Dangerous Gas Policy


Dangerous Gas Policy


The purpose of this policy is to establish minimum standards for lab researchers that utilize dangerous gases. These standards will reduce the likelihood of a dangerous gas release and ensure the safety of laboratory researchers, building occupants and emergency responders.


Dangerous gases include any gases that may cause significant acute health effects at low concentration. For purposes of this policy, “dangerous gases” means toxic, highly toxic and pyrophoric gases with any of the following specific characteristics:

  • National Fire Protection Association (NFPA) health hazard rating of 3 or 4;
  • NFPA health hazard rating of 2 with poor physiological warning properties;
  • Extremely low occupational exposure limits in the absence of an NFPA health rating; or
  • Pyrophoric (self-igniting) characteristics.

Pyrophoric, toxic and highly toxic gases can be further defined:

  • Pyrophoric: Gas that, upon contact with air or oxygen, will ignite spontaneously at or below a temperature of 54.4 degrees C (130 degrees F).
  • Toxic: Gas with an LC50 in air of more than 200 parts per million (ppm), but not more than 2000 ppm by volume of gas or vapor, when administered by continuous inhalation for one hour (or less if death occurs within one hour) to albino rats weighing between 200 g and 300 g each.
  • Highly Toxic: Gas with an LC50 in air of 200 ppm by volume or less of gas or vapor when administered by continuous inhalation for one hour (or less if death occurs within one hour) to albino rats weighing between 200 g and 300 g each.

See Appendix 1 for a list of dangerous gases including NFPA health hazard rating and properties .


Principal Investigator

  • Maintain primary responsibility for dangerous gas safety in the laboratory.
  • Designate and address the use of dangerous gases as part of a standard operating procedure (SOP) that is included in the individual Laboratory Safety Plan.
  • Ensure the Chemical Inventory is updated with correct names and quantities of dangerous gases.
  • Provide training to laboratory personnel that utilize dangerous gases and document training.
  • Ensure that laboratory personnel are compliant in following the UNC Dangerous Gas Policy.
  • Ensure that gas monitors are calibrated and replace sensors based on manufacturer specifications. Records must be accessible to inspectors as part of lab safety documentation.
  • Notify adjacent labs of dangerous gas use and risks.

Laboratory Employees

  • Review and follow proper work practices as identified by the lab specific SOP and the UNC Dangerous Gas Policy.
  • Verify that dangerous gases are always used and stored in properly exhausted enclosures.

The Department of Environment, Health and Safety (EHS)

  • Implement the UNC Dangerous Gas Policy.
  • Review dangerous gas delivery system design prior to construction.
  • Review and provide feedback on dangerous gas SOPs as part of individual Laboratory Safety Plans.
  • Verify inventory amounts via the Chemical Inventory system.
  • Annually review and update the UNC Dangerous Gas Policy.
  • Train emergency responders (CHFD, UNC Public Safety) on dangerous gas locations and emergency response plans for dangerous gas lab spaces.
  • Respond to alarms related to dangerous gas systems.

Storage, Handling and Use Requirements

Lecture Bottles

All dangerous gas lecture bottles should be used and stored in a chemical fume hood or ventilated gas cabinet.


All dangerous gas cylinders should have a restricted flow orifice installed in the cylinder valve outlet that limits the maximum gas release rate during an accidental release.

All dangerous gas cylinders should be located within a ventilated gas cabinet or laboratory fume hood. Ventilated cabinets must meet the following requirements:

  • Located in a room or area which has independent exhaust ventilation;
  • Operate at negative pressure in relation to the surrounding area;
  • Have self-closing limited access parts or noncombustible windows to provide access to equipment controls, with an average face velocity of at least 200 feet per minute (fpm) and with a minimum of 150 fpm at any part of the access port or window;
  • Connected to an exhaust system;
  • Have self-closing doors and are constructed of at least 0.097 inch (12 gauge) steel;
  • Internally sprinklered;
  • Anchored; and
  • Contain no more than three (3) dangerous gas cylinders per gas cabinet.

Gas Detection System

A continuous gas detection system should be provided to detect the presence of gas at or below the permissible exposure limit (PEL) or ceiling limit. The detection system shall initiate a local visual and audible alarm and transmit a signal to a constantly attended location. Activation of the monitoring system shall automatically close the emergency shut-off valve on dangerous gas supply lines to the system being monitored. Gas monitoring sensor ports should be located inside the ventilated cabinet, near the equipment and in the lab operator area. Alarms will notify Public Safety, EHS and the Principal Investigator. An alarm status and gas concentration read out should be located outside the gas use room or be visible through a window.


All chemical fume hoods or gas cabinets must have a ventilation monitor that measures duct or enclosure exhaust performance. This monitor should be tied into an alarm to notify users if ventilation fails.

Emergency power should be provided for exhaust ventilation, gas detection systems, emergency alarm systems and temperature control systems. In the event of a power failure the detection system should continue to operate without interruption or gas systems should automatically shut down at the source.

