TOXIC GAS ORDINANCE
Use By All Unidocs Member Agencies or Where Approved By Your Local
Authority Cited: Toxic Gas Ordinance
A. Materials Regulated
- Nitrous oxide, silane, and sulfur hexafluoride are not regulated
by the Toxic Gas Ordinance (TGO). These materials are regulated,
however, pursuant to the California Fire Code and shall also be
subject to the requirements of the Santa Clara County Hazardous
Materials Subcommittee Guidelines.
- Hydrogen Fluoride shall be regulated as a Class II gas, based
on a current IDLH of 30 ppm.
- The TGO shall not apply to the registration and application
of pesticides since this is preempted by a provision of an Act
of Congress. Handling and storage of cylinders, however, shall
comply with all requirements of the TGO. (11/29/90)
- In the event that a revised IDLH is published which affects
the hazard classification of a material, individual jurisdictions
shall establish a new timetable for existing facilities to upgrade
their systems. (07/26/90)
- Substitute materials for toxic gases (e.g. Trimethyl Phosphite,
Tetraethylorthosilicate, etc.) shall be regulated by the TGO based
on toxicological data presented by a qualified third party.
- Mixtures of Regulated Materials: In the absence of an established
IDLH for a mixture containing a regulated material, the following
formula may be used:
A calculated LC50 for mixtures containing regulated materials
can be determined by using the following formula. The calculated
LC50 can then be used in the formula to calculate the Material
Hazard Index for the mixture.
LC50 of Gas Mixture (in ppm) = ______________________
(molar fraction of toxic component) / (ppm
LC50 of toxic component)
If more than one toxic component: LC50 (mixture)
= ________________ 1
where fi is the mole fraction of the ith toxic component
of the gas mixture and LC50i is the LC50
of the ith toxic component of the gas mixture. (03/02/94)
- Dilute toxic gas mixtures are regulated by the TGO. However,
when the concentrations are such that they are less than the standards
required by a specific control, the material may be exempted from
that particular control (e.g. concentrations less than PEL).
- Recent amendments to 49 CFR, Parts 171-180, [U.S. Department
of Transportation (DOT) regulations], expanded the definition
of toxic gases. The Poison-A classification was eliminated and
the definition expanded to conform to United Nations standards
on hazardous materials. Although this change greatly increased
the chemicals regulated as a poison gas by DOT, it was the intent
of the TGO to classify those gases listed as Poison-A materials
as Class I regulated materials. Therefore, the following materials
shall continue to be regulated pursuant to the TGO requirements
for Poison-A materials:
- Chloropicrin and methyl chloride mixture;
- Chloropicrin and nonflammable, nonliquefied compressed gas
- Cyanogen chloride containing less than 0.9% water;
- Cyanogen gas;
- Hexaethyl tetraphosphate and compressed gas mixture;
- Hydrocyanic acid (prussic) solution (5% or more hydrocyanic
- Hydrocyanic acid, liquefied;
- Hydrogen selenide;
- Insecticide, liquefied gas, containing Poison-A or Poison-B
- Nitric oxide;
- Nitrogen dioxide, liquid;
- Nitrogen peroxide, liquid;
- Nitrogen tetroxide, liquid;
- Organic phosphate, Organic phosphate compound, or Organic
phosphorus compound; mixed with compressed gas;
- Parathion and compressed gas mixture;
- Phosgene (diphosgene);
- Poisonous liquid or gas, n.o.s.;
- Tetraethyl pyrophosphate and compressed gas mixture.
- Halogenated, non-carbon-based gases may hydrolyze to their base
mineral acid upon contact with moisture. Therefore, the TGO requirements
(i.e. monitoring, treatment, compatibility, etc.) for these gases
shall apply to their decomposition products. (10/17/91)
(Example: Tungsten hexafluoride decomposes to hydrogen fluoride
(HF). Therefore, monitoring shall be required for HF at PEL,
treatment shall be required for HF to 1/2 IDLH, and piping materials
must be compatible with HF or secondary containment shall be
B. Material Hazard Index
NIOSH shall be used as the primary reference when determining the
Material Hazard Index (MHI). If no data is available from NIOSH,
then the EPA's published Level of Concern (LOC) may be used or "third
party" data shall be submitted. (07/12/90)
C. Piping and Controls
- Partial gas system upgrades shall require permits under the
same conditions as upgrades to existing underground fuel lines.
