How Pyrogen Suppresses Fire

Introduction to Pyrogen Aerosol Fire Suppression Generators

Pyrogen is a self-generated Aerosol Fire Extinguishing Agent, and is one of the most efficient Halon Alternative products currently available.

The principle of extinguishing action employed by Pyrogen is unique - a special solid chemical, when electrically or thermally ignited, produces combustion products - micron sized dry chemical particles and gases. Dry chemical particles - mainly potassium carbonates, and gases - mainly carbon dioxide, nitrogen and water vapour, mix together into an uniform aerosol, which represents an actual extinguishing medium.

Before being released into a protected area, the hot aerosol propels itself through a solid chemical coolant, which decomposes, absorbing a great amount of heat, thus ensuring flameless discharge and uniform distribution of the aerosol within the area.

As aerosol is self-generated it requires no pressure cylinders and does not need to be stored. Pyrogenic mechanism of aerosol generation provides a sufficient driving force for a rapid discharge and efficient distribution of the aerosol. No piping is required.

The solid aerosol-generating chemical, together with the solid chemical coolant and ignition devices is contained in a small non-pressurised canister with one or two end-plate delivery nozzles. The canisters are called MAG generators and vary in size depending on the mass of solid aerosol-generating chemical contained in the generator.

MAG canisters are very compact and normally placed inside the protected enclosure. Operation of the generator is either electrical automatic, electrical manual or thermal automatic.

When an electric current is applied to the electric ignition device or alternatively naked flame or temperature above 175°C activates the thermal ignition device, it ignites the solid aerosol-generating chemical, which undergoes a chemical reaction of combustion to produce Pyrogen aerosol. The aerosol propels itself through the chemical coolant and out of the delivery nozzle into the protected area.

Pyrogen aerosol is whitish gas-like medium that is close in density to air. Small particle size ensures three-dimensional distribution qualities and long suspension times.

Pyrogen aerosol is non-conductive and non-corrosive.

As Pyrogen aerosol stays in suspension for extended periods, it can be removed from the protected area by any airflow. Solid fraction of the aerosol that has settled can easily be brushed, blown or washed away.

Pyrogen Chemical Description

The secret to Pyrogen’s’ power is in two unique formulations contained in Pyrogen canister - the solid aerosol-generating chemical and the solid chemical coolant.

The solid aerosol-generating chemical is a thermoplastic mixture consisting of an oxidiser, a combustible binder and technological additives. The oxidiser is a solid potassium nitrate (KNO_3(s)), the combustible binder is a solid plasticised nitro-cellulose (CnHmNpOq_(s)) and technological additives include carbon (C_(s)) as an activator of the oxidiser’s decomposition, chemical and mechanical stabilisers and some other ingredients.

When ignited the solid-generating chemical undergoes a combustion reaction, which can schematically be represented as follows:

KNO_{3 (s)} + CnHmNpOq _(s) + C_(s) = KHCO_3(s) + K₂CO_3(s) + CO_{2 (g)} + N_2(g) + H₂O _(g)

Combustion products consist of potassium carbonates (KHCO₃, K₂CO₃), carbon dioxide gas (CO_{2 (g)}), nitrogen gas ( N_{2 (g)} ) and water vapour (H₂O _(g)) and represent the actual extinguishing agent.

As the reaction temperatures are high, potassium carbonates are formed in the gas phase, but as the vapour cools, the potassium carbonates condense to a liquid and then a solid. As solid potassium carbonates are produced by condensation, the particle size is very small - approximately from 1 to 10 microns. Micron sized solid particles mix with the gaseous carbon dioxide, nitrogen and water into a uniform homogeneous gas-like phase - an aerosol.

Thus, Pyrogen extinguishing aerosol is a suspension of the micron sized solid particles, mainly potassium carbonates, in the gas mix of carbon dioxide, nitrogen and water vapour.

Being a combustion product of the aerosol-generating chemical, Pyrogen aerosol is hot upon formation. Although, Pyrogen aerosol is the most effective in terms of the actual fire extinguishment when in its hottest state, the negative impacts of very high temperatures are obvious. Ejection of flame at the discharge outlet and poor distribution within a protected enclosure is the main of those impacts and should be eliminated.

That is where a second unique formulation - the chemical coolant - comes into action.

