the compliance of ammonia refrigeration plants with …

Safe Management of Ammonia Refrigeration Systems – May 2017 in Grantham

THE COMPLIANCE OF AMMONIA REFRIGERATION PLANTS WITH THE

DANGEROUS SUBSTANCES AND EXPLOSIVE ATMOSPHERES

REGULATIONS 2002 (DSEAR)

Maurice Young

Director – Food Storage & Distribution Federation

Principal Consultant & Director

Maurice Young Consulting

Safe Management of Ammonia Refrigeration Systems – May 2017 in Grantham Slide 2

Introduction…

➢ The ATEX 137 Workplace Directive (1999/92/EC) has been implemented in the UK as the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).

➢ Similar regulations will apply in other EU Member States

➢ These regulations require Hazardous Area Classification (HAC) to be carried out where there may be a risk of explosion due to the presence of flammable substances in the form of gases, vapours, mist or dust.

➢ The regulations also require that to ensure safe operation, any equipment (both electrical and non-electrical) used in a classified area falls within the scope of the regulations and must therefore be suitable for use in the respective zone.

➢ DSEAR is concerned with normal operations and does not extend to catastrophic failures or similar emergency conditions that are covered by other H&S regulations.


When did DSEAR come into force…

Workplace Date when DSEAR/ATEXrequirements must be met

Workplace in use before July 2003(Equipment already in use before July 2003 can continue to be used indefinitely provided a risk assessment shows it is safe to do so).

Workplace must meet requirements by July 2006.

Today all ammonia refrigeration systems within the UK are required to comply with DSEAR.

Workplace in use before July 2003 but modified before July 2006.

Workplace must meet requirements from the time the modification takes place.

Workplace comes into use for the first time after June 2003.

Workplace must meet requirements from the time it comes into use.


The requirements under DSEAR…


The requirements under DSEAR…

Regulations/the Law MUST be obeyed

ACoPS have a special legal status. If you follow the guidance you SHALL normally be doing enough to comply with the law

Standards SHOULD normally provide details of approved good practice but REMEMBER – the LAW TRUMPS a STANDARD


The UK enforcement strategy…

➢ The Health and Safety Executive (HSE) has stated that it is a legal requirement of DSEAR that machinery rooms and other plant areas containing potential sources of release of group #2 (Ammonia is B2 group refrigerant) and #3 refrigerants shall comply with the requirements of hazardous area classification.

➢ Further, the HSE has clarified that the requirement for area classification applies to any parts of the plant that include sources of release and is not restricted solely to machinery rooms.

➢ It is the possibility of a release of a flammable substance that triggers the need for area classification to be carried out: Under CLP Regulations ammonia is classified as flammable

(Hazard Statement H221) There are other flammable refrigerants – for example R32

and R1234yf (both H220) are classified as ‘extremely flammable’.


Area classification strategy…

➢ Area classification is normally carried out by reference to established codes, using more quantitative methods that require knowledge of the plant.

➢ The starting point is to identify sources of release of flammable gas or vapour.

➢ DSEAR is concerned with releases that rise from constant activities; from time to time in normal operation.

➢ Catastrophic failures, such as vessel or line rupture are not considered by an area classification study. A hazard identification process such as a Preliminary Hazard Analysis (PHA) or a Hazard and Operability Study (HAZOP) should consider these abnormal events.

➢ The most commonly used standard in the UK for determining area classification is BS EN 60079 part 10-1.


BS EN 60079-10-1:2009…

➢ BS EN 60079-10-1:2009 classified hazardous areas on the basis of the size of an anticipated hazardous volume of gas (Vz).

Vz is a hypothetical gas cloud volume

Mean concentration of 25% LEL (for primary releases) and 50% LEL (for secondary releases) equal to a safety factor of 2 & 4.

Determines level of ventilation (high, medium or low)

If Vz is less than 0.100m3, ventilation is regarded as high and the zone is classified to be of Negligible Extent (NE) and normally no precautions against ignition are required.

