Ticking time bombs!

by Andre Mierzwa, Chief Engineer – FM Global

Over the last few years, fire protection servicing providers have seen an increase in the number of diesel fire pump starting battery “explosions”.  These explosions typically occurred as the diesel engine was manually started at the controller and causing battery acid to spray in many directions.  This is of serious concern.  Given the controller and batteries are typically in close proximity on fire pump installations, the person starting the engine could be doused in a spray of sulphuric acid causing serious injury.

This problem has come to the attention of WorkSafe Victoria, the Fire Protection Association Australia and the Standards Australia Committee FP 008 that is revising AS 2941 – Fixed Fire Protection Installations – Pumpset Systems.

So what is causing these explosions?

The typical starting battery for diesel driven fire pumps has been the flooded lead acid type that has removable caps to allow the electrolyte to be tested and topped up when necessary.  These are known as “stationary vented” type batteries.  The battery chargers for these are the continuous float (trickle) charge type that maintains the battery at or near full capacity.  Fire pump diesel engines also have alternators, however, due to their infrequent running and then only for short durations, the battery charger is the primary means of maintaining the battery fully charged.

With the advent of new sealed “maintenance free” batteries, also known as valve regulated lead acid batteries (VRLA), the norm for all vehicle starting, they have been used to replace the stationary vented type batteries on fire pumps without little to no consideration to the impact of the continuous float (trickle) charge on the battery.  In fact, the Australian Battery Industry Association (ABIA) have advised that the VRLA (automotive) type batteries are not designed for applications that involve continuous float (trickle) charge, as is near always the case in diesel engine powered fire pump applications.

With vehicles, the batteries are designed for starting, lighting and ignition (SLI) duties where the battery state of charge is maintained by the vehicle alternator while the vehicle is running – we do not see any battery chargers in our cars or trucks and if they are not run for a month or so, the likelihood of the battery being flat is high.  Fire pumps today are only started typically once a month and are usually run for about 10 minutes, so the alternators are not much use; hence the battery chargers within the pump controller are critical for maintaining the batteries ability to start the fire pump in an emergency.

We can now see that the VRLA (automotive) batteries are designed for use in vehicles where an alternator is used to charge them while the vehicle is running, whereas the stationary vented batteries are designed to be trickle charged while the engine is stopped for most of its life.

The Problem

What happens when you apply a trickle charge to a VRLA battery?

It all depends on the charger, the charging voltage, and battery temperature.  For VRLA batteries, overcharging is a significant problem because of its sealed design.  Overcharging dries out the electrolyte by driving the oxygen and hydrogen out of the battery through the pressure relief valves and the electrolyte cannot be replaced.  Over time the electrolyte level drops significantly to below the level of the plates.  On start-up of the diesel engine, the current draw required to drive the starter motor is high and this in turn drives off large volumes of oxygen and hydrogen which the relief valves cannot handle which over pressurizes the battery casing and cause it to rupture.  There is also the potential of internal damage and deposits within the battery resulting in a spark – combined with the hydrogen/oxygen mix being in the right range, it can result in a catastrophic battery explosion.

This process can take several months to reach a stage where a rupture or explosion could be imminent – hence the potential “ticking time bombs”!

Why is this happening?

With the introduction of AS 1851 – 2005 Routine Service of Fire Protection Systems and Equipment and now continued in the 2012 version, there is a requirement for the starting batteries on all diesel fire pumps to be replaced every 2 years, however the Standard does not provide any specific requirements other than conformance to AS 4029 (series) Stationary Batteries and compatability with the battery charger!  Because of the prevalence of the maintenance free, sealed VRLA batteries for automotive use and safer transport (no acid spill) considerations, these are provided as a replacement of choice for the “stationary vented” batteries that were originally installed.

The 2008 version of AS 2941 Fixed Fire Protection Installations – Pumpset Systems, requires an identification plate on the battery enclosure or cover with a warning stating “the use of non-complying batteries may lead to failure and potential rupture of the battery casing, due to internal pressure accumulation”.  A sample warning sign in the Standard states – “Warning, batteries must comply with AS 4029, non complying batteries may explode!

The issue has been recognised for a long time and warnings were within the Standard, however they have not been acted upon.  In my experience, I have not seen any warning signs on pumpset battery stands or covers. Further, unless the servicing personnel are fully conversant with AS 4029 and VRLA manufacturers technical manuals, they would not be aware of the consequences of installing VRLA batteries in place of vented stationary batteries!

