does hydrostatic testing work?
understand how hydrostatic testing is used to check a
cylinder and/or hose assembly for leaks or flaws, let's
take a look at the procedure.
First, the extinguisher valve is removed and the threads
and interior of the cylinder are checked for corrosion,
pitting, and any other abnormalities [29 CFR 1910.157(f)(3)]. If the cylinder passes the visual inspection,
it is placed into a steel chamber, which is then filled
with water at normal pressure. A glass burette attached
to the side of the steel chamber will read zero, indicating
normal or zero pressure of the chamber water. Water is
then applied at high pressure to the interior of the extinguisher's
cylinder. As the pressure increases, the cylinder will
expand and push water from the steel chamber through a
small hole and into the glass burette. After the pressure
is released, the cylinder will contract and the water
will move from the burette back to the steel chamber.
Depending on the results, the tester will either pass
or fail the cylinder. The cylinder is normally considered
unsafe and will fail if:
- The water level in the burette continues to rise
while the specified pressure is applied. This could
be due to a leak from the inside cylinder to the water
in the steel chamber, or to a continual expansion
of the walls of the cylinder, both of which would
be a reasonable cause to fail the cylinder.
- The cylinder stretched and with the pressure released
does not return to its original size (or close to
it), it would mean the metal of the cylinder is not
resilient enough to be considered safe for use. The
burette can not have more then 10 percent of the displaced
water remaining after the pressure is released. For
example, if the expansion displaced 100 milliliters
(mL) of water, after it contracts it must have a reading
of 10 mL or less to pass the test.
of hydrostatic tests
The hydrostatic test described above is called the
water jacket type because the cylinder is enclosed
and surrounded by water during the testing process.
All compressed gas type cylinders (CO2, dry
chemical, etc.) must be hydrostatically tested using
this method. They must also have an expansion
indicator that operates with an accuracy within one
percent of the total expansion or .1cc (.1mL) of
liquid [29 CFR 1910.157(f)(15)(i)]
For all non-compressed gas type cylinders, you can
use a manual or powered hydrostatic test pump as
long as it meets the following requirements: [29 CFR 1910.157(f)(15)(ii)]
Do not use air or gas pressure for hydrostatic testing
because it compresses and expands many more times than
water, which makes it very dangerous [29 CFR 1910.157(f)(13)].
- It must be capable of producing at least 150
percent of the test pressure, and include the
appropriate check valves and fittings [29 CFR 1910.157(f)(15)(ii)(A)];
- It must have a flexible connection for attachment
to the test pump and necessary fittings to test through
the extinguisher nozzle, test bonnet, or hose outlet,
as applicable; and [29 CFR 1910.157(f)(15)(ii)(B)]
- Personnel must be physically protected during use
by a cage or barrier designed to allow visual
observation of the extinguisher during the test [29 CFR 1910.157(f)(15)(ii)(C)].
do portable extinguishers need to be hydrostatically tested?
ensure that your extinguisher will operate effectively
and safely, you are required to have them hydrostatically
is illegal and dangerous
to perform a hydrostatic test on any cylinder or shell
without first doing a visual external and internal
examination. If any component exhibits at least one of the
following conditions, it must be removed from service
immediately [29 CFR 1910.157(c)(5)];
Hydrostatically test portable extinguishers
at the intervals listed in
Table L-1, except under any of the following conditions:
- All soldered or riveted shell
self-generating soda acid or
- Self-generating foam or gas cartridge water
type portable extinguisher which you must invert
to rupture the cartridge to activate it or to
initiate an uncontrollable pressure generating
chemical reaction to expel the agent.
Hydrostatic Test Intervals
- When there have been repairs made by soldering,
welding, brazing, or with patching compounds [29 CFR 1910.157(f)(2)(i)];
- When the cylinder or shell threads are damaged [29 CFR 1910.157(f)(2)(ii)];
- When there are signs of corrosion that has
caused pitting, including corrosion under removable
nameplate band assemblies [29 CFR 1910.157(f)(2)(iii)];
- When the extinguisher has been burned in a fire
[29 CFR 1910.157(f)(2)(iv)].
