Physical Hazards

Basic safety issues relative to the “physical hazards” noted below are presented here. Obviously, each of these areas can be much more technically complex than noted here and the safety issues can vary greatly depending on the specific piece of equipment, or application. The physical hazard of ionizing and non-ionizing radiation are covered in other parts of the UCSB EH&S website.

Contents:

Cryogens
Compressed Gas Cylinders and Other Pressure Systems
Vacuum Systems
Electrical Systems

i. Cryogens

Examples: Liquid oxygen, liquid nitrogen, liquid helium, dry ice

Cryogens present a variety of serious hazards which include: low temperature burns, over pressurization explosions, toxicity, fire, implosions, material failures and asphyxiation. Cryogenic solids and liquids create extremely large volumes of gas upon vaporization.

Hazard Properties

• These materials are extremely cold (-100 deg. C to –270 deg. C) and, upon contact, can instantly freeze other materials. Serious tissue damage may occur upon exposure to low temperatures. Contact with cryogens may cause living tissue to freeze and become brittle enough to shatter.

• Cryogenic liquids and gases have many properties and hazards in common with compressed gases, and must be handled with similar caution.

• Be aware of ice that can plug or disable pressure-relief devices. Ensure adequate pressure-relief mechanisms are functional, i.e., never use tight-fitting stoppers or closures without pressure-relief devices.

Practices

• Know and understand the cryogenic system and emergency procedures (shut- off valves, alarm systems, monitors, exits, fire extinguishers, safety showers and eyewashes).

• Do not move an over-pressurized container. Evacuate and seal area, call for appropriate assistance

• Avoid trapping cryogenic liquids between closed sections.

•Dewar flasks or other glassware devices should be taped on the outside or provided with shatterproof protection to minimize flying glass particles in case of implosion. Dewar flasks should be vented with a bored or notched stopper.

• Cool cryogenic containers slowly to reduce thermal shock, flashing, and loss of material.

• Store and use only in an adequately ventilated area. Proper ventilation will help prevent explosions and fires in the cases of liquid oxygen, air, and hydrogen and will prevent asphyxiation in the cases of dry ice, nitrogen, and helium. But the large volumes generated by any liquefied gas makes ventilation an important priority.

• Persons who handle cryogens should be protected by: a face shield or safety goggles, lab coat or apron; gloves or mitts which can be shaken off quickly if cryogenic material gets into the glove; long sleeves and cuffless pants hanging over the tops of the shoes are also recommended.

• Use only appropriate low-temperature compatible materials and storage vessels.

• When utilizing cold baths with solvents, use in a hood with a catch pan. Be aware of increased fire hazard. Be prepared for vigorous solvent boiling upon initial addition of solvent.

• Avoid condensing oxygen or contact with organic material when using liquid nitrogen. Flush cold traps with nitrogen to avoid condensation of oxygen from air within the trap. Condensed oxygen when contacted with organic materials can cause a powerful explosion.

• If there is any change in the water-white color of the liquid nitrogen, discard it. Condensed liquid oxygen is blue in color.

• Do not use stainless steel with liquid oxygen (it burns).

ii. Compressed Gas Cylinders and Other Pressure Systems

COMPRESSED GAS CYLINDERS

Compressed gas cylinders must be handled very carefully by trained individuals. The diffusive nature of gas can result in serious hazards over very large areas. Compressed gas cylinders can be hazardous because 1) if they are mishandled, they can become “unguided missiles” with enough explosive force to go through concrete walls due to the high pressure inside the tank. 2) they often contain materials which are inherently toxic or highly flammable. For these reasons, particular care must be exercised with compressed gases. Anyone who handles or uses a cylinder shall follow the rules described on the following page:

Toxic and flammable gases have stringent and specific requirements for use and storage. UCSB has developed a Campus Toxic Gas Program, which all new installations must prior to use. Many of the campus labs using these gases have been and will be retrofitted to comply with current Fire Code regulations. Examples of some of the more common lab gases which fall under the provisions of this program include: fluorine, ammonia, diborane, ethylene oxide, nitric oxide, nickel carbonyl, phosgene and silane. Call the EH&S Lab Safety Specialist at x4899 for additional details.

Transport

• To transport or move a cylinder, strap it to a handtruck in an upright position.

• Make sure the valve protection cap and outlet plug are in place. Leave the valve protection cap on at all times, unless the cylinder is in use.

• Do not move a cylinder by rolling, dragging or walking it across the floor. Never leave a cylinder free-standing.

Storage

• All cylinders (empty or full) must be secured upright with chains and brackets bolted to a solid structural member. Chains should be 3/16 inch welded link or equivalent. At least one chain must be used to secure each cylinder at a point two-thirds up the cylinders height. C-clamp bench attachments and fiber/web straps are not acceptable because they are not seismically sound. Any variations of these requirements must be approved by EH&S. (Campus Policy 5445)

• Keep cylinders away from heat and sources of ignition. Do not place cylinder where contact with any electrical circuit can occur.

