8. Flammable and oxidising gases must be segregated with atleast 20 feet or 6 meters away from each other.
9. The cylinder must be located away from other hazards. Maintain an exclusion zone around a cylinder as per the standard given below.
10. The cylinders come with a valve guard. This protects the cylinder valve in case the cylinder falls. Please keep it on if the cylinder is not being used.
11. Always install the cylinder with an output pressure gauge and shut off the valve. The former ensures that unsafe pressure is not maintained in the line. The latter is useful in an emergency where the gas supply needs to be turned off.

5. A well-designed cylinder cart is the only safe method to move cylinders in corridors and between labs. The cylinders must be strapped to the cart. Never “roll” the cylinders.

1. IISc follows NFPA 704 nomenclature to define “hazardous”. Any gas with an NFPA rating > 2 in any category is considered hazardous.
2. The higher rating implies that the gas is more dangerous than inert compressed gases due to chemical activity, flammability, explosivity, toxicity, or pyrophoricity. Hazardous gases need additional safeguards.
3. Some examples of hazardous gases are hydrogen, silane, germane, arsine, diborane, phosphine, metal-alkyls, etc.

1. Hazards scale with pressure and quantity. Large cylinders at high pressure can carry up to 10 m3 of gas. Evaluate if a smaller cylinder with lower pressure will suffice for your experiment. Details will be specific, but as an example, consider the following options for hydrogen.
   • Replace 100% hydrogen with 5% hydrogen diluted in nitrogen (called forming gas). Below 5%, H2 is intrinsically safe, even at high pressures. So, there is no need for additional safeguards beyond those prescribed for compressed nitrogen. This is the most cost-effective and straightforward solution.
   • Consider purchasing low-pressure cylinders. For example, H2 gets more dangerous when stored amount exceeds 1% of the laboratory volume at standard pressure. A 40 m3 lab remains safe from ignition hazard, even in the case of a catastrophic release, if it stores less than 400 litres of H2 . That translates to a 40-litre cylinder at 10 bar.
2. Tabletop H2 generators are an easy solution for small quantities of H2 . They are intrinsically safe and don’t require any special precautions. Prices start at two lakhs. For the pressurised Parr reactions (in the room with autoclaves), consider generators that produce higher pressures, e.g., https://thalesnano.com/phoenix-h-genie-platform/

High-pressure H2 (>4 bar) must be used with proper safeguards. A system must have at least one barrier to prevent a top event and one barrier to mitigate the effect of a top event. Safeguards must also be added to avoid the degradation of a critical barrier. A safety bowtie is a helpful way to visualise this. On the left are preventive barriers, and on the right are mitigation barriers. The analysis is usually the result of a formal HAZID/HAZOP study. OLSEH can help organize these studies for complex systems.

The following basic safety systems are needed for all hazardous gases at pressure (including low-pressure cylinders recommended above)

1. Basic cylinder safety: The Usual requirements for any compressed gas cylinder must be followed, e.g., restraints, labels, etc.
   • As a corollary, cylinders should be transported safely in carts. No rolling.
   • Get cylinders from reputed vendors.
2. Regulators. To step down the pressure for distribution. The output pressure should not be > 8 bar. The use of hazardous gases at higher pressures requires advanced safety features.
3. Flash arrestors: If a flammable gas is being used in an open circuit (at some point, gas vents to air without scrubbing), then inlet lines must have flash arrestors. If flash arrestors are not possible, for example, due to purity requirements, the lines must be closed in a loop with a scrubber at the end.
4. Outlet valves and fittings: All distribution lines should have a high-pressure diaphragm or ball valve made of metal (chemically compatible with the gas). Avoid using low-cost valves from a hardware store. All fittings, tubes, and valves must be made of metal—no insulating materials like plastic/rubber that can cause static.
5. Earthing: Flammable hydrides are highly susceptible to static electricity. All flammable cylinders and lines must be earthed. If the lines use insulating gaskets, such as rubber, then individual sections of the metal line must also be grounded.
6. Access-control. Cylinder change is a critical maneuver. Mistakes can be deadly. Only authorised and trained personnel are allowed to change cylinders. The labs must have some form of access control (e.g., lock, room) to prevent unauthorized changes to cylinders
7. Log register. A log register must be maintained with the following information.
   • Date of installation with cylinder number; initial quantity of gas in std. litres; cylinder pressure.
   • For every usage, there should be an entry with date, starting cylinder pressure, and volume used in std. litres; final cylinder pressure; & username.
   • Date of removal of the cylinder; final pressure.
8. At a minimum, the gas manifolds must have a purge cross. The purge is used to evacuate residual air during cylinder changeover. Extremely hazardous gases, such as SiH4 , will require more complex manifolds with 5 or 7 valves, which are discussed in the next section.
9. Consider passive flow restrictors that limit flow to a low value, like 1 litre/min. These can be simple orifices with an appropriate diameter.
10. Sensors: All hazardous gases require interlocked sensors. These must be continually active sensors, mounted near the cylinder and usage point. The sensor’s output should be connected to a siren and a building fire alarm system. In the event the sensor detects a leak, the departments must evacuate. Handheld sensors can be used to detect manual leaks during delivery and after transportation.