➢ However, the empirical equation for the calculation of Vz

included in BS EN 60079-10-1:2009 has no scientific basis and results in overly conservative results.


BS EN 60079-10-1:2015…

➢ The 2015 Edition replaces Vz with a new methodology that allows a zone dimension to be determined from the release characteristic and consideration of the type of release using diagrams.

➢ However, easily missed in the national foreword on page 2 is a disavowal by the British technical committee of the new methods presented.

➢ With the UK committee statement, three possible approaches suggest themselves:

Fall back onto EI Model code of safe practice Part 15: Area classification for installations handling flammable fluids;

Fully CFD model the potential releases;

Refer back to the 2009 revision and approach using Vz, together with the intervening HSL research.


New methodology for calculating Vz based upon HSL research…

A calculated Vz of 0.100m3 or <1% of the enclosure volume using this method allows in normal circumstances zones of negligible extent to be assigned.


Vz – graph showing the relationship between room volume and the available ventilation …


Limitations of the methodology…

1) The value of Vz depends on the cube of the radius of the hole and is therefore sensitive to it. Care is required not to underestimate (or overestimate) hole size.

2) The build-up of flammable gas can be strongly affected by local obstructions to the resulting jet and to the ventilation flow.

3) A preliminary assessment of the effects of confinement on the gas cloud build-up can be carried out by assigning an appropriate value to the efficiency of mixing. Typically either Є = 0.3, 0.5, rather than 1 should be used.

5) Ventilation must permeate the whole room.

6) Above 20barg zones of NE should not be automatically assigned without further assessment.


Grades of release…

➢ There are three defined grades of release; continuous, primary and secondary. Generally, these three defined grades give rise to hazardous areas classified as Zones 0, 1, and 2 respectively.

➢ Zone 0 - a place in which an explosive gas atmosphere is present continuously or for long periods or frequently.

➢ Zone 1 – a place in which an explosive atmosphere is likely to occur in normal operation occasionally, (Examples include sampling points, pressure relief valves, drainage points).

➢ Zone 2 – a place in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short duration of time only. (Examples include near flanges, pipe fittings, valve stems, pump glands, full bore emissions from pressure relief valves).


Simplified refrigeration circuit…


Hole size selection…


Ammonia gas release – 2.50mm2 hole at 13barg…


Ammonia liquid release – 0.25mm2

hole at 13barg…


Typical Hazardous Area Classification Examples & Documentation…

Anhydrous Ammonia as a refrigerant (R717)

Plant Item LocationGrade of

Release

Hole Size

(mm2)oC Barg Type Degree

Note A Note B Note C See tab Note E Note F Note G Note H Note I Note J Note K Note L

Ventilation Grade of

Release

(Zone)

Operating

Temperature &

PressureLeak

Reference

Notes

(See also comments that might appear

when curser is rolled over cell)

Hazardous

Cloud - Vz

(m3)

Distance to LEL

(m)

Release

Note D

Hazard Range

(m)

Background

Concentration

(%)

Plant Details: Drawing References: Flammable Material:

Ammonia Machinery Room - MR_01

MACHINERY ROOM

Review of current 'worst' case scenarios during normal operating conditions

Secondary 2.50 ≥ 35 13 Mech 4ACH Zone 2 ERV ER 0.410 58%

EN378 states that minimum ventilation

rate when room is occupied must be not

less than 4 air changes per hour.

Secondary 2.50 ≥ 35 13 Mech 8ACH Zone 2NE 0.035 0.929 0.246 30%

Ventilation required during normal

operating conditions to ensure Vz is

approximately ≤ 0.060m3 (Rounded up)

1.2 HP liquid line (various) Machinery room Secondary 0.38 ≥ 37 13 Mech 8ACH Zone 2NE 0.037 0.881 0.307 19% Vz similar to worst case gas line

10ACH Zone 2NE 0.071 1.060 0.334 26%Check for possiblity of congested leak

(30% mixing efficiency)

Review of current 'worst' case scenarios when refrigeration equipment is idle during COLD WEATHER CONDITIONS - less than 0oC.

