• Gas and vapour risk zones
• Dust risk zones
• Explosion and combustion risk
• Intoxication risk
• Protection modes

Gas, vapours and dust are present in the work environment of many jobs across the spectrum of activities. Explosion or intoxication are a hazard for sewerage workers, firemen, wine producers and large industrial sites. By studying and making itself aware of the risks for each profession Oldham is able to develop the most suitable detection and alarm equipment for the needs.

Industrial risks may cause harm to persons, property, the environment and the company's activities. Increasingly strict regulations require operators to know these risks and take them into account. Working upstream of laboratories and regulatory bodies, Oldham proposes industrial and expert prevention and warning solutions suited to all environments and processes presenting a risk.

Gas and vapour risk zones

Directive 1999/92/EC defines three risk zones for gases and vapours.

Zone 0 « A location or atmosphere where an explosive mixture of air and flammable substances in the form of gas, vapour or mist is present frequently, continuously or for long periods.»
permanent explosive gaseous atmosphere

Zone 1 « A location or atmosphere where an explosive mixture of air and flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally»
probable or intermittent explosive gaseous atmosphere

Zone 2 «A location or atmosphere where an explosive mixture of air and flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for only a short period.»
accidental and brief explosive gaseous atmosphere

For each type of flammable gas and vapour, the following characteristics must be known :

• the LEL and UEL
• density in comparison with air
• flash point
• boiling point
• vapour pressure
• minimum ignition energy
• ignition temperature

Zones of potentially explosive dust

Directive 1999/92/EC also defines three risk zones for dusts:

Zone 20 «A location or atmosphere where a cloud of combustible dust in the air is present frequently, continuously or for long periods. »
permanent explosive dusty atmosphere

Zone 21 «A location or atmosphere where a cloud of combustible dust in the air is likely to occur in normal operation occasionally. »
probable or intermittent explosive dusty atmosphere

Zone 22 « A location or atmosphere where a cloud of combustible dust in the air is not likely to occur in normal operation but, if it does occur, will persist for only a short period»
accidental and brief explosive dusty atmosphere

For each type of combustible gas and vapour, the following characteristics must be known:

• grain size
• lower explosive limit
• ignition temperature of a cloud
• ignition temperature of a 5-mm layer
• minimum ignition energy (MIE)
• resistivity

Any explosion potential in predicable circumstances (relating to products, processes or the environment) creates an explosive atmosphere. Explosions or combustion result from a reaction between three elements:

• a combustible substance (gas or dusts)
• an oxidising substance (generally oxygen in the air)
• an energy source (spark, hot point)

This reaction is not systematic. Each type of gas or dust reacts explosively under given temperature and pressure conditions, determined by a lower explosive limit (LEL) and upper explosive limit (UEL). Risks are reduced by permanent monitoring of these limits.

Intoxication risk

Toxic gases derive from various sources:

• Combustion (CO-NO-NO2-SO2)
• Incineration (H2S-NH3-HCI)
• Fermentation (H2S-NH3)

Their passive or active presence is common in an industrial environment (chemical, petrochemical, cold chain, agri-foodstuffs), making it essential to detect them. They are also common in environments such as sewers, wine cellars or during fires, and must also be detected in these situations.

Intoxication risks are linked to the amount of time a subject is exposed to a harmful product. The danger is assessed in terms of time-weighted average (TWA) and short-term exposure limit (STEL). These values are expressed in weight (mg/m3) and volume (parts per million, ppm).

Protection modes