| Related Documents |
| EHS Door Sign Request Form EHS Waste Pickup Request Form EHS Supplies Request Form Completing the Hazardous Waste Manifest Work Connections Injury or Illness Report |
20.1 Introduction #
All University of Michigan (U-M) employees ordering, handling, using, or storing compressed gas cylinders (cylinders) must comply with the requirements contained in this document and complete all required training. A compressed gas means a gas or mixture of gases contained under pressure exceeding 40 psi at 70°F. The topics in the body of this document pertain to all compressed gases and compressed gas cylinders.
Reference Regulations:
Welding and Cutting (MIOSHA General Industry Part 12)
Compressed Gases: Acetylene, Hydrogen, Oxygen, & Nitrous Oxide (MIOSHA General Industry Part 69)
International Fire Code Code Development (NFPA 55)
20.2 Compress Gas Hazards #
The potential hazards of compressed gases and their associated cylinders are as follows:
• Fire and explosion hazards of flammable, pyrophoric, or reactive gases.
• Health hazards of toxic, corrosive, or asphyxiant gases.
• Pressure hazards due to the high pressures within most cylinders can result in rapid release and subsequent violent pin wheeling or propulsion (rocketing) of the cylinder.
• Safety hazards, due to the weight of the cylinders, during handling and storage operations.
20.3 Training Requirements #
All U-M personnel must follow the best practices written for your department. All research laboratory personnel working in a laboratory that uses hazardous materials must successfully complete theEHS_BLS025w General Laboratory Safety Training course. In addition, they must read and follow the standard operating procedures written for the lab regarding safe use of compressed gases.
20.4 Restricted Hazardous Gases #
Restricted hazardous gases present an increased risk to personnel and for the University of Michigan; therefore, personnel must obtain EHS approval before ordering the following gases:
- Carbon monoxide
- Pyrophoric gases (e.g. arsine, disilane, diborane, germane, phosphine, silane)
- Flammable gases (e.g. Hydrogen)
- Toxic and highly toxic gases per NFPA 55
- Oxidizers (e.g. liquid oxygen, gaseous oxygen >25%, chlorine, fluorine)
- Corrosive gases (e.g. ammonia)
Required Approval Process #
Approval must be obtained to purchase the following hazardous gases, in cylinder sizes larger than a lecture bottle (size LB): carbon monoxide, flammable gases, corrosive gases, liquid oxygen, oxidizers (i.e. nitrous oxide, oxygen > 25%), hydrides (i.e. arsine, disilane, diborane, germane, phosphine, silane), and toxic and highly toxic gases per NFPA 55.
The following departments are exempt due to restrictions and audits through separate programs: Lurie Nanofabrication Facility (LNF), B&F Facilities and Operations, Hospitals and off-site clinics, Unit of Laboratory Animal Medicine (ULAM) and School of Dentistry patient clinics.
To purchase any of the restricted gases, departments must complete a Chemical Requisition Form by clicking the “+Add” button on the Mi Safety Portal (MISP) Chemical Requisition page. Environment, Health & Safety (EHS) will approve requisitions within MISP and email the approval to the requester and noted supplier. The purchasing unit will provide the MISP chemical requisition number to the supplier as the approval number. Contact EHS at (734) 647-1143 or visit Compressed Gas on their website for additional information. See the Procurement Services website for the current university gas contracted suppliers.
When logged into MISP, the link will open directly. If not logged into MISP, you will be prompted to login first, then click the link a second time to open the form.
For more information, refer to the Restricted Hazardous Gases Authorization Form.
20.5 Maximum Allowable Quantities #
National Fire Protection Association (NFPA) 55 and International Fire Code have established a maximum allowable quantity (MAQ) of compressed gas that can be used and stored within a building. Therefore, use the following best management practices to minimize the amount of compressed gas located in your workplace.
- Substitute, if possible, with a gas that is less hazardous.
- Limit the amount of hazardous compressed gas to that which is deemed necessary.
- Minimize the quantity of compressed gases on hand using the following strategies:
- Maintain the smallest quantities of compressed gases as possible
- Have no more than one backup cylinder of each gas
- Use just-in-time delivery
- Record all compressed gases in your chemical inventory, including non-hazardous gases
The Restricted Hazardous Gas Policy controls the quantity of hazardous gases in a building. MAQs vary based on factors such as the floors above grade, quantity and type of gas used and stored, fire control zones, and sprinkler protection.
Contact EHS at (734) 647-1143 to assist you and the facilities manager to determine the MAQ for your lab or workspace.
20.6 Compressed Gas Cylinder Labels #
Do not accept a cylinder from the gas supplier without a proper label. Cylinders must be legibly marked by stenciling, stamping, or labeled with at least the chemical name (or commonly accepted name of the material contained) and the primary hazard associated with the chemical (such as “flammable”).
In addition, the cylinders must bear the approved markings of the Department of Transportation (DOT)
stamped in the metal at the top of the cylinder.
NOTE: Do not rely on the color of the cylinder for identification of contents as colors may vary with supplier. Look at the official label on the cylinder, not the color of the cap.
20.7 Uses #
When using, transporting, moving, and storing compressed gases cylinders, follow these best practices:
- Cylinders must not be refilled except by authorized suppliers.
- Repair or alteration of a cylinder is prohibited.
- Only properly trained employees should handle and use compressed gas cylinders.
Using Compressed Gases #
- Never use an open flame or smoke in areas where oxygen or flammable gases are used.
- Never heat a cylinder to raise the pressure of the gas.