1.3 Compressor seal Machinery room Secondary 1.00 ≥ -9 3 Mech 2ACH Zone 2NE ≤ 0.001 0.179 0.070 13%

When plant is idle for long periods of

time during low ambient temperatures

ventilation can be reduced to 2 air

changes per hour equivalent to a flow

1.4 HP liquid line Machinery room Secondary 0.25 ≥ -1 3 Mech 2ACH Zone 2NE 0.010 0.464 0.178 16%

Review of current 'worst' case scenarios when refrigeration equipment is idle during AVERAGE WEATHER CONDITIONS - approximately 11oC.

1.5 Compressor seal Machinery room Secondary 2.50 ≥ 10 6 Mech 6ACH Zone 2NE 0.034 0.923 0.228 32%

When plant is idle for long periods of

time during average ambient

temperatures ventilation can be

reduced to 6 air changes per hour

1.6 HP liquid line Machinery room Secondary 0.38 ≥ 15 6 Mech 6ACH Zone 2NE 0.018 0.628 0.288 14%

1.1 Compressor seal Machinery room





Release

Hole Size




Release

(Zone)

Operating

Temperature &

PressureLeak

Reference

Notes



Hazardous

Cloud - Vz

(m3)

Distance to LEL

(m)

Release

Note D

Hazard Range

(m)

Background

Concentration

(%)



2.1 Compressor seal Compressor (shaft seal) Secondary 2.50 ≥ 35 13 Mech 10ACH Zone 2NE 0.023 0.723 0.228 24%

2.2 HP gas line Compressor Secondary 0.38 ≥ 35 13 Mech 10ACH Zone 2NE ≤ 0.001 0.160 0.071 4%

2.3 IP gas line Compressor Secondary 0.38 ≥ 25 10 Mech 10ACH Zone 2NE ≤ 0.001 0.142 0.063 3%

2.4 LP gas line Compressor Secondary 0.38 ≥ -19 2 Mech 10ACH Zone 2NE ≤ 0.001 0.079 0.036 1%

2.5 HP liquid line Compressor Secondary 0.38 ≥ 37 13 Mech 10ACH Zone 2NE 0.029 0.793 0.296 16% See also 1.2 for worst case check

3.1 LP gas line Surge drum Secondary 0.38 ≥ -19 2 Mech 10ACH Zone 2NE ≤ 0.001 0.079 0.036 1%

3.2 HP liquid line Surge drum Secondary 0.38 ≥ 37 13 Mech 10ACH Zone 2NE 0.029 0.793 0.296 16%

3.3 IP liquid line Surge drum Secondary 0.38 ≥ 15 6 Mech 10ACH Zone 2NE 0.012 ,563 0.256 9%

3.4 LP liquid Line Surge drum Secondary 0.38 ≥ -8 2 Mech 10ACH Zone 2NE 0.006 0.437 0.225 4%

4.1 HP gas line Intercooler Secondary 0.38 ≥ 35 13 Mech 10ACH Zone 2NE ≤ 0.001 0.160 0.071 4%

4.2 IP gas line Intercooler Secondary 0.38 ≥ 25 10 Mech 10ACH Zone 2NE ≤ 0.001 0.142 0.063 3%

4.3 HP liquid line Intercooler Secondary 0.38 ≥ 37 13 Mech 10ACH Zone 2NE 0.029 0.793 0.296 16%

4.4 IP liquid line Intercooler Secondary 0.38 ≥ 15 6 Mech 10ACH Zone 2NE 0.012 ,563 0.256 9%

4.5 LP liquid Line Intercooler Secondary 0.38 ≥ -8 2 Mech 10ACH Zone 2NE 0.006 0.437 0.225 4%

5.1 HP gas line HP Receiver Secondary 0.38 ≥ 35 13 Ambient N/A Zone 2NE ≤ 0.001 0.148 0.068 N/A HP receiver is located outdoors

