Sarath Bulathsinghala

18 Dec 2021

A bouquet of flowers to Dr Deshai Boteju for explaining the LPG fiasco in Sri Lanka so clearly for all to understand. What is most strange is that there is not a word from the Institution of Engineers, Sri Lanka on the issue!

Throughout Sri Lanka major issues with LPG usage in domestic environments cropped up almost overnight. The majority of these incidents came to notice during  November and December 2021 and continue to date.

Some of the causes of these explosions are blamed on the following.

• Change of gas composition from 30 % Propane / 70% Butane to 50% Propane / 50 % Butane
• A little or no smelling agent – Ethyl Mercaptan in the gas.  Ethyl Mercaptan is what makes propane gas smell. It’s an additive that is combined with liquefied petroleum gas, or LPG, to alert users of a leak.
• Gas cylinder attachments – the cylinder valve, the Pressure Regulator, the hose used outside warranty period.

Typical recent Gas explosion incidents in Sri Lanka

It is incumbent on the Suppliers – Litro Gas and Laugf to supply a safe product to the public, state clearly the constituents, include a Safety Data Sheet and operating instructions in the vernacular. This should be accompanied by safety instructions which include the type of attachments to be used and their specifications. These include the gas pressure regulator, the hose and the gas appliance such as cookers.

Safety instructions in a typical LPG set up in Australia

Faulty LPG gas cylinder valve: ideally this should have a pressure relief valve that can open to relieve excess pressure. This limit is normally set to 2585 kPa – 25.85 Barg (375 psig). The gas cylinder maximum bursting pressure limit is ~ 6895 kPa – 68.95 Barg(1000 psig). Typically, cylinders do not burst under normal domestic circumstances. Many are seen to be leaking from the valve, working well-outside their warranty period. The gas cylinder is a pressure vessel inside which the gas exists in two phases – as a liquid and as a gas at an equilibrium pressure which is equal to the Saturated Vapour Pressure (SVP) of the gas at that temperature. This pressure is only dependent on the outside temperature. As gas is released for use through the gas pressure regulator, more liquid will boil off to produce more gas till the bottle empties out. Till all the liquid is converted (evaporated) into gas the cylinder will remain at the SVP of the gas. Once all the gas in the liquid phase is over, the cylinder pressure will rapidly fall to atmospheric on use.

LPG cylinders are typically filled to 80%, meaning 80% liquid and 20% vapour

The primary function of an LPG gas regulator is to reduce the temperature dependent LPG gas bottle pressures varying from 400kPa – 4 Barg (58 psig) -1200kPa – 12 Barg (174 psig) down to the required 2.75kPa operating pressure for the gas appliances. Gas bottle pressure varies with temperature but the LPG gas regulator must be able to consistently maintain 2.75kPa (0.4 psig or 11 inches water column) . (Australian Specs).

All propane and LP Gas applications require the use of a regulator. Because pressures in propane tanks can fluctuate significantly, regulators must be present to deliver a steady flow pressure to downstream appliances. These regulators compensate for tank pressures in excess of 200 psig – 1378 kPa and commonly deliver 2.75 kPa (0.4 psig or 11 inches water column) for residential applications. Propane regulators differ in size, delivery pressure and adjustability but are uniform in their purpose to deliver a constant outlet pressure for downstream requirements.

This diagram shows conditions for propane gas pressure relevant to an ambient temperature of 1.7 deg C. This will change to 11.2 bar at 35 deg C. However, the outlet pressure should remain at 2.75 kPa or 11 inches water gauge for use in utensils such as cookers. This is the function of a properly functioning Pressure Regulator. Most countries that use 100% Propane see extreme temperature variations. These include – Australia and the US. 

Schematic diagram of a Pressure Regulator

The ambient temperature in Sri Lanka varies from a minimum around 15 deg C around Nuwaraeliya to a maximum of 35 deg C around Jaffna and Batticaloa. Therefore the gas regulators in Sri Lanka should withstand pressures of a maximum of 500 kPa (72.5 psig) corresponding to 35 deg C for 30% Propane to 70% Butane mixture and 650 kPa ( 94.3 psig) corresponding to  35 deg C  for 50%Propane and 50% Butane mixture.

The above-mentioned regulator for Australian Standards is well within this range. It is reasonable to believe that the gas regulators used in Sri Lanka even though may not be of good quality, but are manufactured to the same specifications. The upper bound 1200 kPa (174 psig) caters well for any pressure hikes well beyond the capacity of the gasses – even 100% Propane with a saturated vapour pressure of 1100 kPa – 11 Barg ( 159.5 psig) at 35 deg C.

On temperature variation alone – from 15 deg C to 35 deg C the maximum pressure variation is from 240 kPa for the 30/70  mixture and 340 kPa for the 50/50 mixture at 15 deg C to 500 kPa and 650 kPa respectively at 35 deg C. This shows that the pressure in the cylinder can rise from a minimum of 240 kPa to a maximum of 650 kPa on temperature variation alone, which is a 270 percent increase! However the gas regulator is supposed to absorb this variation and deliver only gas at 2.75 kPa (0.4 psig or 11 inches water column)  to the gas hose and through that to the appliance.

In summary, what can be said at this point in time is:

• Gas cylinder valves are old, leaky and working outside their warranty period.
• Increase in cylinder pressure due to change of gas composition  has led to cylinder valves leaking and pressure regulator malfunctioning, allowing higher outlet pressures at the user end – higher than 2.75 kPa.
• Utensils malfunctioning due to increased pressure leading to ‘poorly burnt gas’ and accumulation of leaked gas in poorly ventilated areas in a household – mostly the kitchen. Propane is 1.5 times and Butane 2.0 times heavier than air.
• Explosions of accumulated gas in the presence of a fire initiator such as opening or closing of an electrical switch, lighting a match stick or even the use of a mobile phone device making static discharges finally leading to an gas explosions.
• Timely servicing and maintenance of all attachments to a gas cylinder – the valve, the regulator, the pigtail hose and the appliance itself is of paramount importance.
• Signs of possible problems with a propane gas regulator or appliance include lazy yellow or orange flames; a popping noise when turning a gas burner off or on; flames floating above burner ports; roaring noises from burners; flames at the burner air intake; flames spilling out of the burner; and heavy deposits of soot …

(Most of the technical information above is from internet sources)

The quality of the gas supply from overseas should carry an internationally accepted product certificate issued by a certifying authority such as SGS or similar. From what is seen it is quite apparent that the Sri Lankan procurement services are ‘leaking like a sieves’open to abuse and corruption. All major imports including gas, coal, sugar, rice etc etc seems to lack transparency. New laws should be brought about to prevent such abuse.

Product certification – Whether the supply of gas is as per the Sri Lankan specification can easily be verified before shipment by an organisation such as the SGS. They supply a variety of services in the case of dispute resorting to an organization such as SGS for independent verification of products, services or practices. SGS certification is a certificate or report issued by SGS for compliance or testing services performed by SGS on a product or organization according to a country’s standards, regulations or customer requirements. SGS is the abbreviation of Societe Generale de Surveillance S.A., translated as “General Notary Public”. SGS is the world’s leading inspection, verification, testing and certification organization. It is a globally recognized benchmark for quality and integrity. SGS is an internationally recognized inspection, accreditation, testing and certification organization with more than 95,000 employees worldwide, located in more than 2,400 branches and laboratories, forming a global service network.