- Never leave pressure on a hose or line that is not being used.
- Leave some positive pressure (a minimum of 20 psig) in empty cylinders to prevent “suck back” and contamination.
- Never use compressed gas to dust off equipment or clothing.
- Never use a tool to force open a stuck valve. Contact the gas supplier for assistance.
Transporting Cylinders #
- Use a gas cylinder hand cart and the proper restraining devices to move cylinders more than one meter. Never drag, slide, or roll a cylinder.
- Transport a cylinder with its protective cap in place.
- Do not use a valve cover to lift a cylinder.
- Never drop, bang, or strike cylinders against each other or other objects.
Inspecting Cylinders #
Cylinders and their associated equipment must be inspected before each use.
- Cylinders
- The cylinder label must identify the gas or gas mixture and the primary hazard associated with that chemical (flammable, oxidizer, etc). Do not accept a cylinder without a proper label; contact your supplier.
- The cylinder must be free of corrosion, pitting, cuts, gouges, bulges, neck defects and general distortion.
- Associated equipment
- The cylinder mounting and restraining devices must not show any signs of damage or loss of integrity.
- Use only the regulator designed for the gas being used. Do not force corrections.
- Do not use Teflon tape on any CGA valve connection threads. Tape will prevent the bullet-nose CGA from fully contacting the mating surface inside the cylinder valve, increasing the chance of a gas leak.
- Valves and regulators must not show signs of damage (cracks, corrosion, etc). If they do, contact the supplier.
- Cylinder regulators and connections must be tested for leaks.
- For argon, nitrogen, hydrogen, or air, use a soapy water solution to test for leaks.
- For oxygen, only leak-test solutions specifically designed for oxygen compatibility may be used to test for oxygen leaks; do not use soap solutions because they may contain oils that can react violently with the oxygen.
- For other gases, leak test the lines and equipment with an inert gas before using.
When inspecting cylinders and associated equipment after use, verify the following actions have been taken:
- Valves are closed and tightened.
- Any remaining residual gas has been safely released from the line.
- Valve protection caps are securely fastened during long-term storage.
NOTE: Any problem with pressure-relief devices should be immediately reported to your supplier. Never tamper with pressure-relief devices in valves or cylinders. Only qualified gas supplier personnel should service pressure-relief devices.
Responses to Identified Problems #
If at any time you notice a problem with a cylinder or its associated equipment, contact the supplier for technical advice, replacement, or both.
If you identify a leak that you cannot fix and the cylinder contains hazardous material, call DPSS at 911 and evacuate the area.
20.8 Engineering Control Measures #
The following engineering controls must be implemented when using, transporting, moving, and storing compressed gas cylinders:
- Secure cylinders and lecture bottles in an upright position using the appropriate restraining devices. NOTE: Securing devices for various sizes and shapes of compressed gas cylinders can be purchased from gas suppliers or safety equipment companies.
- Ventilate areas where the cylinders are used and stored.
- Install, where required, the following engineering control measures:
- Continuously exhausted gas cabinets or enclosures.
- Gas detection systems, alarms, etc.
- Nitrogen purge system.
- Automatic shut-off valves.
- Flashback arrestors.
- Place and tighten the valve protection cap on the compressed gas cylinder when the cylinder is not in use.
- If using flexible (non-fixed) tubing, the tubing must be under 10 feet in total length. Contact EHS at (734) 647-1143 to assist you and the facilities manager to determine the proper engineering controls for your lab or workspace.
Fixed Pressurized Piping #
All compressed gases distributed in fixed pressurized piping and with any of the following properties (1) health hazard ratings of 3 or 4; (2) a health hazard rating of 2 without physiological warning properties, or (3) a reactivity rating of 3 or 4; or are (4) pyrophoric or flammable with a flammability class 4 rating must have the following engineering controls:
- Excess flow control devices.
- Continuous gas monitoring.
- Automatic shutoff valves
NOTE: This information is for general guidance. Consult with EHS to determine requirements for your particular usage. A code analysis may also be required.
20.9 Administrative Controls #
The following administrative controls must be implemented when transporting, moving, and storing compressed gases cylinders.
- Replace or remove damaged or compromised cylinders or equipment.
- Use the associated equipment that is “assigned” to the compressed gas cylinder.
- Display the appropriate signs and labels in locations where cylinders are stored or used. For laboratories, contact EHS at [email protected] to request hazard warning labels. To request a door sign, go to the EHS Door Sign Request Form.
- For laboratories, be familiar with the U-M Chemical Hygiene Plan (CHP).
- Write and implement SOPs about using, transporting, moving, and storing compressed gas cylinders in the work location.
- Never perform lab work alone with hazardous gases. Always implement a buddy system if work is conducted outside of normal business hours.
- Promptly return unneeded or excess gas cylinders to their vendor. Avoid stockpiling cylinders not needed for immediate use. Excessive storage can lead to fire code noncompliance and result in costly cylinder rental fees.
20.10 Personal Protective Equipment #
The following list of personal protective equipment (PPE) is required to help ensure your safety when using, transporting, moving, and storing compressed gases cylinders. For specific information, refer to the chemical’s safety data sheet and your department’s SOPs regarding PPE.
- Wear safety glasses or goggles for all work involving compressed gas cylinders.
- Wear steel toe shoes for frequent handling of compressed gas cylinders.
- Wear the proper protective clothing as stated in your department’s SOP.
- Use the proper equipment as stated in your department’s SOP.
