EU F-Gas regulations – Flammability Issues

Flammability Issues

EU F-Gas regulations – Flammability Issues


This guidance is for organisations affected by the 2014 EU F-Gas Regulation (517/2014). The F-Gas
Regulation creates controls on the use and emissions of fluorinated greenhouse gases (F-Gases)
including HFCs, PFCs and SF6. The 2014 EU F-Gas Regulation replaces the 2006 Regulation,
strengthening all of the 2006 requirements and introducing a number of important new measures.

A key feature of the 2014 F-Gas Regulation is the introduction of the phase down in the supply of HFCs
within the EU market. This will lead to an 80% cut in the amount of HFCs that can be sold in the EU
by 20301

. To achieve such significant cuts, the users of HFCs will need to start using alternative fluids
with much lower global warming potentials (GWPs) than the current HFCs2

. Many of the low GWP alternatives to HFCs are flammable – this creates potential safety issues and may restrict their usage.

This Information Sheet provides guidance on the impact of using flammable HFC alternatives.

Non-flammable HFCs

EU F-Gas regulations – Flammability Issues


Most HFCs are non-flammable and this is a characteristic that made HFCs a popular choice for many
end user applications. Key uses of non-flammable HFCs include:

• Refrigeration, air-conditioning and heat pumps (RACHP)
• Technical and medical aerosols
• Insulation foam
• Fire extinguishing fluids

The non-flammable property of most HFCs makes it relatively easy to manufacture, install and
maintain equipment such as RACHP systems. If some non-flammable refrigerant leaks there will be
no risk of fire. Similarly, an aerosol using a non-flammable HFC propellant may be safer to use in
circumstances where there may be a source of ignition.

One of the reasons that most HFCs are non-flammable is that their molecular structure is very stable.
Unfortunately, this property also gives HFCs a very long atmospheric life and a high GWP. Low GWP
alternatives usually have less stable molecules – this is good from a GWP perspective, but it results in
many alternatives being flammable.

Flammability is not a simple issue

EU F-Gas regulations – Flammability Issues


If there are plenty of non-flammable options available it is easy to apply a simplistic approach to
flammability: if a flammable fluid is undesirable, safety codes take a conservative view and state that
flammable fluids cannot be used.

This simplistic approach is not ideal when there are fewer non-flammable fluids to choose from. To
make more widespread use of low GWP alternatives, it is important to recognise that there are widely
varying “levels of flammability”. There is a continuous spectrum of flammability which includes:

• Highly flammable fluids – these are very easy to ignite and can burn with explosive impacts.

The most common examples are hydrocarbons (HCs) such as propane and butane. These have
very useful properties for use as refrigerants, aerosol propellants and foam blowing agents.
However, they are also used as fuels and they can be ignited very easily.

• Flammable fluids – they are more difficult to ignite, but once ignited will continue to burn and
could create a significant hazard.

• Mildly flammable fluids – these are very difficult to ignite, they burn “gently” and might be
extinguished when the source of ignition is removed. Mildly flammable fluids create a smaller
fire risk than an equivalent amount of a more flammable fluid.

• Non-flammable fluids – these cannot be ignited

Existing safety codes do not properly distinguish between different levels of flammability. For example
EN 378 2008 (“Refrigerating systems, safety and environmental requirements”) only has 3 categories
of flammability which are based on a simplified set of flammability parameters. EN 378 is currently
being updated to include a 4th flammability category, although that may still prove to be an oversimplification that restricts the use of mildly flammable fluids.

A problem faced by both the authors of safety codes and users of flammable fluids is that flammability
is a complex issue and it is not easy to find a simple way of defining a safe operating envelope for each
fluid. Flammability can be measured in a number of ways.

The most important parameters include:

1) LFL, lower flammability limit. LFL is the minimum concentration of a gas or vapour that is
capable of propagating a flame within a homogeneous mixture of that gas or vapour and air.

2) UFL, upper flammability limit. UFL is the maximum concentration of a gas or vapour that is
capable of propagating a flame within a homogeneous mixture of that gas or vapour and air.

3) HoC, heat of combustion. HoC is the energy released as heat when a compound undergoes
complete combustion with oxygen under standard conditions.

4) BV, burning velocity. The BV is the speed at which a flame propagates.

5) MIE, minimum ignition energy. The MIE indicates how much energy must be in an ignition
source (e.g. a spark or naked flame) to initiate ignition of a gas or vapour.

The safety code EN 378 2008 uses LFL and HoC to distinguish between highly flammable, flammable
and non-flammable fluids. In the revised code currently being written, it is expected that a new
category of “mildly flammable” is to be introduced, based on those fluids that have a low burning
velocity.

Table 1:

Class 3: Highly flammable: 19
Class 2: Flammable: >0.1 and 0.1 and <19
Class 1: Non-flammable: Cannot be ignited

The flammability issue is made even more complicated by various other effects that influence
combustion. Three important examples are:

a) The exact geometry of an ignition source can change the MIE – a spark between thin
electrodes will ignite a gas with less energy than a spark between thick electrodes (due to the
effect of heat removed from the combustion zone, via conduction along the electrodes).

b) High air humidity can increase the burning velocity of some fluids; for example the BV of HFO
1234yf is 1.5 cm/s in dry air, but 5.9 cm/s in very humid air. However, this effect does not
occur for all fluids. For example, HFC 32 has a BV of 6 cm/s at all levels of humidity.

c) A dilution effect occurs when a leaking gas mixes with the air around it. For a highly flammable
gas, the LFL is low and a lot of dilution must occur before the gas concentration drops to below
the LFL. For mildly flammable gases, the LFL is much higher and dilution below the LFL can
occur much more quickly. Figure 1 illustrates this effect (which can also be affected by gas
density). The highly flammable propane leak rate is only a quarter of the leak rate for mildly
flammable HFC 32, but it creates a much greater “ignition risk footprint” (the red area).