5.2 HP liquid line HP Receiver Secondary 0.38 ≥ 37 13 Ambient N/A Zone 2NE 0.012 0.546 0.294 N/A

6.1 HP gas line Condenser Secondary 0.38 ≥ 35 13 Ambient N/A Zone 2NE ≤ 0.001 0.148 0.068 N/A Condenser is located outdoors

6.2 HP liquid line Condenser Secondary 0.38 ≥ 37 13 Ambient N/A Zone 2NE 0.012 0.546 0.294 N/A

7.2 LP liquid lineDrain on evaporator inside

freezerSecondary 0.25 ≥ -8 2 Natural 2ACH Zone 2NE 0.026 0.758 0.231 30.000

Results of worst case exercises above indicate that ventilation rate during normal operating conditions should be around 10 air changes per hour to allow for the possibility of congested air flows existing around potential ammonia leaks.

AREA CLASSIFICATION OF TYPICAL LEAKS IDENTIFIED THROUGHOUT THE SYSTEM





Release

Hole Size




Release

(Zone)

Operating

Temperature &

PressureLeak

Reference

Notes



Hazardous

Cloud - Vz

(m3)

Distance to LEL

(m)

Release

Note D

Hazard Range

(m)

Background

Concentration

(%)



Protective devices

Fugitive release during

normal operationPrimary 0.25 ≥ 35 13 Ambient N/A Zone 1 ≤ 0.001 0.120 0.055 N/A

PRV have been regularly re-calibrated

and/or replaced

Upon lifting Secondary 250.00 PRV 21 Ambient N/A Zone 2 5.032 4.651 2.137 N/A Ensure 3m ignition free zone

8.1Pressure relief valves

(PRVs)


EN378-3:2016 - Ventilation…

➢ 5.13.1 The ventilation of machinery rooms shall be sufficient both for normal operating conditions and emergencies.

➢ 5.13.2 Ventilation shall be in accordance with national regulations with a minimum of 4 air changes per hour when the machinery room is occupied. The Management of Health and Safety at Work Regulations

PUWER

➢ In the event that the necessary ventilation rate cannot be achieved an audible and/or visual alarm shall be initiated and, where relevant, electrical supplies shall be terminated.

➢ In 99% of cases when machine rooms are adequately sized to enable maintenance and well ventilated DSEAR compliance is straightforward – but you must do the assessment and area classification.


Conclusions…

➢ For new ammonia refrigeration systems making sure that the requirements of DSEAR are integrated at an early stage into the design phase of a project should lead to better systems that are cost-effective (possibly ‘no-cost’) and fully compliant.

➢ For existing ammonia refrigeration systems there may be some greater obstacles to overcome particularly where machinery rooms are extremely small and/or poorly ventilated.

➢ The law requires that both risk assessments and area classifications are undertaken for ammonia systems.

➢ EN378 and ISO5149 (and other standards such as ASHRAE15) DO NOT address DSEAR and they ignore other spaces where refrigeration equipment is installed.

➢ The relevant laws must be complied with but the standards should also be considered.

Safe Management of Ammonia Refrigeration Systems – May 2017 in Grantham

THANK YOU FOR YOUR ATTENTION

ANY QUESTIONS…?

The subject covered in this presentation has also been reported in the following technical papers:

6th IIR Ammonia Technology Conference in Ohrid, Macedonia in April 2015 (M. J. Young)

24th IIR International Congress of RefrigerationYokohama, Japan in August 2015 (A. B. Pearson & M. J. Young)

Presentation to IoR, South Bank University, London in October 2015 (M. J. Young & A. B. Pearson)

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