(06/21/90) For example:
- If a permit is required for a piping modification, then
upgrading of the entire system for that gas shall be required.
- If a permit is not required, such as for connecting an existing
piping system to a new piece of equipment, then upgrading
will not be required at this time.
- All primary piping for toxic gas systems shall pass a Helium
Leak Test of 10-9 cc/sec., where practical. Persons conducting
the tests shall possess a certificate of training. Individual
jurisdictions may require "third party" testing. (09/13/90)
- For the purpose of calculating the Maximum Threshold Quantity
(MTQ), storage tanks, cylinders and piping systems which can be
isolated in a manner approved by the Fire Chief may be designated
as separate storage vessels. (02/21/91)
D. Incompatible Materials
1) Compatibility of materials shall be determined by the National
Association of Corrosion Engineers (NACE). (06/21/90)
- The compliance proposal, due within 1 year of adoption of the
TGO, shall address each aspect of the project (i.e. identify dates
for submitting plans, obtaining funding, initiating upgrades,
completing upgrades, etc.).
- Special considerations may be given by the Fire Chief, in accordance
with the specific section of the local ordinance (if such a section
was provided) granting the Fire Chief this authority or with Section
2.301 of the California Fire Code (i.e. Vacuum distribution systems
for chlorine, ammonia, sulfur dioxide and silicon tetrachloride).
F. Seismic Protection
Automatic shut-down shall be required for the toxic gas sources
in the event of seismic activity at 0.3 G, or lower, as specified
by each individual jurisdiction. (11/08/90)
G. Gas Detection
- Monitoring systems shall be tested at the point of use. (06/21/90)
- The interval time for "continuous" gas detection shall be determined
by the Fire Chief in each jurisdiction. The maximum interval time
shall be 30 minutes, as defined by the UFC.
- Automatic shut-down shall occur upon gas detection at or below
PEL in occupied areas, and at or below 1/2 IDLH in unoccupied
- Continuous gas detection may not be required to detect the presence
of gas at or below the PEL when the upper range of the odor threshold
limit is less than the PEL, as determined by the critiqued and
approved data published by the American Industrial Hygiene Association,
"Odor Thresholds for Chemicals with Established Occupational Health
Standards" (1989, or as amended thereafter). That notwithstanding,
monitoring may be required to provide for the proper function
of the treatment system and other emergency controls. Moreover,
this exemption may apply only in those jurisdictions (i.e. Campbell,
Milpitas, Palo Alto, San Jose, Santa Clara, Sunnyvale) which provide
an exception based on the physiological warning properties of
certain gases. (09/19/91)
H. Treatment Systems
- Maximum release rates shall be calculated based upon a worst-case,
single event from a single cylinder, taking into account all engineering
- Restrictive flow orifices (RFOs) must be in the cylinder valve
to be considered in calculating the maximum release rate from
a cylinder. (06/21/90)
- Where cylinders are manifolded together, the maximum release
rate shall be the sum of the release rates for all of the manifolded
- All exterior storage shall be considered as one area when determining
the exempt amounts or the minimum threshold quantity of toxic
- It was the consensus of the TGO Committee that the issue of
"temporary storage" be handled by each individual jurisdiction.
- For the purpose of the TGO, an exhausted enclosure shall be
defined as an approved laboratory fume hood or process equipment
which is exhausted to a treatment system and protected by an automatic
- Exterior storage shall be defined as a storage area enclosed
by no more than two (2) contiguous walls, so as not to impede
exiting or confine air movement. (05/09/91)
J. Secondary Containment
- Secondary containment systems shall be approved and tested on
a case-by-case basis by individual jurisdictions. New types of
systems shall be evaluated by the TGO Committee as they are proposed.
- Secondary containment may not be required for systems operating
under sub-atmospheric conditions (i.e. vacuum piping systems)
if it is demonstrated that equivalent protection is provided (e.g.
