The new EN 1127-1:2011 standard; influences and application
08 February 2013
Applying a new standard to a process is, in many cases, an exercise of ‘once and done’, but not with EN1127-1:2011. In this article, we take a look at the key changes in the Standard and the contributing factors that influence its application including protective systems and the application of functional safety.
With the release of EN 1127-1 2011 Edition, “Explosive atmospheres – Explosion prevention and protection – Part 1: Basic concepts and methodology,” hazards from explosions are now to be considered in accordance with this standard alongside EN ISO 12100, which specifies basic terminology, principles and a methodology for achieving safety in the design of machinery. It specifies principles of risk assessment and risk reduction that are based on knowledge and experience of the design, use, incidents, accidents and risks associated with machinery.
Procedures are described for identifying hazards and estimating and evaluating risks during relevant phases of the machine life cycle, and for the elimination of hazards or sufficient risk reduction. Guidance is given on the documentation and verification of the risk assessment and risk reduction process. As indicated in Section 1 of the Standard, understanding the application of EN 1127-1 will help designers and manufacturers in achieving explosion safety in the design of equipment, protective systems and components at all stages of its use. It is applicable to any equipment, protective systems and components intended to be used in potentially explosive atmospheres, under atmospheric conditions.
Changes between EN1127-1:2007 and EN1127-1:2011
i) The risk assessment now includes reference to EN15198 ‘Methodology for the risk assessment of non-electrical equipment and components for intended use in potentially explosive atmospheres’ in addition to EN ISO 12100. Essentially the risk assessment aspect has been modified to include the frequency of occurrence of the potential ignition source and the flammable atmosphere and sources are classified:
* Sources of ignition which can occur continuously or frequently;
* Sources of ignition which can occur in rare situations;
* Sources of ignition which can occur in very rare situations.
ii) The inclusion of ‘Tightness of Equipment’. The formation of a hazardous explosive atmosphere outside the equipment can be prevented or limited by means of the tightness of the equipment. Here, a differentiation is made between:
* Equipment which is durably technically tight
* Technically tight equipment where the escape of flammable materials is due to operation.
Equipment which is durably technically tight:
a) In the case of equipment which is durably technically tight, no release is to be expected.
b) Equipment is regarded as durably technically tight, if: it is constructed such that it remains technically tight due to its design; or its technical tightness is permanently ensured by means of maintenance and supervision.
c) Equipment with a durably technically tight construction does not cause any hazardous areas in its surroundings while closed.
iii) EN 1127-1 (page 5) also specifically addresses explosion hazards that can occur from:
* materials processed or used by the equipment, protective systems and components;
* materials released by the equipment, protective systems and components;
* materials in the vicinity of the equipment, protective systems and components;
* materials of construction of the equipment, protective systems and components.
By conducting a well defined risk assessment and applying risk reduction techniques as prescribed by the Standard, appropriate measures can be applied to achieve the higher levels of safety and explosion prevention.
The heart of the matter
EN1127-1 1 page5/6 states:
“The preventive and protective measures described in EN 1127-1 will not provide the required level of safety unless the equipment, protective systems and components are operated within their intended use and are installed and maintained according to the relevant codes of practice or requirements. Since safety depends not only on equipment, protective systems and components but also on the material being handled and its use, this standard also includes aspects related to the intended use and foreseeable misuse, that is, the manufacturer should consider in which way and for which purpose the equipment, protective systems and components will be used and take this into account during their design and construction. This is the only way hazards inherent in equipment, protective systems and components can be reduced.”
This reiterates that safety is everyone’s responsibility and an ongoing process.
Protective systems and functional safety
The protection principle for the reduction of risk detailed within Clause 6 of EN 1127-1:2011 may be implemented via the use of protective systems. In some cases the protective system will make use of a measuring and control system (clause 6.7 of EN 1127), the general principles of which are covered under standard EN ISO 13849-1 (Safety of machinery – Safety-related parts of control systems, Part 1: General principles for design). This means that process control can be used for the basic principles of explosion prevention and protection as follows: -
* Avoidance of explosive atmosphere;
* Avoidance of effective ignition sources, see EN 13463-1 and -6;
* Reduction of explosion effects.
It is specified within Clause 6 of EN 1127-1:2011 that “Measuring and control systems used shall produce the appropriate response.” Additionally the required reliability of the monitoring and control system (see EN 50495 and EN 13463-6) follows from the risk assessment (see EN 15198 and EN 13463-1). Therefore the overall functional safety of the protective systems i.e. thermal or over-speed shutdown protection is vital for ensuring the correct and reliable operation of the equipment within a potentially explosive atmosphere.
In order to provide reliable shutdown of equipment in erroneous conditions, protective systems should be designed with the following functional safety in mind. Generally the functional safety design of protective systems needs to incorporate the following primary principles: -
* Intended use
* Possible operating faults (hazard and risk analysis)
* Safety Integrity Level (SIL)
* Reliability of protective systems (mechanical, electrical, electronic and software)
* Misuse which can reasonably be anticipated
For non-electrical equipment standard EN15198 ‘Methodology for the risk assessment of non-electrical equipment and components for intended use in potentially explosive atmospheres’ makes reference to standard EN 15233 ‘Methodology for functional safety assessment of protective systems for potentially explosive atmospheres’. This type ‘A’ standard describes principles for a consistent systematic procedure for functional safety assessment with respect to the design and manufacture of protective systems.
Is EN1127-1 applicable to my mechanical equipment?
(Source: Reference ATEX Guidelines 3.7.3)
If non-electrical equipment has a potential ignition source, (in most cases this is due to moving parts able to create a potential ignition risk either from hot surfaces, or frictional sparking) then EN1127-1 is applicable.
Examples are: gears, fans, pumps, compressors, mixers, brakes. Mechanical equipment of this type usually has to be connected to a power source, such as an electric motor. Together placed on the market in this form, it might be an assembly (an assembly, formed by combining two or more pieces of equipment, together with components if necessary, has to be considered as a product falling under the scope of Directive 94/9/EC).
Ignition sources to consider
~Flames and hot gases
~Mechanically generated sparks
~Stray electric currents, cathodic corrosion protection
~Radio frequency (RF) electromagnetic waves from 104 Hz to 3 x 1011 Hz
Electromagnetic waves from 3 x 1011 Hz to 3. x 1015 Hz
~Adiabatic compression and shock waves
~Exothermic reactions, including self-ignition of dusts
The introduction of the 2011 edition of the EN 1127 standard has introduced considerations regarding the tightness of equipment and has replaced clause 4 ‘Hazard identification’ with a risk assessment approach in accordance with EN ISO 12100 and/or EN 15198. The inclusion of these standards has introduced a functional safety consideration for protective systems that are relied upon to provide safety with regards to potential ignition sources under fault conditions on equipment. If an organisation is concerned about interpreting and applying Standards to their own equipment and environment, they should contact their partner validation and assessment company for guidance.
This paper is from the Intertek group, which provides testing, certification and related services across a wide range of industries worldwide.
Please visit www.intertek.com/hazardous-locations/ for more information.
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