• Protect cylinders from weather extremes, dampness and direct sunlight.

• Inspect cylinders and delivery equipment routinely for signs of wear, corrosion, or damage. Replace equipment as necessary.

• All cylinders must be clearly labeled as to their contents — do not use unlabeled cylinders and do not rely on color coding for identification.

• Understand that “Empty” implies “end of service” and as such, the cylinder may still have greater than 25 psig of pressure remaining.

Leaks

• If the material in the tank is toxic or flammable and you can not stop the leak, get everyone out of the area and report it to EH&S at x3194 and Dispatch at 9-911.
Use

• New construction of gas delivery systems involving toxic gases must be authorized by EH&S prior to installation and operation.

• Wear appropriate protective equipment (safety glasses or face shield) when using or transporting compressed gas cylinders.

• Use regulators designed for a specific gas. (Consult your gas vendor or catalog for proper regulator compressed gas association (CGA) number (on nut) for use with corresponding compressed gas cylinder. Do not use any adapter between cylinders and regulators.

• Post signs in laboratory area when using corrosive, toxic or flammable gases. The door placard system maintained by EH&S on the campus may be used for this purpose.

• Know emergency procedures. Install emergency shut-off valves wherever necessary.

• Never modify, tamper, force or lubricate safety devices, cylinder valve or regulator.

• Do not allow grease or oil to come into contact with oxygen cylinder valves, regulators, gauges or fittings. An explosion or fire can result. Oxygen cylinders and apparatus must be handled with clean hands and tools. Remember that oxygen supports and greatly accelerates combustion.

• Never force a gas cylinder valve — if it cannot be opened by the wheel or small wrench provided, the cylinder should be returned.

• When opening cylinder valve, do not hold regulator. Stand with valve between you and regulator. Open cylinder valves slowly, directed away from your face.

• Release a compressed gas gently to avoid build-up of static charge which could ignite a combustible gas.

• Special precautions are necessary for acetylene usage. Acetylene cylinders contain a solvent in which the gas is dissolved and therefore the cylinder must be kept upright. Note that acetylene can form explosive compounds in contact with copper or brass. Consult the vendor or manufacturer for proper operating equipment and procedures.

• Do not leave a regulator under pressure and shut main cylinder valve when in use.

• Do not extinguish a flame involving a highly combustible gas until source of gas has been shut off. Re-ignition can cause an explosion.

Disposal

• Empty cylinders should be labeled “EMPTY” or “MT”, and returned to the supplier or held in the department with other empties for pickup.

• Always leave at least 25 psi minimum pressure in all “EMPTY” cylinders to prevent contamination and the formation of explosive mixtures.

• Return damaged or corroded cylinders and cylinders with a test date more than five years old stamped on the shoulder to the vendor. Some gas cylinders should be disposed or returned at shorter intervals (e.g., corrosives should be disposed or returned every six months).

OTHER PRESSURE SYSTEMS

Pressurized Vessels and Chambers––

Pressurized vessels and chambers have a wide variety of hazards associated with their operation. The systems are typically complicated and require extensive training prior to use. Developing thorough knowledge of a system via instruction and close supervision is highly recommended.

• The vessel and all components must be properly selected for the process parameters, including:

• Material Selection: physical and chemical properties at operating conditions

• Design:
- Factor of safety
- Design pressure and temperature
- Maximum allowable working pressure
- Loading
- Hydrostatic and pneumatic testing

• Always operate vessel within design specifications. Never use a vessel if specifications are unknown or if there is any indication vessel has been damaged or degraded. Many commercial vessels are ASME Code stamped (or rated) for a particular use.

• All pressurized vessels must have a pressure relief valve or other safety device to prevent catastrophic failure of the vessel. The relief valve should be tested regularly. When hazardous vapors are involved, make sure the safety relief mechanisms are properly vented.

• The chamber or vessel must be inspected regularly. If feasible, dimensional inspections should be performed periodically during service to check for plastic deformation. Pay particular attention to high-pressure fittings and seals.

• Accurate records of use must be maintained. Most vessels have a specified “service life” or number of cycles permitted between inspections or replacement of components.

• Prepare for power outages whether you are present or not. Some valves close upon loss of power, some open. Understand the effects that a series of valve openings and closings will have upon the system's safety and integrity.

• Follow manufacturer's instructions when operating so as to avoid injury and/or damage to equipment and area.

iii. Vacuum Systems

Vacuum systems have a wide variety of hazards associated with their operation. There are risks associated with both implosion and explosion, as well as the release of toxic gases and materials. The systems are typically complicated and require extensive training prior to use. Developing thorough knowledge of a system via instruction and close supervision is highly recommended.

General Safety

• Construction and materials able to withstand 2.5 times the maximum allowable working pressure should be used.