20.11 Storage Requirements for Compressed Gases #
Cylinders not “in use” must be stored in a location separate from the workspace. A cylinder is considered to be “in use” if it complies with one of the following:
- Connected through a regulator to deliver gas
- Connected to a manifold being used to deliver gas
- A single backup cylinder secured alongside a cylinder that is connected through a regulator to deliver gas
For long-term storage of a cylinder, comply with the gas supplier’s recommendation. In general, do not use a cylinder for more than three years at which point it must be returned to the supplier for testing and certification.
Other storage requirements are as follows:
- The storage location must be dry and well-ventilated.
- Cylinders must be grouped by the type of gas and segregated by compatibility.
- Full cylinders must be separated from empty cylinders with the empty cylinders marked with the word “Empty”.
- Flammable gases must be stored away from flammable liquids, combustible materials, oxidizers, open flames, sparks and other sources of heat or ignition.
- Oxygen cylinders in storage must be separated from fuel-gas cylinders or combustible materials (such as grease) by a minimum distance of 20 feet or by a noncombustible barrier at least 5 feet high having a fire-resistance rating of at least one-half hour
- Oxygen and flammable gases must be stored separate from locations where open flames and smoking are present. “No Smoking” and “No Open Flames” signs must be conspicuously posted in these areas.
- Cylinder valves must be closed when the cylinder is not in use.
- Removable caps must be on the cylinders at all times, except when cylinders are in use.
- Caps used for valve protection must be secured when the compressed gas cylinder is not being used and before moving the cylinder.
- Empty cylinders must be stored with the valve protection cap securely in place.
- Damaged or defective cylinders must be removed from service (contact the cylinder vendor or supplier for assistance).
- The temperature of the storage location must be maintained within the temperature range allowable for the cylinder as specified by the manufacturer (generally speaking, the temperature of gas cylinders must stay below 125°F).
- Pyrophoric, toxic, and corrosive gases must be stored in a continuously mechanically exhausted ventilated enclosure.
Where NOT to Store Cylinders #
Cylinders must be stored in locations that are free from clutter and where they are easily accessible.
| DO NOT STORE CYLINDERS… | TO PREVENT… |
| Hallways, corridors, stairwells, near elevators, or any other high traffic areas. | Cylinders from being knocked over or tampered with. |
| Areas that are exposed to continuous dampness or areas that are used to store salt or other corrosive chemicals or fumes. | Cylinders from physical damage. |
| Outside unless they are appropriately sheltered or covered. | Cylinders from corroding. |
| In cold rooms or other unventilated spaces such as closets, lockers, trenches, tanks, and confined spaces.NOTE:An exception may be approved by EHS for inert gases when an oxygen monitor is in place. Contact EHS at (734) 647-1143 for more information. | A build-up of gas in a storage location.Oxygen deficiency. |
| In direct sunlightIn excessive heatNear sources of ignition (such as flames or sparks)Near combustiblesWhere they might become part of a electrical system | An increase of pressure inside a cylinder resulting in an explosion or fire. |
20.12 Waste Disposal #
In most cases, the compressed gas cylinder, including any unused gas, will be returned to the supplier from which the cylinder was purchased.
For gas cylinders that cannot be returned to the supplier, contact Environment, Health & Safety, Hazardous Materials Management (HMM) at 734-763-4568 or fill out the online form to arrange for collection. Write “empty” on the outside of each cylinder and complete a hazardous waste manifest.
20.13 Hazards of Common Compressed Gases and Hazard Controls #
Hazards of Common Compressed Gases #
The following table1 is a partial listing of some of the more common compressed gases and their associated hazards. Many gases exhibit more than one hazard. To provide the best protection to the user, a gas’s most severe hazard has been designated with a “P” for primary. Any additional hazards for which added precautions are recommended have been designated with an “S” for secondary.
The hazards have been grouped into six general categories: flammable, asphyxiant, oxidizer, toxic, corrosive, and extreme cold. The following is a detailed description of each category and how a gas is classified.
- Toxic: In all cases, if a gas is toxic, this is the primary hazard. A toxic gas is any gas that has an LC50 less than or equal to 2,000 ppm, but greater than 200 ppm. A highly toxic gas is any gas that has a LC50 in air of 200 ppm or less.
- Flammable: Any gas for which flammable limits in air are reported is considered flammable. However, if the gas were also toxic, then toxic would be the primary hazard with flammable noted as secondary.
- Asphyxiant: This category generally covers all the inert and noble gases. A gas that is listed flammable as primary would usually be listed with asphyxiant as secondary, especially if any reported toxicity approached oxygen-deficient levels.
- Oxidizer: This covers those gases that, in the presence of an ignition source and a fuel, support and may vigorously accelerate combustion. If the gas was also toxic, this would be listed as primary hazard with oxidizer as the secondary hazard. Some gases, such as fluorine, are as aggressive an oxidizer as they are toxic, so both hazards are listed as primary.
- Corrosive: Primarily, most gases in the absence of water are not corrosive. However, since most sources refer to the gas properties in moist air, corrosive is listed as a mostly secondary hazard where appropriate.
- Extreme Cold: If a gas is shipped as a liquefied gas under pressure, extreme cold would generally be listed as a secondary hazard, assuming there are more significant (primary) hazards. However, an inert cryogenic liquid is listed with extreme cold as its primary hazard.
- Other: Other hazards are included in this category. If a gas has pyrophoric properties, severe decomposition hazards, or other types of reactivity hazards, they are referenced in this column. A description of the numbers found in this column is located at the end for this table.
