Appropriate Use of Gas Systems – DOs and DON’Ts

DO

  • Train all new users (and re-train existing users, where necessary) in the proper way to attach and remove a regulator to and from a gas cylinder, and how to check for leaks.
    • View EH&S’ safety video. [link]
    • Document all safety-related training, including hands-on training as part of the PI’s internal training records.
  • Ensure that all gas equipment has clear SOPs detailing proper operation.
    • This is especially important for systems that include safety-critical equipment which rely on correct operation by user for their effectiveness (e.g., a cross purge setup).
  • Use the minimum possible pressures for any work being performed.
    • High pressures always result in greater hazards.
    • High pressures can’t always be avoided. If they must be used in experiments, be aware of the potential energy release and ensure all equipment is:
      • Adequately engineered to withstand the pressure, AND
      • Protected from over-pressure by safety devices such as bursting discs and automatic pressure relief valves of sufficient flow rating, AND
      • Blast-shielded to prevent projectile hazards (don’t forget to shield against flying pieces of bursting disc!).
    • If using high pressures, remember to:
      • Specify appropriate PPE in the SOP. Depending on the hazard and risk, this might include hearing protection, face shield, hand protection, and potentially even body protection (though if body protection is considered necessary, re-evaluate the adequacy of engineering safety controls such as blast shielding). AND
      • Have a contingency plan in place to respond to system failures.
  • Design your equipment setup with adherence to the following:
    • Consider the various properties of the gases being used and select the equipment best fit to handle them.
    • Familiarize yourself with equipment specifications and operating manuals provided by manufacturers of gas equipment.
      • Retain documentation and use it as part of internal training, for example, by including it in SOPs.
      • Ensure equipment is used within manufacturer’s specifications. For example, do not use devices above their maximum pressure rating and check material compatibility before using devices with gases which are corrosive, toxic, oxidizing, or which may explosively decompose (e.g., acetylene).
  • When working with complicated equipment, consider creating a checklist which is easy to reference to prevent user error when operating equipment.
    • Consider numbering all the valves and other controls and referencing that to the checklist. As an example, this could prevent explosive gas-air mixtures from forming as a result of incorrect valve operation.
  • If work involves high-pressure reaction vessels, e.g., “Parr™ bombs” for combustion calorimetry, hydrogenation, etc., always:
    • Follow the manufacturer’s operating instructions. NOTE: Incorporate instructions into an SOP.
    • Ensure combination of solid/liquid fill volume, initial gas pressure, and maximum temperature are within manufacturers guidelines to prevent peak pressures on heating (thermal expansion of gas plus vapor pressure of liquid) from exceeding safe limits.
      • Never over-fill with liquid; hydrostatic pressure from liquid expansion may over-pressurize the vessel.
      • If chemical reactions produce heat or gas, perform modeling to ensure possible thermal runaway will not result in over-pressure.
    • Ensure the vessel is properly assembled each time it is used. Ensure that the compatible bursting disc (and anti-corrosion disc, if present) is in place.
    • Inspect regularly for signs of corrosion or damage.
    • Send back to the manufacturer for inspection/testing/repair if: (a) corrosion or damage is evident, (b) over-pressurization is indicated (as evidenced by failure of the bursting disc), or (c) vessel might have overheated.
    • Create a log book for each vessel to chronicle use. This ensures that fatigue limits (time or number of pressurization cycles) or de-rating maximum allowable pressure (after a certain amount of use) as specified by the manufacturer are respected.
  • Avoid creating “suck-back” when using a bubbler system.
    • Avoid creating negative pressure when the bubbler is open. The three most common ways this happens are as follows1:
      • Pulling a vacuum on the system when it is open to the bubbler.
      • Turning off the heat on a hot reaction but not increasing the gas flow.
      • Cooling the reaction in a cold bath but not increasing the gas flow.
    • For oil bubblers, a one-way check valve rated for the pressure can be installed to prevent suck-back.2
    • A secondary vessel to intercept sucked-back liquid can be placed between a bubbler and the rest of the system.2
    • Bubblers with an integral, non-return valve can be used, including the spring-loaded “over-pressure” design which also has the advantage of allowing a higher gas pressure. These prevent suck-back, but they are more expensive.2
  • If gases are used with tube furnaces, ensure the outlet cannot become blocked.
    • A tube furnace exploded because excess glass wool was compacted at the outlet end of the silica glass tube. Over-pressurization occurred and consequently, the tube burst.

DON’T

  • DO NOT use glass equipment at pressures significantly above atmospheric.
    • All glassware under pressure is at risk of sudden catastrophic failure.
    • For large vessels, even 1 psi above atmospheric (“1 psig”) may put the glass under significant tensile stress.
    • If glassware must be used under pressure:
      1. Perform a risk assessment.
      2. Keep internal volumes as small as possible.
      3. Use thick-walled equipment.
      4. Use shielding against possible flying glass fragments.
      5. Always wear eye protection.
      6. Document safe work practices in an SOP, provide training to users, and keep internal training records.
    • For more information on glassware safety, visit the Glassware Safety webpage.
  • DO NOT store flammable or oxidizing gases near ignition/heat sources, electrical panels, or unprotected electrical connections.
  • DO NOT allow flammable gas/air mixtures to form within vessels or enclosures.
    • Case study: University of Missouri – Columbia incident.
    • Always remove air by purging with inert gas or by evacuating before admitting flammable gas.
    • Do not place flammable gas systems or pipework in enclosures; a small leak may cause an explosive atmosphere to form within.
    • Very careful equipment design is required if explosive gas mixtures are to be intentionally produced. This requires elimination of all ignition sources (e.g., static discharges) and to ensure safety in the event the mixture does explode.
      • Expert engineering assistance may be required at the design stage.
      • Catastrophic case study which resulted in loss of an arm: University of Hawai’i incident.
  • DO NOT use fittings and tubing that are incompatible with: (a) each other, (b) the gas, or (c) the maximum pressure.

Citations

  1. Toreki , R. (no date) The glassware gallery: Bubblers, Interactive Learning Paradigms, Inc. . Available at: http://www.ilpi.com/inorganic/glassware/bubbler.html (Accessed: 12 July 2024).
  2. Bubblers (2023) The Schlenk Line Survival Guide. Available at: https://schlenklinesurvivalguide.com/bubblers/ (Accessed: 12 July 2024).