The context: Risk of fire and gas explosions

For many businesses, limiting the risks of fire and gas explosions is a real problem. The use and storage of flammable products in a workplace significantly increases these risks.

What is fire?

A fire is an uncontrolled fire, neither in time nor in space. It is a chemical reaction of oxidation of a fuel by an oxidant. A fire is the result of the interaction of three elements, which together form the "fire triangle":

• fuel (wood, fabric, gasoline, etc.),
• the oxidant (oxygen, nitric acid, chlorine, etc.),
• a source of energy (electricity, flame, lightning, etc.).

To stop a fire or prevent a fire from starting, simply eliminate one of these elements.

There are different classes of fire, depending on the type of fuel.

• Class A involves a fuel such as wood, paper, plastic…
• Class B includes flammable liquids such as gasoline, diesel, white spirit, etc.
• Class B involves another category of flammable liquids: polar solvents (hydrogen, ethanol, propane, etc.)
• Class C involves electrical fires
• Class D involves fires involving flammable metals (aluminum, titanium, magnesium, etc.)
• Class F involves cooking oil fires

Knowledge of fire classes allows the implementation of appropriate prevention and control measures.

What is the explosion?

An explosion is an oxidation or decomposition reaction accompanied by a sudden increase in temperature and/or pressure. In the first case, it can occur within a mixture of flammable gas or dust with oxygen in the air or within an explosive product. In the second, the explosion generally occurs in a container and causes a burst.

Unlike a fire, an explosion causes a shielding effect accompanied by thermal and overpressure effects.

For an explosion to occur, several elements must be present. The causes of an explosion are the same as those of a fire: the presence of the "fire triangle". The difference is that three other elements are added:

• confinement,
• the presence of suspended products (gas, dust, fog, etc.)
• the explosive domain.

There are therefore six elements involved in an explosion. To eliminate the risk of fire and explosion, simply remove one of the components of the fire triangle. If one of the three remaining elements is removed, the risk of explosion is eliminated, but the risk of fire remains present.

The problem: Preventive measures

Regardless of the type of business, the employer must implement measures to prevent fire and explosion risks on its site. It must provide adequate safety equipment. Prevention of fire-related risks

Fire risk prevention consists of:

• detect and assess risks in order to limit their extent
• eliminate factors that can trigger a fire and spread the fire by implementing technical and organizational measures
• plan evacuations for staff and bystanders
• promote emergency response

To do this, several devices can be adopted. They can concern the construction aspect, by the choice of fire-resistant materials or by the multiplication of emergency exits for example. The devices can also be technical (alarm, smoke detector, signaling, fire extinguisher, etc.) or active (training, awareness, safety instructions, etc.).

The aim of fire risk prevention is to ensure the safety of workers and equipment and to respond effectively to the danger.

What are potentially flammable or explosive products?

Flammable products are products that can catch fire easily and quickly. They are liquids, solids, gases or vapors that can ignite or explode on contact with air and an energy source.

Among the flammable or explosive products that we encounter daily, we find gasoline, methylated spirits, white spirit or even paint. They are generally recognizable by the flammable pictogram (SGH02). Each flammable product is characterized by a flammability range between a lower and upper limit.

• The lower explosive limit (LEL) is the minimum concentration at which a combustible gas or vapour in air can catch fire. It is expressed as a % of volume in air. Below this threshold, the risk of fire or explosion is low.
• The upper explosive limit (UEL), also expressed in %, is the maximum threshold above which the product can ignite. Above this limit, ignition or explosion cannot occur because the concentration of the product is higher than the oxygen content.

In an ATEX zone, the control of the concentration of combustible gas or vapour outside the LIE and LES must be meticulous. The risks of fire and explosion are in fact greater there.

Our solution

Air Liquide is a world-renowned industrial group, a leader in its field, operating in the gas, technology and services sector for industry and health. Oxygen, Nitrogen and Hydrogen are the group's core business. It is therefore not surprising that this group must face challenges in terms of industrial safety linked to the nature of the products used.

We selected a high-performance temperature sensor for this customer to protect their gas cabinets.

Our approach

To meet the customer's expectations as closely as possible, we began with a listening and discussion phase between the Air Liquide design office and our engineers to define the customer's specifications and constraints. We then selected our Ex d Series TSDC temperature sensor range that best meets the application.

We have adapted the product to offer a tailor-made technological solution dedicated to the specific needs expressed: dual-blade detection/transmission technology, low temperature trigger threshold, armored cable, 316L stainless steel design and special mounting kit.

This need does not correspond to the standards usually found on the market and given the vital importance of these sensors for the safety of installations. It is easy to imagine what the impact of a faulty sensor could be!

We therefore developed prototypes so that the Air Liquide design office could carry out tests in order to technically validate the product and then reference it.

Product Highlights

The ATEX sensor TSDC-BTS Series is a temperature detection and control sensor. It is composed of an explosion-proof enclosure and cables that are highly resistant to high temperatures. The ATEX sensor TSDC-BTS Series is configured from a switch housed in the explosion-proof housing. This consists of two thermosensitive metal elements.

This thermal sensor protects a machine from overheating by cutting off its circuit when the nominal switching temperature is reached. Once the machine cools down to its reset temperature, the switch returns to its initial state and the circuit is completed.

The ATEX sensor TSDC-BTS Series is available in two sizes: 35 mm and 65 mm (inner dimension). For better pressure resistance and sealing, its tube and body have been assembled. This type of sensor is suitable for different fields such as pharmaceutical, petrochemical or refinery. It can be used in zones 1/21 and 2/22.

A2s' attentiveness and responsiveness were once again demonstrated in this request from Air Liquide, which required a strong contribution from our design office in order to deliver a safe and sustainable solution. Responding to challenges of this type is part of our DNA. We can thus express our full involvement alongside our customers to find solutions.