Find the warning label on the fire pump battery stand in the picture gallery – note that it is a VRLA battery – a ticking time bomb!

What needs to be done?

WorkSafe Victoria in their Safety Alert dated November 2012 states:

•    Avoid using automotive type “maintenance free” batteries that have no provisions for periodic top-ups with water and/or monitoring of liquid levels in all cells where constant float charging is used.

•    Use (vented) stationary type batteries in backup (including fire pump) diesel engine applications.

•    If VRLA (batteries) are utilised in applications where average temperatures will be regularly above 25°C, charger voltage output control should have temperature compensation provision in accordance with battery manufacturer recommendations.  (Note low temperatures also impact charging and temperature compensation is advisable).

What do the manufacturers (EAST PENN) of VRLA batteries say?

•    It is critical that a charger be used that limits voltage.  A temperature-compensating, voltage-regulating charger, which automatically reduces the charge rate as the battery approaches the full charged state, shall be used.

•    Temperature is a major factor in battery performance, charging and voltage control.  At higher temperatures there is dramatically more chemical activity inside a battery.

•    A battery will “gas” near the end of charge because the charge rate is too high for the battery to accept.  A temperature-compensating, voltage regulating charger, which automatically reduces the charge rate as the battery approaches the fully charged state, eliminates most of this gassing.

•    Always use an automatic temperature-sensing, voltage-regulated charger! Set Boost/Absorption charge at 14.4 to 14.6 volts at 20°C.  Do not exceed 14.6 volts. Set Float charge at no higher than 13.8 volts.

•    Thermal runaway – A warmer battery requires a reduced voltage.  If the voltage is not reduced, current accepted by the battery increases and heating increases.  This can continue in a loop feeding on itself with the battery temperature and charging current rising to destructive levels!

•    Thermal runaway can be prevented with temperature compensation monitoring at the battery – not the charger – beware; many chargers measure the ambient temperature which could be significantly different from the battery’s internal temperature.

•    Undercharging allows the positive grids to corrode and the plates to shed, dramatically shortening battery life. The battery also has to work harder at a reduced capacity which makes it vulnerable to inadvertent over charging and eventual damage.

What will the next revision of the fire pump standard say?

There will be two options – it will still be acceptable to stay with the old “vented stationary” batteries and the trickle charge battery chargers, or provide VRLA batteries.  The requirements for both battery types will call for a battery charger that is capable of three stage charging consisting of boost, absorption and float stages.  For VRLA batteries, the charger will be required to sense battery voltage via separate cables independent from any voltage drop in the charging cables and where ambient temperatures are > 25 C or charge rate > 10A, temperature sensing at the battery shall be provided to regulate charge rate as well.  This is in accordance with the requirements from VRLA battery manufacturers.

Three phase charging

What do we do with existing installations where VRLA batteries have been provided yet the charger uses the old trickle charge method for charging?

Option 1:Check the battery by conducting a load test – if OK and the charger is voltage regulated and the maximum charge rate is at or below 13.8V and the ambient temperature is typically at or below 25 C, the situation may be tolerable – check with the battery manufacturer requirements.

Option 2:Replace the battery with a “Stationary vented” battery if the charger cannot be adjusted per option 1.

Option 3:If VRLA batteries are required – change the battery charger to comply with AS 2941 – 2013 – a three stage charger, with temperature compensation measured at the battery and separate battery voltage sensing cables.

In all cases, provide the appropriate warning and battery detail labels on or adjacent to the battery stand to be clearly visible.

Until the battery charger/battery combination is confirmed to be both compatible and safe, treat all fire pumpsets that have VRLA starting batteries as potential “ticking time bombs” and take all appropriate precautions.  ■

References:

Xantrex Technology, Inc SW Series Inverter/Charger

WorkSafe Victoria – Safety Alert – Preventing Battery Explosions November 2012

East Penn manufacturing Co., inc. Technical Manual Valve-Regulated Lead-Acid (VRLA):  Gelled Electrolyte (gel) and Absorbed Glass Matt (AGM) Batteries

Wikipedia – Automotive Battery

AS 2941 – 2008 Fixed Fire Protection Installations – Pumpset Systems

AS 2941 – 2013 – Draft

FM Approval Standard 1321/1323

FPA Australia Information Bulletin IB 01 – Fire Pump Battery Failures Version 1 Aug. 2011

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