Friday, June 7, 2013

Sustaining a City in a Long-Term Power Outage

A few comments on this fascinating study from Pittsburgh (site of Carnegie Mellon, which is a center of excellence at studying critical infrastructure issues).  The key theme that emerges for me is the interaction of the liquid fuel system (particularly diesel) and the electricity system.  In a short outage, lots of critical infrastructure has diesel generator backup, and so the hospitals, 911-call centers, and so on can continue to operate.  However, they typically have limited fuel storage capacity (if for no other reason than that diesel doesn't keep indefinitely), and so in a long outage, the availability of diesel becomes critical to keeping everything together.

To illustrate the time factors, consider the water situation in Pittsburgh:
The Pittsburgh Water and Sewer Authority is responsible for providing the city of Pittsburgh with clean water for household and business use. Most of the electricity required at the Aspinwall Water Treatment Plant (WTP) is consumed pumping water from the river. From the treatment plant, water is pumped to the three primary reservoirs. About half of the water from the primary reservoirs is delivered directly to homes and businesses. The other half is pumped to a series of smaller reservoirs, tanks, towers, and standpipes around the city. In this report the main reservoirs are referred to as ‘primary storage’ and the smaller storage facilities as ‘secondary storage’.

Pumping into storage facilities is usually activated when water levels in the facility drop below a certain level. Storage facilities are normally kept full, but may drop to 80% in the evenings. Electricity is only needed to pump water into storage facilities. Once water is stored at a high point in a reservoir or a tower it can flow by gravity to any customer located below it.

During the course of this study, we found that immediately following a blackout, water supplies will be unaffected. In the absence of any backup generation, after one day of power outage, as many as 15% of customers could expect to lose water as secondary storage is depleted. All secondary storage is likely to be depleted after three days, leaving 50% of the population without water, increasing the load on primary storage and depleting the first of the primary storage reservoirs within about nine days. The last water storage will be depleted after two weeks.
So a short outage is no big deal, but between the first few days and two weeks, things start to go really bad, until the point where everyone is dependent on emergency measures:
Current emergency plans include distribution of water by tanker trucks (called water buffalos). Emergency response plans at the city and county level include steps to acquire these trucks from local governments and agencies. With a typical capacity of 2,500 gallons, these trucks would only be practical or providing minimal supplies of water. To provide all 370,000 people in Pittsburgh with an emergency one gallon ration of water per day of water would require 15 trucks working 18 hour days. To provide even 10% of normal drinking water supply would require 240 trucks
The water system itself at the time of the study (2004) lacked emergency power backup, but note that the water buffalo trucks require diesel.  The fuel supply in an extended outage would be very uncertain (as we saw during the damage from Sandy also):
Gas stations become more critical to the citizens of Pittsburgh as a blackout endures. Initially, most people can rely on the gas already in the tank. But over time, the demand for gas will grow, as people will want to leave their homes to procure needed items, or to just “get out.”

There is little incentive, however, for gas station operators to install generators. The probability of a long outage is sufficiently low that the owner will likely not recover the cost of a back-up generator over its lifetime. Thus, if gas stations were to be made more survivable, the government would likely have to step in. For example, is it feasible to designate a few fueling stations around Pittsburgh as “emergency” gas stations and provide incentive to install backup generators?
Pittsburgh is a distribution hub for the fuel system, so there is a lot of fuel there, but it cannot be accessed without electric power:
The second component is the distribution within the city to points of need. We are confident that there are enough trucks to supply fuel to all the critical services outlined in this report. However, the pumps that pump fuel from the large storage tanks are vulnerable to electricity outages. We recommend that this issue be studied further to determine if this dependency is acceptable.
So it sounds like a lot of diesel backup generators would be likely rendered useless for lack of fuel before too long.

The theme of critical infrastructure is in private hands with differing incentives also shows up in the context of grocery stores:
Giant Eagle is the dominant player in the Pittsburgh grocery market, with twelve stores within the city limits. Most have generators to power critical equipment such as emergency lights, but they do not have backup capacity for refrigeration equipment. Pittsburgh has relatively reliable power, and Giant Eagle has decided that large backup is not economically attractive or necessary. On the other hand, Giant Eagle stores in the Cleveland area typically have complete backup capacity, since power there is less reliable.
Thus the picture is that for a power outage of days or less, people have gas in their tanks, food in their cupboards, etc.  But for outages beyond that duration, the means to supply the populace with food, fuel, and water is not survivable and will rapidly degrade, and people will quickly be reduced to "refugee" status - needing either to leave to somewhere better equipped, or to rely on emergency measures like water buffalo trucks and food handouts at central distribution points.


dr2chase said...