NOTE: The user is cautioned that other classification systems exist, particularly from regulatory agencies that may result in a different assessment of the hazard. In addition, there may be additional health hazards that are not reported here, so the user should consult the gas supplier’s SDS for specific information.
| GAS/CAS NUMBER | FLAMMABLE | ASPHYXIANT | OXIDIZER | TOXIC | CORROSIVE | EXTREME COLD | OTHER* | DOT CLASS2 |
|---|---|---|---|---|---|---|---|---|
| Acetylene / 74-86-2 | P | S | 1 | 2.1 | ||||
| Air, Compressed / NA | 2.2 | |||||||
| Ammonia / 7664-41-7 | S | P | S | 2.3, 8 | ||||
| Argon / 7440-37-1 | P | 2.2 | ||||||
| Argon (Liquid) / 7440-37-1 | P | S | 2.2 | |||||
| Arsine / 7784-42-1 | S | P | 2.3, 2.1 | |||||
| Bromochlorodifluoromethane (R12B1) / 353-59-3 | P | 2.2 | ||||||
| 1,3-Butadiene / 106-99-0 | P | S | S | 3 | 2.1 | |||
| Butane / 106-97-8 | P | S | S | 2.1 | ||||
| 1-Butene / 106-98-9 | P | S | S | 2.1 | ||||
| Carbon Dioxide / 124-38-9 | P | 2.2 | ||||||
| Carbon Dioxide (Liquid) / 124-38-9 | P | 2.2 | ||||||
| Carbon Monoxide / 630-08-0 | S | P | 2.3, 2.1 | |||||
| Chlorine / 7782-50-5 | S | P | S | 2.3, 8 | ||||
| Chlorine Trifluoride / 7790-91-2 | P | P | S | 2 | 2.3, 5.1, 8 | |||
| 1-Chloro-1,1 –difluorethane(R142b)/ 75-68-3 | P | S | S | 2.1 | ||||
| Chlorodifluoromethane (R22) / 7545-6 | P | S | 2.2 | |||||
| Chlorotetraflurorethane (R124) / 2837-89-0 | P | S | 2.2 | |||||
| Chlorotrifluoromethane (R13) / 75-72-9 | P | S | 2.2 | |||||
| Cyanogen / 460-19-5 | S | P | S | 2.3, 2.1 | ||||
| Cyclopropane / 75-19-4 | P | S | S | 2.1 | ||||
| Diborane / 19287-45-7 | S | P | 4 | 2.3 | ||||
| Dichlorodifluoromethane (R12) / 75-71-8 | P | S | 2.2 | |||||
| Dichlorofluoromethane (R21) / 75-43-4 | P | S | 2.2 | |||||
| Dichlorosilane / 4109-96-0 | S | P | S | 5 | 2.3, 2.1, 8 | |||
| 1,2 –Dichlorotetrafluoroethane(R114a) / 76-14-2 | P | S | 2.2 | |||||
| Diethylamine / 109-89-7 | P | 3, 8 | ||||||
| Dimethylamine / 124-40-3 | P | S | S | 2.1 | ||||
| Disilane / 1590-87-0 | P | 5 | 2.1 | |||||
| Ethane / 74-84-0 | P | S | S | 2.1 | ||||
| Ethylene / 74-85-1 | P | S | S | 6 | 2.1 | |||
| Ethylene Oxide / 75-21-8 | P | P | S | 7 | 2.3, 2.1 | |||
| Fluorine / 7782-41-4 | P | P | 2.3, 5.1, 8 | |||||
| Germane / 7782-65-2 | S | P | 6 | 2.3, 2.1 | ||||
| Helium / 7440-59-7 | P | 2.2 | ||||||
| Helium (Liquid) / 7440-59-7 | P | S | 2.2 | |||||
| Hydrogen / 1333-74-0 | P | S | 2.1 | |||||
| Hydrogen (Liquid) / 1333-74-0 | P | S | S | 2.1 | ||||
| Hydrogen Bromide / 10035-10-6 | P | S | 2.3, 8 | |||||
| Hydrogen Chloride/ 7647-01-0 | P | S | 2.3, 8 | |||||
| Hydrogen Cyanide / 74-90-8 | S | P | 6.1, 3 | |||||
| Hydrogen Sulfide / 7783-06-4 | S | P | S | 2.3, 2.1 | ||||
| Isobutane / 72-28-5 | P | S | S | 2.1 | ||||
| Krypton / 7439-90-9 | P | 2.2 | ||||||
| Liquefied Petroleum Gas (LPG) / 68476-85-7 | P | S | S | 2.1 | ||||
| Methane / 74-82-8 | P | S | 2.1 | |||||
| Natural Gas / NA | P | S | 2.1 | |||||
| Neon / 7440-01-9 | P | 2.2 | ||||||
| Neon (Liquid) / 7440-01-9 | P | S | 2.2 | |||||
| Nickel Carbonyl / 13463-39-3 | S | P | 8 | 6.1, 3 | ||||
| Nitric Oxide / 10102-43-9 | S | P | 2.3 | |||||
| Nitrogen / 7727-37-9 | P | 2.2 | ||||||
| Nitrogen (Liquid) / 7727-37-9 | P | S | 2.2 | |||||
| Nitrogen Dioxide / 10102-44-0 | P | P | S | 2.3, 5.1, 8 | ||||
| Nitrous Oxide / 10024-97-2 | P | S | 2.2, 5.1 | |||||
| Oxygen / 7782-44-7 | P | 2.2, 5.1 | ||||||
| Oxygen (Liquid) / 7782-44-7 | P | S | 2.2, 5.1 | |||||
| Ozone / 10028-15-6 | P | P | 2.2 | |||||
| Pentaborane / 19624-22-7 | S | P | 5 | 4.2, 6.1 | ||||
| Phosgene / 75-44-5 | P | S | 2.3, 8, 4.2 | |||||
| Phosphine / 7803-51-2 | S | P | 2.3, 2.1 | |||||
| Propane / 74-98-6 | P | S | S | 2.1 | ||||
| Propylene Oxide / 75-56-9 | P | S | 9 | 3 | ||||
| Silane / 7803-62-5 | P | 5 | 2.1 | |||||
| Sulfur Dioxide / 7446-09-5 | P | S | S | 2.3, 8 | ||||
| 1,1,1,2- Tetrachlorodifluoroethane(R112a) / 76-11-9 | P | 2.2 | ||||||
| 1,1,2,2- Tetrachlorodifluoroethane(R112) / 76-12-0 | P | 2.2 | ||||||
| Tetrafluorohydrazine / 10036-47-2 | P | P | 10 | 1.1 | ||||
| Xenon / 7440-63-3 | P | 2.2 | ||||||
1From: Compressed Gas Association P-1 2000.