An approved supervised smoke detection system must be provided in rooms or areas where dangerous gases are stored indoors.

Storage and use areas should be secured against unauthorized entry.

Only qualified personnel should perform dangerous gas cylinder change out. Each lab should have documentation of cylinder change out procedure as part of the SOP.

All empty dangerous gas cylinders should be labeled as “Empty” and be returned to vendor for disposal. If a vendor will not accept a cylinder or an older or compromised cylinder is found, contact EHS (919-962-5507) immediately for an assessment and to arrange disposal.

All users, lab occupants and emergency responders should be trained and know how to respond in the event of a dangerous gas leak.


Appendix 1

Dangerous Gases Table
Dangerous Gas (CAS#) NFPA Health Hazard Exposure Limits Corrosive or Pyrophoric Toxic (LC50>200 ppm but <2000 ppm) Highly Toxic (LC50<200 ppm)
Allene (463-49-0) 3        
Ammonia (7664-41-7) 3 35 ppm
Arsenic pentafluoride
4 5 mg/me
Arsine (7784-42-1) 4 3 ppm
    120 ppm
Boron trichloride
3 100 ppm
Boron trifluroide (7637-07-2) 3 3 ppm (C) CORROSIVE 417 ppm  
Bromine pentafluoride
3 0.1 ppm
CORROSIVE   50 ppm
Bromine trifluoride
4 5 ppm
CORROSIVE   50 ppm
1,3-butadiene (106-99-0) 4 10 ppm
Carbon tetrafluoride (75-73-0) 3        
Carbon monoxide (630-08-0) 2 35 ppm
Carbonyl fluoride (75-73-0) 3 5 ppm
  360 ppm  
Carbonyl sulfide (463-58-1) 3   CORROSIVE 1070 ppm  
Chlorine (7782-50-5) 3 1 ppm
CORROSIVE 293 ppm  
Chlorine trifluoride
4 0.1 ppm (C) CORROSIVE 229 ppm  
Cyanogens (460-19-5) 4 10 ppm
CORROSIVE 350 ppm  
Cyanogen chloride (506-77-4) 4 0.3 ppm
Diborane (19278-45-7) 4 0.1 ppm
Dichlorosilane (4109-96-0) 3   CORROSIVE 215 ppm  
Dimethylamine (124-40-3) 3 5 ppm
Fluorine (7782-41-4) 4 25 ppm
CORROSIVE   185 ppm
Germanium tetrahydride
(germane) (7782-65-2)
4 0.2 ppm
  442 ppm  
Hydrogen bromide (10035-10-6) 3 30 pp
Hydrogen chloride
3 50 ppm
Hydrogen cyanide (74-90-8) 4 50 ppm
    160 ppm
Hydrogen fluoride
3 30 ppm
CORROSIVE 1276 ppm  
Hydrogen selenide
3 1 ppm
Hydrogen sulfide (7783-06-4) 3 100 ppm (IDLH)   444 ppm  
Methyl bromide (74-83-9) 3 250 ppm (IDLH) CORROSIVE 302 ppm  
Methyl chloride (74-87-3) 2        
Methylsilane (992-94-9) 3        
Monomethylamine (74-89-5) 3     448 ppm  
Nickel carbonyl (13463-39-3) 4       35 ppm
Nitric oxide (10102-43-9) 3 100 ppm (IDLH)     131 ppm
Nitrogen dioxide (10102-44-0) 4 1 ppm (C) CORROSIVE   117 ppm
Nitrogen trifluoride
3 5 ppm (C) CORROSIVE 2000 ppm  
Phosgene (75-44-5) 4 2 ppm
    50 ppm
Phosphine (7803-51-2) 4 50 ppm
Phosphorous pentafluoride (7647-19-0) 3   CORROSIVE    
Phosphorous trichloride (7719-12-2) 3 0.5 ppm (STEL) CORROSIVE   104 ppm
Phosphorous trifluoride (7783-55-3) 3        
Silicon tetrahydride (silane) (7803-62-5) 2   PYROPHORIC    
Silicon tetrafluoride
Stibine (7803-52-3) 4 5 ppm
    100 ppm
Sulfur tetrafluoride
4   CORROSIVE   19 ppm
Sulfuryl fluoride (2699-79-8) 3 200 ppm (IDLH)   991 ppm  
Tungsten hexafluoride
3 3 mg/m3 (STEL) CORROSIVE   118 ppm
Vinyl chloride (75-01-4) 4 5 ppm (C)   390 ppm  

Contact Information

Policy Contact

Environment, Health and Safety
1120 Estes Drive
Campus Box #1650
Chapel Hill, NC 27599-1650
Phone: 919-962-5507

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Article ID: 131905
Thu 4/8/21 9:19 PM
Thu 5/5/22 4:24 PM
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Environment, Health and Safety
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