leak from a hose when refuelling a forklift

The incident occurred when refuelling with hydrogen a fuel cell forklift. The hydrogen was provided by a mobile refuelling station. The filling of a second forklift of the day had just begun, when a loud noise was heard and the filling hose broke, releasing hydrogen (approximately 0.14 m3). No ignition occurred.
The excess flow prevention valve was triggered. An operator pressed the emergency stop button on the control panel. The amount of released hydrogen was negliglbe, i nhe order of magniture of 10 g.

The accident caused a damage to the filling hose, coupling, and the filling port of the FC forklift, with a total damage of a million of yen. No injury occurred.

The damaged filling hose had been used 2,334 times and had been in use for approximately three years, from December 2016 to September 2019 (December 2018 to June 2019), including a suspension period until September.
An investigation by the manufacturer revealed wrinkles and abrasions due to bends on the outer surface of the filling hose. These damages were not limited to the area affected by the burst. The inner tube had fractured circumferentially.

The INITIATING CAUSE was the loss of confinement of the filling hose due to the rupture of the inner and outer layers.

The investigation found that part of the damage of the hose was coming from its storage during the movement of the mobile refuelling station: wrinkles were caused by contact with the hook of the filling cart used for storage and by the weight of the hose. Scratches were produced by contact with the storage door, valve, instruments, etc. due to vibrations while driving.
Another occasion of damage was the refuelling cycle. When the hose was attached and removed by holding only the hose during filling, the weight of the nozzle caused a kink in the filling hose. Repeated bending weakened the strength of the bent area, which was pressurised while in a deformed state. This resulted in a non-uniform pressure load and damage to the reinforcing layer.

Based on these findings, it can be concluded that the ROOT CAUSE was related to design shortcoming. It is not clear which role the spring itself plaid in the generation of (or protection from) damage. The durability test was conducted without the outer spring, because it does not contribute to the internal confinement capacity of the hose.
Finally, lack of regular inspection did not allow for an early identification of the damages.

hose

DESCRIPTION OF THE FACILITY AND THE AFFECTED COMPONENT
The production capacity of the refuelling station is unknown.
Its nominal delivery pressure was 35 MPa, in a temperature range between 5 C and 35 C.

The filling hose consisted of an innertube made of resin, a reinforcing layer made of high-strength fibre and outer cover (resin). The whole was then wrapped by a metallic spring. The purpose of the spring was to protect the filling hose's external surface, i. e. preventing mechanical damage, for example due contact with surrounding objects, to abrasions due to the hose being dragged and to deformation due to stepping on it. Moreover, the spring had also the function to prevent static electricity caused by the non-conductive layers.

The accident caused a damage to the filling hose, coupling, and the filling port of the FC forklift, with a total damage of a million of yen. No injury occurred.

The hydrogen release of this incident was due to the excessive bending of a filling hose, resulting in the destruction of the reinforcing layer. The following three reflection points regard broad discussion and actions among stakeholders (manufacturers and users):
a. Definition and standardisation of a damaging bend (when it occurs, and with which and severity)
b. Identification of the mechanism by which kinking leads to the destruction of the reinforcing layer
c. Preventions of damaging bends by means of design and operative measures.
(2) It must be understood that filling hoses are consumables. Replacement standards and inspection methods must be established and adhered to.

1. Ensuring that the minimum bending radius was not exceeded and repositioning the filling hose for easier handling when connecting.
2. Changing shape of the hook used to store the filling hose to match the curve of the hose to prevent hose wrinkles when stored.
3. Using shock-absorbing material and vibration-proof bands in mobile station vehicles to prevent damage to the filling hose due to vibrations when on the road.
4. Committing to visual inspections of the filling hoses before use and prohibiting use of any damaged hoses.
5. Establishing a rule requiring replacement of filling hoses after 2,000 fills or two years from the date of first use, whichever comes first.
6. Executing inspections by the filling hose manufacturer every six months.