temperature of 300°F. The cages soak for a pre-determined time period in order to facilitate complete sterilization, after which a forced cool down segment rapidly brings the oven and product down to a manageable temperature.

Flexible Installation Options
A critical logistical point to consider when installing a bulk sterilizer is the task of getting a large piece of equipment into the building and placed in the desired position. For labs that want to replace their old equipment, navigating bulky equipment through an existing building layout may prove difficult and/or expensive.

Dry heat systems can be designed in a modular fashion where the individual modules can be fitted through most corridors, service elevators, and doors. The modules can be reassembled at the required location of use.

Cost of Ownership
A fundamental factor in deploying any technology is cost, including dry heat sterilization systems. How much will it cost me today, next week, and next year to maintain and operate?

• Initial Cost: The initial cost of available dry heat systems is about 60% of equivalent sized steam autoclaves.
• Rigging: A dry heat sterilizer is two to three times lighter than an equivalent steam system. Because the dry heat sterilizer can be rigged in place as modules, there are a considerably less rigging challenges and costs.
• Installation: The dry heat sterilizer does not need to be pit mounted. Instead, a steel plate floor in the sterilizer allows the load of animal cages to be rolled into the oven from plant grade.
• Operations: A recent study at Rutgers University showed that their 139ft3 bulk dry heat sterilizer loaded with 180 pre-assembled cages plus bedding has a cycle utility cost, (preheat, sterilize, cool down) of $4.71 based on electricity costs of $0.13kw/hr.
• Maintenance: The dry heat systems operate at ambient pressure eliminating many of the maintenance considerations of high pressure steam units. This is not to say that no problems can be expected with a dry heat sterilizer, but the simpler technology means issue can be addressed with more ease and less expense.
• Extended cage life: In life cycle simulations, cages showed zero visible cage defects after simulating six years of usage with weekly dry heat sterilization cycles.