*Other Codes:
- May decompose violently in its free state under pressure in excess of 15 psig.
- Decomposes or reacts violently upon contact with water.
- Shipped with an inhibitor to avoid polymerization.
- Generally shipped pressurized with a diluent gas.
- Pyrophoric.
- May undergo explosive decomposition at elevated pressures when heated or ignited.
- Explosive decomposition on prolonged storage or hazardous polymerization may occur if contaminated.
- Thermally unstable; decompose violently at 140°F.
- Reaction with water may lead to a runaway reaction.
- Unstable in air for more than a few minutes.
2From: Department of Transportation Hazardous Materials Table 49 CFR 172.101:
- Class 1.1 = Explosive
- Class 2.1 = Flammable Gas
- Class 2.2 = Non-flammable, nonpoisonous compressed gas – including compressed gas, liquefied gas, pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing gas
- Class 2.3 = Gas poisonous by inhalation
- Class 5.1 = Oxidizer
- Class 8 = Corrosive Liquid
Flammable Gases #
Any gas for which flammable limits in air are reported is considered flammable. However, if the gas were also toxic, then toxic would be the primary hazard with flammable noted as secondary.
When using, handling, or storing a compressed gas that lists its primary and secondary hazard as flammable, incorporate the following controls into your standard operating procedures for using, handling, and storing compressed gases.
| CONTROL | DESCRIPTION |
| Engineering Controls: All Quantities | All lines and equipment associated with flammable gas systems must be grounded and bonded.Flash arrestors are designed to prevent a flash-back, should it occur, in a line containing a flammable gas.Portable fire extinguisher must available in the area where compressed gases and cylinders are used and stored.Use spark- proof tools when working with flammable gas.Do not use vessels, piping, or other materials that contain a significant amount of copper (usually considered to be more than 50% copper) with cylinders containing acetylene. |
| Engineering Control: Above the U-M MAQ | Flammable gas quantities above the U-M MAQ may be required to have the following engineering controls:The workspace is equipped with a continuous gas detection system.The gas detection system must initiate a local alarm that is both visible and audible.The gas detection system must transmit a signal to a constantly attended control station.Activation of the gas detection system must automatically shut off the flow of gas related to the system being monitored.The gas detection system must detect the presence of gas at or below the Lower Explosive Limit (LEL). If the gas is also toxic, the system should detect the presence of gas at or below the OSHA permissible exposure level or ceiling limit of the gas in lieu of the LEL.Emergency power must be provided for the exhaust ventilation, gas detection system, and alarm systems when required.Sprinkler protection for gas cabinets and other protective features may be required.NOTE: This information is for general guidance. Consult with your EHS representative to determine requirements for your particular usage. A code analysis may also be required. |
| Administrative Controls | Do not use acetylene at an operating pressure over 15 psig.Do not leave flow experiments using flammable gases unattended. |
Oxidizing Gases #
Oxidizing gases that, in the presence of an ignition source and a fuel, support and may vigorously accelerate combustion. If the gas was also toxic, this would be listed as primary hazard with oxidizer as the secondary hazard. Some gases, such as fluorine, are as aggressive an oxidizer as they are toxic, so both hazards are listed as primary.
When using, handling, or storing oxidizing gases, incorporate the following controls into your standard operating procedures for using, handling, and storing compressed gases.
| CONTROL | DESCRIPTION |
| Administrative Control | All equipment used for oxidizing gases must be cleaned with oxygen-compatible materials free from oils, greases, and other contaminants.Do not use oily hands or gloves when handling cylinders. The reaction between oxygen and hydrocarbons can be violent, even when small quantities are involved. |
Pyrophoric Gases #
When using, handling, or storing a compressed gas that is pyrophoric, incorporate the following controls into your standard operating procedures for using, handling, and storing compressed gases.