When the system is equipped with an alarm and a fail-safe-to-close
valve activated by a loss in vacuum pressure). (11/29/90)
K. Portable Tanks and Cylinders
- For portable tanks and cylinders, the maximum flow rate of release
shall be based on the actual valve manufacturer 's specifications.
Where this data is not available, the maximum release rate may
be calculated by assuming the total release of gas from the cylinder
or tank within the time specified in Table No. 80.303-B of the
California Fire Code. (09/27/90)
- When portable tank or cylinder valves are equipped with approved
RFOs, the worst-case release shall be determined by the maximum
achievable flow rate, as determined by the valve manufacturer
or gas supplier's data.
- All portable toxic gas tanks and cylinders shall be marked to
indicate the valve's orifice size, in inches. The orifice size
shall be printed on the certification tag for the portable tank
or cylinder as well as on the vessel itself. The lettering shall
be 1/4" high, minimum, and be in contrast to the color it is printed
- Excess flow control valves, as defined in UFC, Article 80,
shall be permanently marked to indicate the maximum designed flow
rate, based on air under standard conditions.
- Encapsulating equipment designed to contain high pressure cylinders
and their contents, as approved by the Fire Chief, shall be acceptable
in meeting the intent of providing a gas cabinet or exhausted
enclosure for leaking gas cylinders. (03/27/91)
L. Inert Gas Purge Systems
- A dedicated inert gas purge system may be used to purge more
than one gas provided that the gases are compatible. (02/21/91)
- Purge gas systems shall be located in an approved gas cabinet
unless the system operates by vacuum demand.
M. Existing Ammonia Refrigeration Systems
- For facilities where ammonia refrigeration systems store more
than the Maximum Threshold Quantity (Max T.Q. = 12,500 lbs.) in
a single vessel, automatic valves shall be used to isolate zone
areas or equipment areas to less than the Max T.Q. Isolation shall
be achieved by shutting off the liquid supply to an area within
the system. The isolated area shall then be evacuated by suction
from the compressor. (03/02/93)
- The isolated area shall not contain more than 12,500 lbs.
of ammonia (calculated at normal temperature and pressure),
and shall provide pressure relief for both gas and liquid.
Pressure relief devices shall be directly connected to one
or more of the following:
i. Enclosed expansion chamber;
ii. Exhausted enclosure;
- Automatic isolation shall be provided for:
i. Seismic, fire, or other remote location alarm;
ii. Ammonia detection at 100 ppm, or at a concentration acceptable
to the individual jurisdiction,
not to exceed 250 ppm.;
iii. Emergency power failure;
iv. Exhaust system failure.
- Redundant ammonia gas detection shall be used to monitor non-welded
connections located within non-exhausted enclosures.
- Pipe valves shall meet current, nationally recognized standards
(i.e. California Codes and ASME/ANSI Standards) for threaded
and flanged valves.
- Sensors shall automatically isolate zone or equipment areas
upon detection at 100 ppm, or at a concentration acceptable
to the individual jurisdiction, not to exceed 250 ppm.
- Gas sensors shall be tested, at the discretion of the individual
- Approved vacuum procedures shall be used to purge an ammonia
- Information shall be submitted to the individual jurisdiction
which documents the vacuum purge procedure. Such information
shall, at a minimum, include:
i. Valve sequencing
ii. Ammonia flow directions
iii. Destination vessels
- A demonstration of the ammonia vacuum purge method (i.e.
the procedure used for a leak repair) shall be performed at
the discretion of the individual jurisdiction.
- Appropriate nationally recognized standards shall be used to
verify a "tight" system.
- Information shall be submitted to the individual jurisdiction
which documents that the system has passed pressure testing
in accordance with current, nationally recognized standards
(i.e. Uniform Codes and ASME/ANSI Standards) for pressure
testing of ammonia systems.
- An ammonia gas sensing device, approved by the individual
jurisdiction, shall be used to verify a "tight" system by
a qualified, independent testing firm or during inspection
conducted by the individual jurisdiction. Additional pressure
testing (at 150% of maximum anticipated operating pressure)
may be required at the discretion of the individual jurisdiction.
- Optional pressure testing (at 150% of maximum anticipated
operating pressure) may be required at the discretion of the