Renewable energy powers medical instrument sterilization

Sterilizing clinical and surgical instruments is tough enough in hospitals with reliable power supplies and environmentally controlled clean spaces. In rural areas of undeveloped countries, that challenge can be exponentially more difficult. Rice University Business Professor Doug Schuler hopes to address that challenge with the Sterile Box, a system packaged into a shipping container that uses a solar array to provide electricity and autoclaving for remote medical instrument sterilization.

“The place where this system will prove out is in a place that is outside the grid, most likely in a developing country, outside of a main city where they have demand for sterilization of medical devices. That’s the immediate goal,” Schuler says.

Sterile Box is a follow-up project to a 2009 effort, sponsored by the Shell Center for Sustainability. In the initial effort, Schuler and his students developed a solar-thermal cooking device that they brought to Haiti. Though it technically worked, it wasn’t user friendly. However, Schuler says the project gave him insight into the severe power challenges faced in remote areas.


Sterile Box

The World Health Organization (WHO) reports that nosocomial (within the health facility) infections of patients and healthcare workers are linked to contaminated equipment and poor infection control practices, conditions that are especially prevalent in developing countries. Though the use of autoclaves for sterilization is not new, they typically use gas burners requiring tanks of propane, butane, kerosene, and other gases.

A 20ft steel shipping container houses Sterile Box’s sterile processing unit. Inside the unit, a foyer separates the sterile processing operations from environmental elements. This area has a small window that allows the sterile processing staff to receive soiled instruments from the outside. Four areas lay further inside the box: decontamination, partitioned from the other areas by a half wall; preparation; sterilization; and drying and storage.

In the decontamination area, staff disinfects devices via a three-basin sink. The first sink is used to remove gross debris from the instruments; the second sink is used to soak instruments in enzymatic detergent followed by scrubbing with nylon brushes; and the third sink is used for final rinse. Water flows to the sink from a system of two tanks joined by tubes: a 55 gallon receiving tank on the ground with a hand-powered diaphragm pump that pumps water to a 50 gallon tank located on the roof. At the sink, the staff controls a ball valve to bring water from the upper tank into the sink through tubing at a maximum flow rate of 22.2L/min.


In the sterilization area, a non-electric, gravity steam sterilizer (WAFCO 1925X), heated by a 750w electric hotplate that the team constructed, sterilizes the instruments. Electricity comes from two 12V batteries joined into a 24V storage unit that is charged by a solar photovoltaic (PV) array (four 230W panels for 920W or 0.92kW) mounted on Sterile Box’s roof. An Outback Power Systems Controller mounted inside the container regulates the flow of electricity.

The container’s usability is enhanced by several additional features. Two windows provide daylight, and work in the dark is possible by three 5W DC light bulbs powered by the solar PV electrical system. Air flow is facilitated by window screens, three floor-level air vents, mesh across the entire outside door opening (approximately 2.5m x 2.5m), and two wind-powered turbine fans through the ceiling. Temperatures inside the box are minimized by radiant barrier insulation and reflective paint on the outer surfaces of the container. Functional outlets (for running small appliances such as a fan and charging cell phones and laptop computers) are supplied by a 600W inverter connected to the electrical system.

Jean Boubour, Katherine Jenson, Hannah Richter, Josiah Yarbrough, Z. Maria Oden, and Schuler co-wrote the paper “A Shipping Container-Based Sterile Processing Unit for Low Resources Settings” explaining this system and how they worked to achieve this project.

“Half-way through the project we were interested in bringing electricity into the box, that’s when we decided to use solar panels,” Schuler explains.

“Now, with an inverter, we have electricity to plug in a laptop and support telemedicine. We’ve also been concerned about the motivation of the staff because if they don’t do their job, it doesn’t work. So we’ve been thinking about how do you set this up so it is a relatively nice place to work? It was another reason to use electricity. Having access to electricity is so important to people because of cell phones. So, having that inverter in the box provides more incentives to work.”


The team assessed the efficacy of sterilization by testing the decontamination and sterilization processes. Between May 27, 2015, and Aug. 17, 2015, the team conducted 61 trials of the sterile processing unit.

Decontamination was successfully achieved in each of the 61 trials. The mean initial contamination level was 709.95 adenosine triphosphate (ATP) units, with a range of 47ATP to 5,324AT units. The post-decontamination level was a mean of 4.49ATP units, with a range of 0ATP to 31ATP units. In every trial, the post-decontamination level was well below 45ATP units, the standard cut-off for contaminated versus clean.

Sterilization also was achieved in each of the 61 trials using four indicators of sterilization efficacy. Recommended exposure temperature and time for sterilization is 121°C (per the sterilizer’s geared steam gauge) for 35 consecutive minutes, which was met in every trial except one, when the experimenter recorded the time as only 25 minutes.

“We replicated what they do in a modern hospital in terms of sterilization and process,” Schuler says

The team’s successes gave them an estimated probability of a failed decontamination and sterilization event of 0%. (Using the Rule of Three, developed to estimate the confidence around an intervention, the team estimates with 95% confidence that the error rate would be less than 0.5%.)

“I’d like to tell you that when we started down this path years ago that I had this perfect plan. Originally, we probably would have used gas, but I think because medical is connected and there is this push for connectivity, we have a function that we can bring to a remote area that the governments of developing countries could never realize,” Schuler says. “It’s hard to move people around in these areas since the roads aren’t very developed and fuel is expensive, so having the ability to have a fairly inexpensive computing device in the box is huge and a very positive thing.”

Schuler says the next step is working to get this into the field.

“The next step is field testing in a few sites to get some feedback from users and the process. We’re in the process of that right now,” Schuler says. “If that goes well, the next step is to figure how to disseminate this thing more widely.”


Arielle Campanalie is the associate editor of TES (Today’s Energy Solutions)