Service technician working on Honda Clarity Fuel Cell at dealershipEnlarge Photo
In that marked-off 23-foot by 35-foot work area, the car is joined by a large rolling cart full of tools specific to hydrogen vehicles, a battery charger, and a set of components that are assembled into an 11-foot-high vent stack to be connected to the car.
The cart contains two 300-cubic-foot cylinders, one each of pressurized helium and nitrogen, and a portable hydrogen leak detector, along with grounding wires, high-pressure steel hoses, and such tools as a hex driver for the tank valves.
Mechanics position the car within the designated area, put it up on jack stands, electronically switch off the hydrogen supply to the fuel cell using the scan tool, and direct the fuel cell to power itself down, which takes 2 or 3 minutes.
FIRST DRIVE: 2017 Honda Clarity Fuel Cell hydrogen-powered sedan
It can take "a delicate hand" to switch off the hydrogen supply valves under the car, Reed said, which takes place during the tightly choreographed timing sequence of steps.
Once those steps have been completed, most of the danger of the fuel-cell stack producing electricity has been alleviated.
The next step is to neutralize the stack, first by filling it with helium at approximately 220 psi and pushing that through the stack and out the exhaust pipe.
Honda Clarity Fuel Cell hydrogen service equipment: tool cart and collapsed fuel venting stack kitEnlarge Photo
After again relieving line pressure, the hydrogen fuel-supply line from the tanks in the rear to the stack under the hood is then disconnected, and up to three braided venting hoses are run out of the car to the venting stack, which is grounded via a steel rod.
That process can take from 30 minutes to 3 hours, Reed said, while service personnel monitor the scan tool connected to the car's control electronics to track its progress.
When the hydrogen is largely gone from the tank itself, the rest of the car's plumbing has to be flushed to remove remaining hydrogen in its fuel lines.
That's done using a nitrogen purge function that pumps pure nitrogen through the plumbing for 5 minutes, after another sequence of valve closings and shutoffs, and vents it through the grounded stack.
Honda Clarity Fuel Cell hydrogen service equipment: collapsed fuel venting stack componentsEnlarge Photo
That's what it takes to remove hydrogen from a fuel-cell vehicle safely, leaving it with its tank locks closed and 580 psi or less of hydrogen remaining in them.
After that, Reed told us, the car is removed from the jack stands, pushed into the service bay by mechanics, and work on the system can begin.
Service items might include, for example, replacing a fuel line or valve outboard of the hydrogen tank itself—though Reed stressed that under no circumstances are the valves to the hydrogen tank ever opened during such service items.
The portable leak detector is employed several times during defueling and refueling processes, he said.
Those procedures vary in complexity, with low-pressure parts of the system forward of the tank regulator checked first for helium and hydrogen leaks after repairs are complete.
Honda Clarity Fuel Cell on lift at dealershipEnlarge Photo
Once the repair is done and those low-pressure leak checks have been passed, Reed said, mechanics go through a startup procedure that consists of a set of steps to repressurize the fuel system, including more purging again monitored via the scan tool.
Then there's a final check for any leaks in the high-pressure parts of the fueling system
Once the car's fueling system is fully operational, the 0.5 kg of remaining hydrogen in its tanks should be enough to take it to the fueling station nearest the dealership, he said. This means dealers don't keep stocks of hydrogen fuel on-hand, a frequent question on the topic.
The bulk of hydrogen fuel-cell mechanics, Reed said, have previous experience with natural-gas vehicles, which Honda sold from 2002 through 2015 in three generations of Honda Civic compact sedans.
They're familiar with nitrogen purging, pressure regulators, valves and O-rings, and other hardware associated with high-pressure compressed gaseous fuels.
EDITOR'S NOTE: We have updated this article to clarify some points after further discussion with Honda's Doug Reed; we thank him for his efforts.