In cases where pressure is very high (> 8 bar) or if the NFPA rating in any category is 4, additional safety features are required (in addition to those mentioned above). Details may vary, but we must follow the attached checklist. The department is welcome to submit a plan to OLSEH for consideration. The design of all gas distribution systems of such a system must be certified by two faculty members (with suitable expertise), other than the PI, OR approved by OLSEH

1. Gas-cabinets or gas-banks: High-pressure hazardous cylinders should be stored outdoors in a well-ventilated area whenever possible. The gas can be distributed from the gas bank to the labs using SS pipes. Design the gas-bank well. Gases like H2 tend to accumulate near the roof. The electrical fitting near the cylinders of flammable gas must be explosion-rated. Alternatively, the cylinder should be installed by a professional gas-cabinet installer. The gas cabinets may be either completely automatic or semi-automatic, shutting off the gas flow from the cylinder in the event of alarms or gas leaks.
2. Cylinder manifold: All high-pressure hazardous gas cylinders must be connected to a 5-valve or 7-valve purge manifold, rated for the gas. Professionally constructed manifolds are commercially available. Don’t design your own. Manifolds are often built into professional gas cabinets.
3. Certification for the cylinder. H2 causes embrittlement of metal. Any H2 cylinder must be certified by a reputable manufacturer for storage of H2 . This often means regular isostatic testing. In cases where the certificates are not available, the cylinder must be discarded every 5 years of use.
4. Non-arcing tools: For flammable gases, use non-arcing tools for cylinder change or line repair.
5. Gas distribution system: Gas distribution on the manifold must be constructed using fittings rated for H2 . We strongly prefer welded, face-seal fittings (VCR® or equivalent). High-quality Swagelok® or other compression fittings with metal ferrules are also okay, if installed professionally. No plastic tubing. All lines must be He-leak checked after installation or repair.
6. Active fire-fighting equipment: To contain a fire, flammable cylinders must have active fire-fighting systems, e.g., sprinklers. A sprinkler in the vicinity of an H2 cylinder is mandatory.
7. Documentation:
   • A clearly written SOP for common events like cylinder changes and transportation. OLSEH must approve the SOP. A template is available on request.
   • A list of users who have been trained to change cylinders with dates of their training.
8. Depending on the capacity, autoclaves or other high-pressure equipment themselves might require safety paraphernalia like reinforced walls.

Cylinder and valve integrity may be compromised by improper storage and handling. General storage and handling conditions for all gas cylinders include the following:

1. Cylinders should be stored in well-ventilated areas
2. Always wear eye protection rated for protection from impact (i.e., ANSI Z87+ rated) while using or handling compressed gases
3. Cylinders of liquefied gases should be stored upright, unless there are specific directions on the cylinder indicating otherwise. Examples of liquefied gases include, but are not limited to, nitrogen, acetylene, carbon dioxide, ammonia, chlorine, hydrogen sulfide, and hydrogen chloride. Liquified gases also contain higher volumes of gas at room temperature and pressure than the same-sized cylinder of a compressed gas and thus present a greater asphyxiation potential or valve guard
4. Cylinder caps must be in place whenever regulators are not attached.
5. All gas cylinders need to be chained to the wall. The chain must either be at half height or two chains at 1/3 and 2/3 height (Figure 9.2). This ensures that the cylinder stays vertical in the event of cylinder valve failure, preventing it from flying through the walls like a missile.
6. Store cylinders away from corrosive materials (e.g., acids and bases), which can damage the cylinder
7. Store gas cylinders away from sources of heat.
8. Store empty cylinders away from full cylinders. Ensure that empty cylinders are labeled as such and are returned promptly to the manufacturer
9. Ensure that gas cylinders are stored such that they do not obstruct means of egress, electrical panels,eye washes, drench showers, access to hazardous materials, or other items.
10. Never move or use a compressed gas cylinder unless you have been provided with hands-on instruction from your PI or trained and authorized coworkers on how to do so.
11. Don’t roll the cylinders; use a trolley with wheels (Figure 9.3)
12. Cylinders must be transported on approved carts, with the strap/ chain in place, and with a cylinder cap. Minimise walking with cylinders. Only walk with cylinders for very short distances to move them from the cart to the final storage location.
13. Regulations govern the storage of compressed gases. Permanent and temporary storage cylinders must be tested and certified at the prescribed schedule.

If a gas cylinder, containing a toxic, flammable, pyrophoric, or corrosive gas, ever develops a leak, then:

1. As a rule, the fuel gas loading should not exceed 1 kg per 25 m2 of floor space in well-ventilated laboratories.
2. The laboratory storage of replacement (disposable) gas cylinders should be kept to a minimum and restricted to less than 1.5 kg. Any sources of ignition are eliminated near the gas cylinder when not being used.
3. Use the cylinders only in well-ventilated areas.
4. The fire load of other hazards present inside labs must be low.
5. Labs should have secondary emergency exits.
6. The minimum distance between flammable and oxygen gas should be 20 feet or 6 meters.
7. Keep the cylinder valves closed when not in use
8. Ensure that the cylinder is always stored upright (vertical) and is not at risk of tipping over.
9. Inspect the cylinder on a regular basis to ensure it is in good condition, free from rust, and housed properly
10. Ensure the cylinder is stored in an area that is adequately ventilated and not susceptible to excessive temperature rise.
11. Store the cylinder in a secure location to protect against falling, damage, being hit by etc.
12. Provide separate storage for LPG away from the oxidizing gases (e.g., oxygen) by at least six meters.
13. Do not store the cylinder near an ignition source, or in locations that could jeopardise escape from the building in the event of a fire.
14. “NO SMOKING” sign board to be placed near the cylinder storage area
15. All kinds of hot works should be restricted in such labs with an LPG cylinder.
16. The flammable gas cylinders should not be placed near the entrance/exit to the lab.