Classification of Hazardous Areas

Schalk Kruger

Agenda

• Hazardous Area Classification Process• Flammability of Chemicals• Classification of Chemicals• Chemical Phase• Dispersion• Liquid Jet Breakup• Droplet Breakup Regimes• Dispersion Constraints• Dispersion Shapes• Solutions• Conclusion

Hazardous Area Classification

SOW, Team (SME is important), Chemicals, Operating Conditions, HAC Method (Direct Example, risk, SOR), HAC study, HAC drawings, approvals

Chemicals Flammability

Chemicals – Flammability (Methanol)

Information should be split between section 5 and section 9 of the MSDS as per Globally Harmonizing System (GHS) 5th Revised edition annexure 4

Chemicals – Flammability (Ethylene Glycol)

Information in correct section as per Globally Harmonizing System (GHS) 5th Revised edition annexure 4

Chemicals – ClassificationCAS No

Name &Formula

Rel. Dens

SG FP LFL UFL AIT MIE MESGMIC

RatioT Class

Equip.Group

67-56-1MethanolCH3OH

1.11 9oC 6% 36% 440oC 0.92 0.82 T2 IIA

107-21-1Ethylene Glycol C2H6O2

1.11 115°C 3% 7% 413°C 1.2mJ T2 IIA

• SANS 60079-10-1: flammable liquid – a liquid capable of producing a flammable

vapour under any foreseeable operating conditions

Ethylene Glycol flammability• Shell MSDS: No, product cannot ignite due to static electricity.• PHARMCO-AAPER MSDS: Flammable• NFPA 704: Classified as Code 1 i.e. materials that require considerable preheating before

ignition and combustion can occur.

Ethylene Glycol applications• Antifreeze i.e. freezing point depression• Safer alternative to formaldehyde i.e. biological specimen preservation• Treatment of dry rot in wood

P-T Phase Diagram

Dispersion - Liquid/Vapour

Dispersion type and distance

Flammability of Droplets

• Defined by the MIE

• Quenching distances i.e. distance between the droplets must allow flame propagation

• Droplets smaller than 50 µm creates a flammable atmosphere.

Liquid Jet Break-up

Change in jet break-up regime and length of solid liquid core with exit velocity

Liquid Jet Breakup

Breakup of a liquid jet, from Herrmann (2003)

Classification of droplet breakup regimes

Classification of droplet breakup regimes, from Reitz (1978), Lefebvre(1989), Faeth (1990) and Birouk and Lekic (2009).

Droplet breakup regimes

Secondary droplet breakup mechanisms, from Pilch & Erdman (1987).

Primary droplet breakup mechanisms, from Pilch & Erdman (1987).

Droplet breakup regimes

Secondary droplet breakup mechanisms, from Pilch & Erdman (1987).

Weber number

𝑊𝑒𝑔 =𝜌𝑔𝑈𝑑

2𝑑𝑑

𝜎• We = Weber number (Dimensionless)

• ρg = Gas density (typically the ambient air) (kg/m3)

• Ud = Relative velocity between droplet and air (m/s)

• dd = Characteristic length, typically the droplet diameter (m). Usually taken as Sauter Mean Diameter (SMD)

• σ = Surface tension of the droplet (N/m)

Weber number calculation to identify droplet breakup regime

Dispersion Constraints

• Congestion of SORs

• Obstacles to dispersion

• Enclosed spaces i.e. trapping of dispersion

Droplet breakup when striking a surface (any surface, liquid or solid)

Droplet Party

Dispersion Shapes

Gas/vapour with SpillageGas/vapour with Dripping

Gas/vapour

SANS 60079-10-1, Edition 2

Liquid

Video Clip of

Solutions

• IP15 - “Porous spray guards can be used around flanges and known potential leak points, causing the material to coalesce back to a liquid… rendering it non-hazardous.”

Conclusion

Legislative compliance promotes a safe and controlled environment.

“Hazardous Area Classification” is a statement that expresses an

action.

Hazardous Area Classification done properly provides multiple benefits.