EN 250 Respiratory Equipment - Open Circuit Self-Contained Compressed Air Diving Apparatus - Requirements, Testing and Marking

The European standard “EN 250 Respiratory equipment - Open-circuit self-contained compressed air diving apparatus - Requirements, testing and marking” describes the minimum requirements for self-contained open-circuit compressed air underwater breathing apparatus and sub-assemblies to ensure safe operation at depths of up to 50 metres.

This standard applies to self-contained open circuit compressed air underwater breathing apparatus. The purpose of the requirements and tests specified in this standard is to ensure a minimum level of safe operation for the underwater breathing apparatus up to a maximum depth of 50 metres.

This standard includes laboratory and practical performance tests to assess conformity with the requirements.

For the purposes of this standard, the following terms and definitions apply (these are generally taken from the EN 132 standard):

Self-contained, open-circuit compressed air underwater breathing apparatus means an apparatus having a portable source of compressed air carried by the diver, which enables the diver to breathe underwater (abbreviated as SCUBA). The SCUBA consists of a number of self-contained elements which, when ready for use, comply with the requirements of this standard and are functionally compatible with each other. When connected together, the complete SCUBA is designed to enable the user to breathe air on demand from a high-pressure cylinder via a demand regulator connected to a face piece. Exhaled air passes from the demand regulator into the ambient water via the exhalation valve without being recirculated.
High pressure refers to the pressure inside the air cylinders and between the air cylinders and the pressure reducer.
Intermediate pressure refers to the pressure between the pressure reducer and the demand valve.
Low pressure refers to the pressure inside the facepiece, approximately ambient pressure.
Nominal working pressure refers to the maximum working pressure of the relevant components.
Reference pressure refers to the equilibrium pressure at the facepiece when there is no breathing gas flow.
Respiratory pressure refers to the differential pressure across the facepiece (relative to the reference pressure measured during inhalation and exhalation)
Respiratory pressure refers to the differential pressure across the facepiece (relative to the reference pressure measured during inhalation and exhalation)
Opening negative pressure (crack pressure) refers to the respiratory pressure during inhalation required to open the inhalation valve.
Displaced (tidal) volume refers to the volume of respiratory gas displaced by the respiratory simulator during one half cycle (inhalation or exhalation) (measured in litres).
Respiratory frequency refers to the setting of the respiratory simulator, measured in cycles per minute.
Respiratory frequency refers to the setting of the respiratory simulator measured in cycles per minute.
Respiratory minute volume or ventilation rate returns the product of tidal volume and respiratory frequency measured in litres per minute.
Pressure volume loop refers to the diagram created during a respiratory cycle by plotting respiratory pressure against displaced volume.
The work of breathing is the work done during a respiratory cycle. This work is generally proportional to the area bounded by the pressure-volume loop. The work associated with positive pressures during inhalation is not included in the total work of breathing.
A face mask refers to a device used to connect a device to the user. It can be a mouthpiece assembly or a full face mask or diving helmet.
A mouthpiece device refers to a device that is usually held by the teeth, forms a seal against the lips, and through which air is inhaled and exhaled.
A full face mask is a face piece that covers the mouth, nose, eyes, and chin and may be fitted with a mouthpiece or inner mask.
A diving helmet is a face piece that covers the entire head and can be equipped with a mouthpiece or inner mask.
Dead space is the volume of space formed between the mouth and the inhalation and exhalation parts.

The SCUBA must be equipped with at least the equipment described above (air cylinders, demand regulator, safety device, carrying frame or holding device for air cylinders, facility for attaching the safety belt, carrying system, face piece (such as mouthpiece assembly or full face mask or diving helmet) and instructions for use.

The SCUBA and its subassemblies must be designed and its components positioned in such a way as to provide protection against mechanical damage from external factors and to enable the necessary functional checks to be carried out before diving. The combination of components must not adversely affect the safe operation and use of the device. In the case of multiple cylinders connected to each other, care must be taken to ensure that pressure equalization between open cylinder valves or open reserve valves is not obstructed.

SCUBA and subassemblies must not have protruding parts or corners and edges that could injure the diver. All parts that must be operated by the diver during use must be accessible and controllable, even when wearing protective gloves. They must be designed so that their settings cannot be inadvertently changed during use.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “EN 250 Respiratory equipment - Open circuit self-contained compressed air diving apparatus - Requirements, testing and marking” standard with its trained and expert staff and advanced technological equipment.