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.
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
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.
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:
- It must be capable of producing at least 150 percent
of the test pressure, and include the appropriate
check valves and fittings;
- 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
- Personnel must be physically protected during use
by a cage or barrier designed to allow visual observation
of the extinguisher during the test.
not use air or gas pressure for hydrostatic testing because
it compresses and expands many more times than water,
which makes it very dangerous.
do portable extinguishers need to be hydrostatically tested?
ensure that your extinguisher will operate effectively
and safely, you are required to have them hydrostatically
or 12 years, depending on the type of extinguisher.1910.157(f)(2)
||Whenever they show
new evidence of corrosion or mechanical injury.
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;
Hydrostatically test portable extinguishers
at the intervals listed in
Table L-1, except under any of the following conditions:
- The shell is of copper or brass construction
joined by soft solder or rivets; or,
- You must invert the extinguisher to activate
Hydrostatic Test Intervals
- When there have been repairs made by soldering,
welding, brazing, or with patching compounds;
- When the cylinder or shell threads are damaged;
- When there are signs of corrosion that has caused
pitting, including corrosion under removable nameplate
- When the extinguisher shows signs of exposure
to high heat or fire;
- 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;
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 must be removed from service. 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
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).
1910.157(f)(6) Hose assemblies must also be
tested within a protective cage device.
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).
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.
hose assemblies must be hydrostatically tested
at the same interval as the extinguisher if it
is equipped with a shutoff nozzle at the discharge
1910.157(f)(5) Hose assemblies passing a hydrostatic
test do not require any type of recording or stamping.
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
Table L-1 or until the extinguisher is taken
out of service, whichever comes first.
- 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.