NOTE: This information is for general guidance. Consult with your EHS representative to determine requirements for your particular usage. A code analysis may also be required.
| CONTROL | DESCRIPTION |
| Engineering Control: Lecture Bottles | Lecture bottles of Pyrophoric gases that are located workspaces must be kept in a continuously mechanically exhausted ventilated hood or other continuously mechanically exhausted ventilated enclosure: |
| Engineering Controls: Cylinders Greater than Lecture Bottle Size | Cylinders of pyrophoric gases (greater than lecture bottle size) must be kept in approved continuously mechanically ventilated, sprinklered gas cabinets and must be equipped with an excess flow control device. |
| Engineering Control: Above the U-M MAQ | In addition to the requirements listed above, any quantity of Pyrophoric Gas above the U-M MAQ may be also required to have the following engineering controls upon consultation with your EHS representative:The workspace must be equipped with a continuous gas detection system.The gas detection system must initiate a local alarm that is both visible and audible.The gas detection system must transmit a signal to a constantly attended control station.Activation of the gas detection system must automatically shut off the flow of gas related to the system being monitored.The gas detection system must detect the presence of gas at or below the Lower Explosive Limit (LEL). If the gas is also toxic, the system must detect the presence of gas at or below the OSHA permissible exposure level or ceiling limit of the gas in lieu of the LEL.Emergency power must be provided for the exhaust ventilation, gas detection system, and alarm systems when required. |
Toxic, Highly Toxic, and Corrosive Gases #
In all cases, if a gas is toxic, this is the primary hazard. A toxic gas is any gas that has an LC50 less than or equal to 2,000 ppm but greater than 200 ppm. A highly toxic gas is any gas that has a LC50 in air of 200 ppm or less. Requirements laid out in this section shall also apply to cylinders of carbon monoxide.
Primarily, most gases in the absence of water are not corrosive. However, because most sources refer to the gas properties in moist air, corrosive is listed as a mostly secondary hazard where appropriate.
Corrosive gases can chemically destroy exposed body tissue; therefore, avoid contact to skin and eyes.
When using, handling, or storing a compressed gas that lists its secondary hazards as corrosive, incorporate the following controls into your standard operating procedures for using, handling, and storing compressed gases.
When using, handling, or storing a compressed gas that is toxic, incorporate the following controls into your standard operating procedures for using, handling, and storing compressed gases.
NOTE: This information in the table is for general guidance. Consult with your EHS representative to determine requirements for your particular usage. A code analysis may also be required.
| CONTROL | DESCRIPTION |
| Engineering Control | Install an emergency shower and eyewash within 25 feet where corrosive materials are used.NOTE: This engineering control is required. |
| Engineering Control: Lecture Bottles | Lecture bottles of toxic gas, highly toxic gas, or carbon monoxide and are located in workspaces must be kept in a continuously mechanically exhausted ventilated hood or other continuously mechanically exhausted ventilated enclosure. |
| Engineering Controls: Below the U-M MAQ | Departments using or storing toxic gas, highly toxic gas, or carbon monoxide cylinders (greater than lecture bottle size) in the workspace must comply with the following requirements as a minimum:Cylinders must be kept in approved continuously mechanically ventilated gas cabinets.The workspace must be equipped with a continuous gas detection system. NOTE: Gas detection may not be required where the physiological warning properties for the gas are at a level below the accepted permissible exposure level or ceiling limit of the gas.The gas detection system shall initiate a local alarm that is both visible and audible. |
| Engineering Controls: Above the U-M MAQ | Departments using a toxic gas, highly toxic gas, or carbon monoxide in quantities above the U-M MAQ in any size cylinder may be required to have the following engineering controls upon consultation with an EHS representative:An approved continuously mechanically ventilated gas cabinet to store the cylinders.A continuous gas detection system in the work place that meets the following requirements: NOTE: Gas detection may not be required where the physiological warning properties for the gas are at a level below the accepted permissible exposure level or ceiling limit of the gas.It must initiate a local alarm that is both visible and audible.It must transmit a signal to a constantly attended control station.Activation of the gas detection system must automatically shut off the flow of gas related to the system being monitored.It must detect the presence of gas at or below the OSHA permissible exposure level or ceiling limit of the gas.Emergency power for the exhaust ventilation, gas detection system, and alarm systems when required.Treatment systems for the exhaust.Sprinkler protection for gas cabinets and other protective features. |
| Administrative Controls | Check equipment and lines frequently for leaks. Metals become brittle when used in corrosive gas service. |
| PPE | Wear safety goggles, lab coat, and gloves as indicated by your workspace SOP. |
Emergency Plan #
EHS recommends that an emergency plan is written if the compressed gas used requires a continuously exhausted gas cabinet or enclosure or a gas detection system, alarm, etc.
20.14 Cryogenic Gases and Liquids / Liquefied Gases #
Types of Cryogenic Liquids #
Each cryogenic liquid has its own specific properties, but most can be placed into one of three groups:
- Inert Gases: Inert gases in general are chemically non-reactive. They do not burn or support combustion. Examples of this group are nitrogen, helium, neon, argon, and krypton.
- Flammable Gases: Some cryogenic gases produce a gas that can burn in air. The most common examples are hydrogen, methane, and liquefied natural gas.
- Oxygen: Many materials considered as non-combustible can burn in the presence of liquid oxygen. Organic materials can react explosively with liquid oxygen. The hazards and handling precautions of liquid oxygen must therefore be considered from other cryogenic liquids.
Applications #
Cryogenic Liquids have many applications including freezing and storing biological specimens, experimental applications, and superconducting electromagnets for particle acceleration.
Potential Hazards #
The primary hazards associated with cryogenic liquids are: frostbite/cryogenic burns/hypothermia, asphyxiation, fire/explosion, sudden release of pressure, and structural embrittlement.
- Frostbite/Cryogenic Burns: Cryogenic liquids and their associated cold vapors and gases can produce effects on the skin similar to a thermal burn. Brief exposures that would not affect skin on the face or hands can damage delicate tissues such as the eyes. Prolonged exposure of the skin or contact with cold surfaces can cause frostbite. Unprotected skin can stick to metal that is cooled by cryogenic liquids. The skin can then tear when pulled away.
