Working safely around suppression systems

Most injuries and accidental discharges involving suppression systems do not happen during fires. They happen during inspection, testing, maintenance, construction and ordinary work in protected spaces, when someone disturbs a detector, a release circuit, an actuator or a cylinder without the right precautions. This lesson brings together the practical rules for working safely on and around gaseous suppression systems: putting systems into manual or lockout, handling high-pressure cylinders, inspecting agent quantity and pressure, controlling hot work and dusty work in protected areas, and restoring systems afterwards. Water-based impairments were covered in Lesson 7; this lesson applies the same ideas to clean agent and carbon dioxide systems.

HSE-210, Lockout and Hazardous Energy Control, covers the principles of controlling hazardous energy, which apply here because a charged cylinder is stored energy and a release circuit is a control system that can start it. HSE-250, Transportation of Dangerous Goods Awareness, covers moving cylinders on public roads. HSE-216, Hot Work Safety, covers hot work in general.

Who may work on suppression systems

Inspection, testing, maintenance and repair of suppression systems are specialist work. The fire protection contractor's technicians, trained on the specific system and manufacturer, handle actuators, cylinders, valves, releasing panels and agent. Site staff may be trained to carry out a limited set of tasks under a written procedure, such as checking gauges, recording panel status, placing a system in manual using a keyed switch, and acting as a fire watch. Everyone else, including electricians, cablers, mechanical contractors and customers, must know enough to avoid disturbing the system and to recognize when work needs an impairment permit.

Automatic, manual and lockout

A clean agent or carbon dioxide system can usually be placed in one of several states, and the names vary between manufacturers and sites. The states that matter to people are these.

The key distinction is between electrical isolation and mechanical lockout. Disabling release circuits at the panel prevents the panel from firing the actuators, but it does not prevent a discharge caused by a mechanical manual release at the cylinders, by an actuator fired by stray voltage while wiring is being disturbed, or by a technician working on the wrong circuit. For work on the system itself, and for any work inside a carbon dioxide protected space, a mechanical means of preventing discharge into the space is needed: a supervised lockout valve in the discharge piping, as NFPA 12 requires for carbon dioxide systems, or physical removal of the actuators from the cylinder valves as specified by the manufacturer. NFPA 2001 likewise requires means to prevent discharge of clean agent systems during maintenance.

Every change of state is an impairment. It must be authorized, recorded, communicated to the monitoring station and the people in the area, and reversed afterwards with a check that the system is back in its normal state. One of the most common findings after fires in protected rooms is that the system was left in manual or disabled after earlier work and did not discharge.

The release circuit is a live control system

Electric actuators on clean agent cylinders are fired by a pulse of current from the releasing panel. They are designed to be reliable, which means they fire readily when current flows. A technician who disconnects or reconnects actuator wiring while the panel is armed, tests continuity with the wrong instrument, or shorts a release circuit can fire the actuator and discharge the system. Manufacturers therefore specify a strict order for work: disable the release at the panel, then remove the actuators from the cylinder valves and place them in a safe position or fit them with test devices, before any work on the release circuits or the cylinders; and on restoration, reconnect and test the circuits with the actuators off the cylinders, confirm the panel is normal, and refit the actuators last.

High-pressure cylinders

A suppression cylinder stores energy in compressed gas. An inert gas cylinder at 200 to 300 bar (about 2,900 to 4,400 psi) holds enough energy to turn the cylinder into a projectile if its valve is knocked off, and halocarbon cylinders, though at lower pressure, are heavy and still dangerous. Discharge through an unrestricted valve outlet produces a strong reaction force. Safe handling follows the general rules for compressed gas cylinders, with some additions for suppression systems.

• Keep cylinders secured in their brackets at all times when installed, and secure spare or removed cylinders upright and chained or strapped.
• Fit the valve protection cap and the outlet safety device, often called an anti-recoil or safety cap, whenever a cylinder is disconnected from its discharge hose. The device diverts the gas so that an accidental discharge does not produce a strong thrust.
• Never move a cylinder with its discharge hose or actuator attached, and never move one without its protection cap. Use a suitable cylinder cart; do not roll heavy cylinders by hand or drag them.
• Keep cylinders within their rated temperature range and away from heat sources, because pressure rises with temperature.
• Do not attempt to open, repair or refill a cylinder on site unless you are a qualified technician following the manufacturer's procedure.
• Treat a cylinder that has been dropped, damaged, exposed to fire or found with a damaged valve as hazardous; keep people away and call the fire protection contractor.