These issues have been discussed to illustrate the high complexity of the flammability issue. Safety
codes must take a conservative approach in the absence of sufficient technical data.

Likelihood and Severity of Risks

EU F-Gas regulations – Flammability Issues


 

 

It is important to distinguish between the likelihood of ignition and the severity of the consequences
of ignition.

The likelihood of ignition depends significantly on the LFL and the MIE:

• A highly flammable fluid has a low LFL (i.e. there only needs to be a small amount of the gas
mixed with air for ignition to be possible) and a low MIE (i.e. a low energy ignition source such
as a small spark will cause ignition).

• A mildly flammable fluid has a higher LFL – this means there will be a smaller area in which
there is risk of ignition (in most normal circumstances, as illustrated in Figure 1). It also
requires a much higher MIE, which means there needs to be a much more powerful ignition
source located in the risk of ignition area.

The severity of the consequences of ignition depends significantly on BV and HoC:

• A highly flammable fluid has a high BV – this can lead to explosive ignition within a cloud of
gas that is above the LFL. If the HoC is also high, then the damage caused by the burning gas
will be greater.

• A mildly flammable fluid has a low BV – in the situation where ignition occurs, the burning
takes place slowly. Burning cannot be sustained if the air velocity is higher than the BV and it
might not be sustained if the ignition source is removed.

Flammability Class 3 gases (highly flammable) such as propane exhibit both a high likelihood of ignition and a high severity of consequences following ignition.

Flammability Class 2L gases (mildly flammable) such as HFO 1234yf or HFC 32 are relatively difficult to
ignite (both in terms of high LFL and high MIE) and their low BV makes the consequences of ignition
much less severe.

Table 2:

Fluid           Flammability class             LFL          MIE 5         HoC                 BV
                                                                 kg/m3          mJ        MJ/kg          cm/s

Propane                      3                            0.028         0.3             46                  43

HFC 152a                    2                            0.130           10            16                  23

Ammonia                    2L                          0.116         100            19                    7

HFC 32                        2L                          0.307       1000             9                     6

HFO 1234yf                2L                           0.289       5000             9                  1.5

The data in Table 2 clearly show that a class 3 fluid is very easy to ignite (very low LFL and MIE) and
that the consequences of burning can be severe (high BV and high HoC).

It is interesting to note that ammonia has been widely used in large industrial systems for many years.
There are very few cases of fire related to an ammonia leak (due to the difficulty of ignition).
HFC 152a has a higher LFL and lower HoC than ammonia. Based on previous safety codes that would
indicate that HFC 152a is “less flammable” than ammonia. However, practical experience indicates
that HFC 152a is much more readily flammable than ammonia. This can be explained by the low MIE
(making ignition much easier) and the high BV (making the consequences more severe). This shows
the importance of avoiding a simplistic way of categorising flammability.

Ultra-low GWP fluids such as HFO 1234yf and moderate GWP fluids like HFC 32 are important
alternatives that could help meet the EU HFC phase down targets. The data in Table 2 indicates that
these fluids are much more difficult to ignite (much higher MIE and LFL than ammonia) and that
consequences of ignition are more limited (low BV and Low HoC).

These are encouraging characteristics, although it must be stressed that until safety codes have been revised it is difficult to define the safe “operating envelope” for fluids of this type.

What does this mean for equipment manufacturers and end users?

EU F-Gas regulations – Flammability Issues


 

 

To achieve a rapid phase down in the use of high GWP HFCs, it is likely that there will need to be a
greater use of flammable fluids.

The safe operating envelop for well-established flammable fluids such as propane and ammonia can
be established using existing safety codes such as EN 378 2008. In the case of propane and other
hydrocarbons (HCs) this severely limits the applicability of these fluids except in very small systems
(e.g. sealed refrigeration systems with less than 0.15 kg of refrigerant). For ammonia, the key safety
issue is toxicity and this restricts the use of ammonia outside restricted locations such as factories and special plant rooms.

The safe operating envelop for new fluids such as HFO 1234yf and HFC 32 will need to be established
over a period of time, based on increasing levels of practical experience and further technical research.

This is likely to proceed in 3 stages:

a) Existing codes can be used immediately. Whilst these do not give full credit for the mildly
flammable characteristics, they still allow much greater refrigerant charge than for HCs. For
example a charge limit might be 1 kg for HCs and 7.8 kg for HFC 326 This allows quite widespread application in small retail refrigeration and small air-conditioning systems.

b) Revised codes are likely to be available by the end of 2015. These will widen the operating
envelope for mildly flammable fluids (e.g. the charge limit quoted above would rise from 7.8
kg to 11.7 kg for HFC 32). This will enable a greater range of application than the current
codes.

c) Within another few years it is likely that codes will be revised again, to take account of
practical experience and new research. These may allow even larger charges to be used,
although that clearly depends on the nature of the experience gained.

The SRAC industry and the world as a whole, now understand that fluorinated gases have a potentially devastating global warming effect when released into the atmosphere.

F-Gas regulations have been implemented in order to contain, prevent and thereby reduce emissions of fluorinated greenhouse gases.

On 2nd April 2008, the Commission Regulation 303/2008 set out the requirements for a company certification scheme.

This scheme is specifically for businesses working with F-Gas refrigeration, air-conditioning and heat pump equipment containing or designed to contain fluorinated greenhouse gases.

These F-Gas Certification requirements are in accordance with Article 5.1 of EC Regulations 842/2006 on certain fluorinated greenhouse gases (the EC F-Gas Regulation).