- Asphyxiation: Cryogenic liquids have large liquid-to-gas expansion ratios and in confined or poorly ventilated areas the expanding gases will displace oxygen, presenting an asphyxiation hazard to personnel working in the area.
- Fire/Explosion: Oxygen has a higher boiling point (-183°C) than cryogenic liquids such as nitrogen (-195°C), hydrogen (-252.7°C), and helium (-269°C). As a result of this disparity, oxygen can be inadvertently condensed out of the atmosphere during the use of these lower-boiling cryogenic liquids, resulting in the creation of a highly hazardous oxygen enriched atmosphere that can greatly increase the risk of fire or explosion. Additionally, if a cryogenic liquid is subjected to a large amount of heat input, a flash vaporization can occur, resulting in a boiling liquid expanding vapor explosion (BLEVE). Liquid oxygen condensation in vacuum traps or from ice plug formation or lack of functioning vent valves in storage Dewars can also pose a serious explosion hazard.
- Sudden Release of Pressure: Sealed containers or closed off piping systems that contain cryogenic liquids can rupture when the cryogenic liquids are allowed to warm to room temperature. The rupture results as the warming cryogenic liquids change to the gas state and expand, producing enormous pressure within the container or piping system.
- Structural Embrittlement: Materials that are normally structurally sound, such as carbon steel, zinc, plastic, and rubber, can become brittle and fail due to thermal stress fracturing when subjected to cryogenic temperatures.
Injury #
Personnel should be aware of the hazards associated with handling and usage of cryogens. If a lab worker is injured, the person should seek immediate medical attention (Occupational Health Services or University Hospital Emergency Department). Their supervisor must complete a Work Connections Injury or Illness Report.
Personal Protective Equipment #
The extreme cold and unique properties of cryogenic liquids make strict observance of the use of proper personal protective equipment (PPE) an absolute necessity. Failure to use proper PPE while working with cryogens will result in severe injury or death.
- Eye/Face Protection: Safety Glasses and a face shield must be worn while dispensing cryogenic liquids. Never wear contact lenses while working with cryogenic liquids.
- Hand Protection: Hands must be protected with cryogenic gloves that fit loose enough to be quickly removed in case the liquid becomes entrapped close to the skin.
- Lab Coats/Aprons: A lab coat that can be easily removed must be worn over a long sleeve shirt and long pants without cuffs. The use of an apron made of non-woven material, such as leather, is also strongly recommended as a secondary form of protection when working with any more than just a few milliliters of cryogenic liquid. Short sleeved shirts and shorts offer no protection and must not be worn.
- Foot Protection: Closed toed leather or safety shoes that are impervious to liquid spills must be worn. Sandals or sneakers/gym shoes offer no protection and must not be worn
Engineering Controls #
Cryogenic liquids must only be used in well-ventilated areas. Large laboratory spaces, designed to have 6-12 air changes per hour, are generally acceptable. Users of cryogenic liquids must always consider the size of the room, amount of cryogenic liquid they are using, and be mindful of the ability cryogens have to create an oxygen-deficient atmosphere. In some circumstances, an oxygen monitor may be needed as an additional engineering control.
Use of Cryogenic Liquids #
Cryogenic liquids have properties that make them more dangerous to use than other liquids: extremely cold temperatures, high liquid-to-vapor expansion ratios, and flammability for certain liquids. Contact with cryogenic liquids, cryogenic equipment, or splashing liquid can cause severe tissue damage. Burns, frostbite, tearing of the flesh, and eye damage are all possible injuries. Vapors from boiling liquids can also cause eye damage, frostbite to the skin, and oxygen deficient environments.
To minimize exposure during use implement the following procedures:
- Wear appropriate PPE as discussed in the PPE section.
- Do not wear jewelry or other materials that could trap liquid to the skin if spilled.
- Stay out of the vapor pathway.
- Ventilate the room in case of spill or leak.
- Use fume hoods when working with cryogens if possible.
- Always use tongs when handling objects in cryogenic liquid.
- Only use approved materials with cryogens. Unapproved materials (such as plastic, rubber, wrought iron, hollow tubes, and carbon steel) will become brittle and shatter or, in the case of hollow tubes, become over pressurized.
- Periodically inspect equipment and remove ice and frost blockages from openings to prevent over pressurization.
- Do not tamper with pressure relief valves. Report any leaks or improperly set relief valves to the manufacturer.
- Do not use corrosive cleaning materials that could damage the metal jacket.
Dispensing and Transport of Cryogenic Liquids #
Special precautions must be taken to prevent a spill while dispensing or transporting cryogens, in addition to minimizing exposures from liquids and vapors. The high liquid to vapor expansion ratio could rapidly displace all oxygen in a room and result in asphyxiation. Always wear proper PPE when dispensing or transferring cryogenic liquids.
Use no fewer than two personnel to transport cryogenic liquids in large Dewars and cryogenic liquid cylinders; use handcarts equipped with brakes.
Never transport cryogenic liquids on an elevator with live passengers. When transporting cryogenic liquids via elevator the sender should remain outside the elevator, push the button for the desired floor and let the doors close. Another person should be ready on the receiving floor to take the container off the elevator. All elevator doors from the starting floor to the floor of the final destination should be manned to prevent entry by anyone between floors.
Always use care when handling equipment. Damage to Dewars could result in the loss of vacuum in the jacket and increased evaporation.