• Be thoroughly familiar with emergency procedures in the event of an accident. These procedures need to be an integral part of the operation of any vacuum system.

• Prepare for power outages whether you are present or not. Some valves close upon loss of power, some open. Understand the effects that a series of valve openings and closings will have upon the system's integrity.

• Understand the type of vacuum pumps being used and their limitations. Always check with the manufacturer for the appropriate application.

• When changing belts on a mechanical pump, make sure the power cord is unplugged to prevent accidental startup of the pump.

• Be aware of the hot surface in oil diffusion pumps and protect nearby areas from exposure.

Pressure

• Vacuum systems which manipulate hazardous materials should be located in ventilated hoods.

• Similar precautions should be employed in all vacuum distillations in which a water pump is used because sudden loss of pressure will force water backup into the apparatus being evacuated. A Bunsen valve in the trap will avoid much of this difficulty.

• Systems must have adequate safety relief mechanisms to avoid over- pressurization. When hazardous vapors may be involved, make sure the safety relief mechanisms are properly vented.

Traps

• System must have appropriate traps to prevent chemical, radioactive or biohazardous material from contaminating the vacuum or house lines.

• Operation of low temperature gas or oil traps must be thoroughly understood. Both the cooling and warming phases deserve undivided attention. For example, the condensation of oxygen from air due to an open valve may cause a serious explosion.

Chemical Hazards

• Cryo pumps may be used to pump gases which are non-reactive at low temperatures. Upon warming, in the case of pump regeneration or power outage, those same gases may react violently causing an explosion.

• Mechanical pump oil can become contaminated with hazardous materials or from chemical reactions. Upon maintenance, proper protective equipment must be employed. A safe, ventilated area should be used for changing pump oil as many harmful vapors may be released.

• Mechanical pump exhaust may require suitable treatment. Depending upon the application, this may involve a relatively simple filter, an exhaust manifold, or treatment system.

• Systems which involve the evaporation of materials often present risks associated with particles that can be inhaled. Understand the problems associated with such systems and the methods used to minimize exposure.

iv. Electrical Systems

The effects of electrical shock can range from slight tingling to almost instantaneous death. The current which induces injurious effects varies considerably depending on factors such as current, frequency, skin resistance, duration, voltage, exposure point in phase of heart cycle, and path of exposure. Currents as little as 0.5 mA have been found to be hazardous.

Injuries and death from electrical shock can result both from induced malfunction of the heart and lung muscles and from burns. Survival of a shock incident may still cause both immediate and long-term destruction of tissue, nerves, and muscle to heat generated by the current.

A significant number of fires are caused by either malfunctioning electrical equipment, equipment failure, or improper use. These fires are also responsible for loss of life, injury and significant loss of property.

The following are some do’s and don’ts for working with and around electricity.

• Avoid becoming part of the circuit (a current path through the heart can easily be fatal).

• Know main way to disconnect power to equipment. Clearly label switches and lines.

• With high voltages assume floor is a conductive ground.

• Never work on live circuits, use a single hand whenever possible and no jewelry or watches.

• Know rescue procedures:

— Shut off power
— Remove/disengage victim using insulator (like a stick)
— Send for help
— Administer CPR if and only if you are trained to do so
— Keep the victim warm, comfortable, lying down, until help arrives. Do not give the victim anything to eat or drink until consultation with physician.

• Utilize the correct switches, relays, connectors, wires and other components to prevent overheating. Use the correct fuses and breakers -- check rating.

• Understand the proper application of capacitors and inductors (they can cause massive power surges and arcing).

• Do not operate electrical devices in explosive atmospheres unless they are rated as “intrinsically safe” for that purpose

• Insulation must be adequate for the voltage and current (inspect frequently for thinning, cracking, and environment deterioration).

• Properly ground all equipment and instruments

The following safety devices and controls should be used to reduce the dangers of electrical hazards if appropriate for the application:

• Fault-current-limiting devices (fuses, resistors, circuit breakers)

• Enclosures or barriers that protect against accidental electrical contact (and exploding capacitors)

• Insulation

• Grounding and shorting devices

• Interlocks

• Lockout devices and procedures ( a means to ensure that the power cannot be activated without the user’s explicit knowledge)

• Power shutoff switches conspicuously placed with warning devices such as buzzers of lights that indicate an energized power supply

• Instrumentation and control systems that provide operator information on equipment functioning status.

• Routine inspection and maintenance

Where to get information on electrical safety issues?

— Consult with qualified persons. At UCSB, qualified personnel can be found in departmental electronics shops or Facilities Management, Electric Shop.
— National Electrical Safety Electrical Code, ANSI C2, American National Standards Institute, NY.
— CRC Handbook of Laboratory Safety, 4th ed., (A. Keith Furr, ed.), CRC Press (1995).
— Prudent Practices in the Laboratory, National Academy Press, (1995).