Some signs of exposure to heat and fire are:
- Charring, blistering, or discoloration of
the cylinder paint or labels;
- Distortion of the cylinder body;
- Melting of any components (such as the valve
knob, the carrying handle, etc.); or,
- Activation of the valve pressure relief device.
- When a calcium chloride extinguishing agent has
been used in a stainless steel shell [29 CFR 1910.157(f)(2)(v)];
Depending on the type(s) of
extinguishers you have, they must be emptied and
hydrostatically tested at the intervals specified in Table
L-1. Extinguisher shells, cylinders, or cartridges that
fail a hydrostatic pressure test, or which are not fit for
testing, shall be removed from service and the workplace [29 CFR 1910.157(f)(14)].
Intervals (Table L-1)
(soldered brass shells)
be removed from service
acid (soldered brass shells)
*Soda acid (stainless steel shell)
Foam (stainless steel shell)
Test self-generating type
soda acid and foam extinguishers at 350 psi (2,410
kPa) [29 CFR 1910.157(f)(12)].
operated water and/or antifreeze
Stored pressure water and/or antifreeze
Aqueous Film Forming Foam (AFFF)
Dry chemical with stainless steel
(C02 extinguishers that
have a hose assembly equipped with a shut-off nozzle
must be tested at 1,250 psi (8,620 kPa) [29 CFR 1910.157(f)(6)].
Hose assemblies must also be tested within a
protective cage device [29 CFR 1910.157(f)(9)].
Dry chemical, stored pressure, with mild steel,
brazed brass or aluminum shells
Dry chemical, cartridge or cylinder operated, with
mild steel shells
Dry powder, cartridge or cylinder operated with
mild steel shells
Dry chemical and dry powder
hose assemblies equipped with a shutoff nozzle must
be hydrostatically tested at 300 psi (2,070 kPa) [29 CFR 1910.157(f)(7)].
Halon 1211 and all stored
pressure extinguishers must be hydrostatically
tested at the factory test pressure, not to exceed
two times the normal operating pressure [29 CFR 1910.157(f)(11)].
All hose assemblies must be hydrostatically
tested at the same interval as the extinguisher
if it is equipped with a shutoff nozzle at the
discharge end [29 CFR 1910.157(f)(5)].
Hose assemblies passing a hydrostatic test do
not require any type of recording or stamping [29 CFR 1910.157(f)(8)].
*Although still included in Table L- 1,
29 CFR 1910.157, Soda
acid (stainless steel shell) and Cartridge
operated water and/or antifreeze extinguishers are now obsolete.
records am I required to maintain?
For each extinguisher
in the workplace you must keep a record that includes:
This information should also
be securely fixed to each extinguisher, and provided
upon request to the Assistant Secretary as evidence
that the required hydrostatic testing of fire extinguishers
has been performed at the time intervals shown in
These records must be kept until the extinguisher
is hydrostatically re-tested at the time interval
specified in Table L-1 or until the extinguisher is taken
out of service, whichever comes first [29 CFR 1910.157(f)(16)].
- The name of the person or agency who performed
the last hydrostatic test, and the test date;
- The signature of the person who performed
- The serial number or other identifier of the
fire extinguisher that was tested.
- Test carbon dioxide extinguishers and nitrogen or
carbon dioxide cylinders used with wheeled
extinguishers every five years at 5/3 of the service
pressure as stamped into the cylinder. Nitrogen
cylinders that comply with 49 CFR 173.34(e)(15) may be
hydrostatically tested every 10 years [29 CFR 1910.157(f)(10)].
- Note: 49 CFR 173.34(e)(15) has been revised by
Hazardous Materials: Requirements for UN Cylinders (PDF).
OSHA Federal Register Final Rules 71:33894, (2006, June 12).
Further revision is also proposed by
Hazardous Materials; Miscellaneous Amendments.
OSHA Federal Register Proposed Rules 71:55757-55773, (2006, September 25).
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