When the hot Pyrogen aerosol passes through the coolant, the coolant decomposes absorbing a great amount of heat.

Pyrogen chemical coolant is a polymer composition highly impregnated with endothermic ingredients - substances that decompose at 200-300 °C without melting, generate gases and absorb approximately 400 Cal of heat per one kilogram of their mass. Cooling is effected at a fantastic rate of 400 degrees per second.

Application of the Pyrogen coolant enables the arrest flames at the discharge outlet and provides uniform distribution of the aerosol within the area, which certainly contributes to the reliability and safety of the extinguishment. Moreover, additional amounts of inert gases are formed due to a thermal decomposition of the coolant, which contribute to the effectiveness of the extinguishment.

Pyrogen Extinguishing Action

Pyrogen aerosol is an exceptional fire suppressant.

Pyrogen extinguishing action is achieved primarily by interfering chemically with the fire reaction. Two chemical mechanisms can be underlined:

1. Removal of flame propagation radicals - “chain carriers” OH, H and O in the flame zone:

As it has been mentioned above, the main component of Pyrogen aerosol - potassium carbonates - are formed in the gas phase. In the flame zone they dissociate producing potassium radicals K. Potassium radicals are very active and react with “chain carriers” OH, H and O removing them from the fire zone, and as such disrupting the fire reaction. The chemical action of potassium radicals in Pyrogen is similar to that of bromine radicals in Halons and can be schematically represented as follows:

K + OH = KOH

KOH + H = K + H₂O

2. Recombination of flame propagation radicals - “chain carriers” OH, H and O on aerosol particle surface:

Gaseous potassium carbonates condense to a liquid and then a solid form producing a large number of micron sized particles. Being so small, the particles produce a large surface area, where recombination of “chain carriers” takes place:

O + H = OH

H + OH = H₂O

Secondarily, Pyrogen extinguishing action is achieved by lowering fire temperature to a temperature below which the fire reaction cannot continue (thermal cooling). Several physical mechanisms can be underlined:

1. Heat absorption via endothermic phase changes:

K₂CO_{3 (s)} ® K₂CO_{3 (l)} ® K₂CO_{3 (g)}

2. Heat absorption via endothermic decomposition reaction:

2KHCO_{3 (s)} ® K₂CO_{3 (s)} + CO_{2 (g)} + H₂O _(g)

3. Dilution of the fire combustion zone by the aerosol cloud (additional fuel molecules cannot participate in the combustion process); physical hindrance to flame propagation (aerosol particles slow down velocity of a flame front propagation) etc.

The extremely high surface area of the micron-size aerosol particles increases the likelihood of radical recombination and heat absorbing reactions, thus ensuring rapid extinguishment with a small amount of agent.

Pyrogen has the lowest extinguishing concentration known among commercially available agents - flammable liquids (class B fires) are extinguished at the design factor of 100 g/m3 compared to 330 g/m3 for Halon 1301.

The high rate of aerosol discharge ensures a tremendous knockdown effect.

Micron sized aerosol particles exhibit gas-like three-dimensional qualities that allow the agent to rapidly distribute throughout enclosure and reach the most concealed and shielded locations. Homogeneous distribution is achieved in a matter of seconds, while long holding times all help to prevent fire re-ignition.

Canister Construction

Chemical Reaction of Pyrogen Fire Suppression Generators

The principle of extinguishing action employed by Pyrogen is unique - a special solid chemical, when electrically or thermally ignited, produces combustion products - micron size dry chemical particles and gases. Dry chemical particles, (mainly potassium carbonates), and gaseous mixture, (mainly carbon dioxide, nitrogen and water vapour), mix together into a uniform fire extinguishing aerosol. Before being released into a protected area, the hot aerosol propels itself through a unique solid chemical coolant, which decomposes absorbing huge amounts of heat, thus ensuring flameless discharge and uniform distribution of the cool aerosol within the area. The high rate of aerosol discharge ensures a tremendous knockdown effect. Micron size aerosol particles exhibit gas-like threedimensional qualities that allow the agent to rapidly distribute throughout enclosure and reach even the most concealed and shielded locations. Homogeneous distribution is achieved in a matter of seconds, while long holding times all help to prevent fire re-ignition.