Inspecting agent quantity and pressure

NFPA 2001 and NFPA 12 require periodic checks that the cylinders still contain enough agent and pressure, commonly at six-month intervals, in addition to monthly visual inspections. Halocarbon cylinders are checked by weighing them or by using a liquid level indicator, and their pressure is checked against the manufacturer's chart for the cylinder temperature. Inert gas cylinders are checked by pressure, adjusted for temperature. A common rule in NFPA 2001 is that a halocarbon container must be refilled or replaced if it has lost more than 5 percent of its agent or more than 10 percent of its pressure after temperature correction, and an inert gas container if it has lost more than 5 percent of its pressure after correction. Carbon dioxide cylinders are weighed, and a loss of more than 10 percent of agent weight requires action. These are summaries; the edition in force and the manufacturer's instructions govern.

Temperature correction matters because cylinders in a cold or warm room show pressures that differ from the reference value even when no agent has been lost. The program below corrects inert gas cylinder pressures to a reference temperature using the ideal gas law and flags cylinders below the illustrative 5 percent criterion. The readings are invented.

# Teaching check of inert gas cylinder pressures, corrected to 15 degC.
REF_C, NOMINAL_BAR, LIMIT = 15.0, 300.0, 0.05   # illustrative values
def corrected(p_bar, t_c):
    # ideal gas: P/T constant for fixed gas quantity (absolute temperatures)
    return p_bar * (REF_C + 273.15) / (t_c + 273.15)

readings = [  # cylinder, gauge bar, room degC
    ("IG-01", 304.0, 18.0), ("IG-02", 296.0, 18.0), ("IG-03", 282.0, 18.0),
    ("IG-04", 286.0, 8.0), ("IG-05", 311.0, 24.0),
]
for cyl, p, t in readings:
    pc = corrected(p, t)
    loss = (NOMINAL_BAR - pc) / NOMINAL_BAR
    status = "REFILL OR REPLACE" if loss > LIMIT else "ok"
    print(f"{cyl}: gauge {p:5.1f} bar at {t:4.1f} C -> {pc:5.1f} bar at 15 C, "
          f"loss {100*loss:4.1f}%  {status}")

IG-01: gauge 304.0 bar at 18.0 C -> 300.9 bar at 15 C, loss -0.3%  ok
IG-02: gauge 296.0 bar at 18.0 C -> 293.0 bar at 15 C, loss  2.3%  ok
IG-03: gauge 282.0 bar at 18.0 C -> 279.1 bar at 15 C, loss  7.0%  REFILL OR REPLACE
IG-04: gauge 286.0 bar at  8.0 C -> 293.1 bar at 15 C, loss  2.3%  ok
IG-05: gauge 311.0 bar at 24.0 C -> 301.6 bar at 15 C, loss -0.5%  ok

Cylinder IG-03 has lost more than 5 percent after correction and must be refilled or replaced. Cylinder IG-04 reads low on the gauge, but only because its room is cold; after correction it is within limits. Cylinder IG-05 reads high for the same reason in reverse. Real inspections use the manufacturer's correction chart, especially for halocarbon agents, whose pressure depends on both the nitrogen and the vapour pressure of the liquid and does not follow the simple gas law.

Cylinders must also be requalified periodically under transport rules, which means they are emptied and tested, typically by a hydrostatic test, at intervals set by Transport Canada or the US Department of Transportation and the cylinder specification. A cylinder removed for retest leaves the system without part of its agent, so cylinder replacement programs are planned as impairments with spare cylinders or alternative protection.

Hot work and dusty work in protected areas

Hot work, such as welding, cutting, grinding and soldering with a torch, in or near a protected room creates two problems. The heat, smoke and dust can trigger the detection system and cause an unwanted discharge. And if a halocarbon agent is present, perhaps from a leak or a recent discharge, hot surfaces and flames can decompose it to hydrogen fluoride. Hot work in protected areas therefore needs a hot work permit, a planned impairment that places the release in manual or lockout and isolates only the detectors that the work would affect, a fire watch during the work and for a period afterwards, and confirmation that no agent is present. Dusty work, such as core drilling, cutting gypsum board and sanding, needs the same impairment and dust control, as Lesson 3 described.

Working in carbon dioxide protected spaces

Where carbon dioxide total flooding systems remain, entry into the protected space is controlled more strictly than for clean agents. Before anyone enters, the system must be locked out mechanically using the supervised lockout valve or another means specified by the manufacturer, the lockout must be verified, and the person entering must hold the key or lock. The space should be checked for residual carbon dioxide and oxygen deficiency, particularly in low areas, before entry, and signs must be in place. Adjacent low spaces into which gas could flow, such as pits and basements, should be checked too. These requirements apply to every entry, however brief, and they are commonly built into the site's lockout and confined space procedures.

Restoring systems

Restoration is where many incidents begin. A system left in manual, an actuator left off its cylinder, a lockout valve left closed or a detector left covered will leave a room unprotected, often without anyone noticing until a fire. A good restoration procedure includes a physical check of every item changed during the work, a check of the panel for normal status with no supervisory or trouble signals, notification of the monitoring station and the people told of the impairment, and a second person's verification for critical systems. Shift handovers should review all open impairments.