When carrying a Dewar, wear PPE and hold it as far away from the face as possible. Containers that cannot be easily and safely carried should be placed on a stable wheeled base designed for the Dewar.
When obtaining liquid from a large dispensing Dewar or cryogenic liquid cylinder, cool the secondary container by adding a little cryogenic liquid first. Then dispense slowly to mitigate thermal stress.
Stay in constant attendance of the filling operation and do not overfill. Also, do not allow the cryogenic liquid to fall through a distance to reach the receiving vessel.
When manually pouring liquid into a smaller dewar, ensure the secondary container is secured. Pour slowly to prevent excess splashing and do not overfill. Use a phase separator, if available, to control the vapor path while pouring.
Storage of Cryogenic Liquids #
Storage of cryogenic liquid cylinders or Dewars in hallways, unventilated closets, environmental rooms, and stairwells is prohibited. A cryogenic liquid storage unit left open to the atmosphere, or catastrophic failure of a storage unit, could create an oxygen deficient atmosphere. Follow these procedures to reduce the likelihood of this occurrence:
Store Dewars in well-ventilated rooms with a minimum of six air changes per hour. Bulk cryogenic liquid dispensing areas within buildings must also be well-ventilated. EHS recommends continuous oxygen monitoring equipment in bulk dispensing areas and may recommend detection systems and alarms for storage areas depending on location, quantity of material stored and ventilation rate. If the ventilation rate is unknown, contact EHS for an evaluation.
Dewars and cryogenic liquid cylinders should be placed so that vents and openings are oriented away from personnel and lab equipment.
Do not store cryogenic liquids with corrosive or flammable chemicals.
No more than one backup Dewar or cryogenic liquid cylinder is allowed per piece of equipment. Additional Dewars or cryogenic liquid cylinders must be stored in areas designed for such storage. Contact EHS at 647-1143 to evaluate potential storage locations.
Glass Dewars must have an exterior coating/cover to minimize projectiles in the event of an explosion. Newer Dewars may have a plastic mesh over the exterior for this purpose. Older Dewars must be thoroughly taped or replaced.
Special Precautions for Flammable Cryogenic Liquids and Liquid Oxygen #
Flammable cryogenic liquids like methane, hydrogen, and liquefied natural gas introduce an additional hazard. Oxygen does not burn, but accelerates and supports combustion. High concentration oxygen atmospheres substantially increase combustion rates of other materials and may form explosive mixtures with other combustibles. Contact EHS at 647-1143 to assess engineering and work practice controls if you plan to work with these materials.
There are several industry guidelines that refer to flammable liquids that should be considered in addition to these recommendations.
All combustible materials should be kept away from flammable liquids and oxygen. There should be “No Smoking” signs posted, and no sources of ignition should be present in this area.
Oxygen Dewars and equipment should be kept very clean and dry. Surface contamination could become ignited if oxygen leaks from the Dewar and provides a local oxygen enriched area.
Stationary equipment should be properly grounded and mobile equipment should be properly bonded when dispensing.
Valve operation should occur very slowly to prevent ignition of contaminants in the system.
Hydrogen venting should be independent from other ventilation systems and may require a nitrogen purge capability.
Emergency Procedures #
Liquid Nitrogen (LN2) is the most commonly used cryogenic liquid. Oxygen depletion resulting from nitrogen gas may occur rapidly with no warning properties. A person entering an oxygen deficient environment may become disoriented and unable to respond properly.
Nitrogen gas is odorless, colorless, tasteless, and inert. The failure of a large cryogenic liquid cylinder could spill 180 L of LN2; in gas form this will completely displace all oxygen in a 21 x 21 x 10 ft. room. A much smaller spill in the same room could still create a safety hazard. Simply reducing the oxygen content in a room below 19.5% is considered an oxygen deficient environment.
Implement the following procedures to minimize the risk of asphyxiation:
Periodic equipment inspections, removal of ice blockages, and replacement of damaged or old storage units will reduce the probability of the catastrophic failure of a storage unit. Ice blockages that prevent the container from venting properly can cause an explosion hazard. Contact DPSS at 911 if ice blockages are observed.
If a spill occurs immediately exit the area. With adequate ventilation it may be appropriate to return to the area after thirty minutes. Contact EHS to monitor oxygen levels in the area and determine when it is safe to re-enter.
If experiencing symptoms such as lightheadedness, dizziness, or confusion, immediately seek fresh air and receive medical attention.
If an employee becomes unconscious in a cryogenic liquid storage area they should only be retrieved by personnel using proper PPE (such as a Self Contained Breathing Apparatus). DPSS should be immediately notified at 911 (if calling from a cell phone must notify dispatch that you are calling from U of M campus) to coordinate emergency rescue services. Over fifty percent of deaths associated with asphyxiation in confined spaces occur to would-be rescuers.
Once personnel have been removed to fresh air, provide rescue breathing or CPR until paramedics arrive.
In the event of contact with cryogenic gases or liquid, immediately remove any clothing that has been contaminated. In the event of clothing contamination with oxygen, hydrogen, or carbon monoxide, it is important to remove clothing, evacuate personnel from the facility, and keep away from ignition sources.
Flush or soak the area with warm water (no greater than 105°F).
Do not apply dry heat or rub damaged flesh or eyes.
Employees should notify their supervisor of injuries and report to Occupational Health Services or University Hospital Emergency Department for medical evaluation and follow-up. The supervisor must complete the Work Connections Injury and Illness form to report the incident
Technical Support #
All referenced guidelines, regulations, and other documents are available through EHS (734-647-1143).
