Analyzing the Safety Aspects of Onsite Hydrogen Generation Versus High Pressure Cylinders for Use in GC Applications

Permitting and safely managing inventories of flammable hydrogen is a common concern in a laboratory. Laboratories can choose to install an on-site hydrogen gas generator or have bottled hydrogen gas delivered to the workspace and stored in classified areas.

GC practitioners who use hydrogen need to take precautions to ensure the safety of their laboratory, as an unintended leak due to downstream equipment failure can quickly create an explosive atmosphere; several incidents have been reported (1). Hydrogen in air can ignite when exposed to the energy in a static discharge, as low as 0.017 mJ; the Lower Flammability Limit (LFL) is 4% H₂ in air, by volume (2). Frequently replacing depleted high-pressure hydrogen cylinders creates a chance for accidents.

More than one standard H₂ cylinder exceeds code minimum limits, imposing special building construction, separation distances, and increased facility costs — especially when co-located with other research gases (3,4). One standard H₂ cylinder, storing 6300 liters of H₂ gas, has the explosive potential of 35 lb of TNT.

Comparative Analysis:

The Proton OnSite® HOGEN® GC600 hydrogen gas generator can serve up to five typical GC instruments continuously with FID fuel and carrier gas. Internally, it contains less than 3 liters of H₂ at any time. Table I shows that the GC600, with a maximum H₂ flow rate of 600 cc/min, was allowed to flow unchecked into a 3000 ft³ laboratory space with 12 air changes per hour (5).

Table I: Hydrogen dispersion over time

In comparison, a standard DOT 3AA-2400 H₂ gas cylinder can serve the same 5 GC instruments for up to 65 h before it must be replaced. Table I also shows the 6300 liter contents of a single H₂ cylinder were to be released unchecked in the same 3000 ft³ laboratory space.

Figure 1: Hydrogen release dispersed in a 3000 ft3 laboratory space outlined in Table I. The Standard DOT Gas Cylinder’s release very quickly exceeds LFL. The Proton OnSite HOGEN GC600 release of hydrogen fails to come near to dangerous levels even after an extended period of time.

Conclusions

GC practitioners must manage hydrogen supplies with the utmost care to avoid leaks and releases, which can quickly create an explosive atmosphere in a laboratory. But, even without proper due diligence, the checks and balances within Proton's listed HOGEN hydrogen generators mean a release will not meet hydrogen's LFL levels, as opposed to a standard H₂ cylinder which, if left unchecked, could create a dangerous atmosphere in less than 3 min.

References

(1) PNNL, H2 Incident Reporting, laboratories, http://www.h2incidents.org/sort.asp?cat=2&val=1.

(2) Basic considerations for the safety of hydrogen systems, ISO/TR 15916:2004.

(3) NFPA 55, Compressed Gases and Cryogenic Fluids Code.

(4) NFPA 2, Hydrogen Technologies Code.

(5) ASHRAE 62.1-2010 minimum 12 ACH rate for science labs based on 0.18 cfm/ft² floor area, with a 9 ft ceiling.

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