Off in Portland, there's these guys, proposing to help with cargo bikes:

Unfortunately, the math seems to utterly fail for water delivery. A plausible upper limit for cargo load is 200lbs (I've carried that on several occasions, it is a lesson in physics) or 25 gallons of water -- 1/100 of a truck load. The only advantage the bikes have is fuel flexibility; not only will they run on anything edible (include vegetable oils, sugar, and dilute ethanol), quite a few of us are carrying a substantial "reserve fuel supply" (in my case, I estimate a minimum of 1000 miles; I am 2000 miles over my weight in college).

Of course, all of this assumes that this hypothetical horde of cargo bikes is also helpful and public-spirited and hangs around; at some point, they might decide to just get the heck out of town, which they are well-equipped to do, since bikes are not impeded nearly as much as cars are by downed trees, washed out roads, minor flooding, or landslides.

Stuki said...

As long as "there is a lot of fuel there", 'there' being a fairly dense metropolitan area, it won't just be left laying around while people dehydrate, starve or freeze to death.

I mean, absent a generator preinstalled at a gas station, why would not someone needing gas for his ubiquitous pickup truck put his own generator in the bed and roll on over? Even handpumps could be used in a true emergency, but given the sheer number of generators (and car altenrators+inverters) available in the USA, why even bother?

Once refrigeration of food in a given grocery store starts getting problematic, you'd hope the store owner would have the sense to firesell their stuff while they still could; to people that still had power, or had better backups and more-better fridges. Or perhaps to store owners in unaffected areas.... Things of genuine value are rarely left unused. At least as long as people are not barred from even considering whole rafts of potential ways to make do.

Of course, if the disruption drags on, eventually there will be no "fuel left there." And no food. Then the real hurt is on.

Dean said...

We came very, very close to this when I was living in Montreal during the 98 Ice Storm. 5 out of the 6 main power lines leading onto the city went down and it was only pure luck the sixth didn't as well since it had the same capacity and the same amount of ice build up.

As it was, the power outages were okay for us, but could have been down for three weeks much like the south shore saw.

dimposter said...

We had all these issues and more in a recent earthquake. All utilities and use of the port, airport, tunnels and many bridges and roads was lost across most of the city on the day of the event. Power, telephones, water and sewage were still offline in a significant fraction of the city many weeks later. In some places some services are not able to be fixed, ever.

The report and Stuart are correct that interactions become critical. I'm told the central hospital UPS took over smoothly, but then itself failed a couple of hours later due to shocks stirring up sediment in the diesel tanks. Patients in certain wards had to be carried down many stories by medical staff with torches in their mouths. As the report notes at the end, communications are the most critical. The cell networks were shattered and overloaded, but still somewhat available for emergency service. One major provider almost lost their entire network however when access was denied to refuel their base site UPS. The CBD was badly damaged (over 1000 buildings have now been demolished) and entirely cordoned off by police and army, and the cell provider's base was within the cordon. The problem with access was itself communication, which was patchy between the checkpoint and an under-siege civil defense HQ. HQ had its own issues. The police comms station hung on during the event but the rest of the complex was evacuated and judged unsafe for civil defense. They settled on a newish civic building built on seismic base isolators. A few days later it turned out that building was not safe either because it was in the collapse footprint of an adjacent tower that was found to be much less structurally sound than initially assessed.

A point not explicitly made in the executive summary is that resilience and flexibility become very important in a major event with complex and unforeseen effects.

I note a mention in the report that perhaps emergency generators for cell stations could be paid for by charging vastly inflated rates at those times. This is the opposite attitude to what is needed in a true emergency. Tens of thousands of people and businesses donated labour, food, accomodation, water, money, whatever. The dominant telco waived cell charges for those with inoperative landlines.. ie everyone in the first instance. Once the airport re-opened airlines added extra flights, at or below cost to reposition visitors and refugees out of the city and residents and helpers back in.