R&R wish to market a series of aerosol microleak detectors in the UK which will form a key element of the UN approved alternative test method for aerosol testing to ensure aerosols leaving an aerosol filling operation are safe for transport and safe to the consumer.
Halliday, Stack & Dewhirst Ltd. (HSD) Ltd were approached by R&R to verify that their machines comply with the regulations governing the transport of dangerous goods by road, rail, sea and air (ref 1) as implemented in the UK by the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations 2009 (CDG 2009).
The machines which R&R wish to market are manufactured in the UK by R&R themselves and utilize a vacuum decay principle.
- The European Agreement Concerning the International Carriage of Dangerous Goods by Road (ADR), Regulations Concerning the International Carriage of Dangerous Goods by Rail (RID), The International Maritime Dangerous Goods Code (IMDG) & The Technical Instructions for the Safe Transport of Dangerous Goods by Air (ICAO TIs)
Aerosol dispensers (aerosols) have been in commercial production for around fifty years. Aerosols use pressure from liquefied, or permanent gas (propellant) to provide the driving force to dispense the product from the aerosol can. The internal pressure from the propellant means that aerosol cans store a significant amount of energy which, if suddenly released (i.e. a bursting can), would have the potential to give rise to high velocity missiles (can fragments). In addition the active ingredients are often flammable and the liquefied gas propellants commonly used are highly flammable (e.g. propane / butane mixtures, or dimethyl ether (DME) and if these are released either due to a leak from a can, or due to a can bursting, they may pose fire and explosion hazards. In manufacture of aerosol products it is therefore necessary to confirm that the containers are acceptably leak tight and pressure stable, so that when they are stored, transported and sold to the public there is minimal risk of them causing injuries or property damage through bursting or leaking (i.e. resulting in a fire / explosion). In regulatory terms this means complying with EU and international transport regulations for dangerous goods and the Aerosol Dispensers Directive (75/324/EEC).
In the 1990s, the European Aerosol Federation (FEA) investigated possible ‘alternative methods’ to the hot water bath and concluded that for an ‘alternative method’ to be acceptable it must be shown to be as effective as the hot water bath test at eliminating faulty and leaking aerosols. In 2002, to demonstrate this principle FEA developed the ‘FEA alternative method’, based on the principle that quality assurance and on-line testing may be used to ensure that all sub-standard aerosols are eliminated before they leave the filling line.
The UN Sub-Committee of Experts on the Transport of Dangerous Goods which accepted the findings of the FEA trial and incorporated an option for ‘alternative methods’ into the UN 2005 Model Regulations for the Transport of Dangerous Goods. The option permits, with the approval of the Competent Authority, the use of alternative methods to the Water Bath test which provide an equivalent level of safety to ensure that filled aerosols are safe to be transported as ‘dangerous goods’ and is now implemented in the UK by the Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations 2009 (CDG).
The Dangerous Goods Division of the Department for Transport (DfT) performs the functions of the UK Competent Authority for the CDG regulations.
Normally, when the FEA guidance is followed it will only be necessary to ascertain that the company’s implementation of it incorporates all of the essential features and that it is operating effectively.
FEA Alternative Method
The ‘FEA Alternative Method’ is an integrated Quality Assurance and testing package which aims to ensure substandard aerosols are identified and rejected before they enter transport and distribution. It is currently the only method which has been demonstrated to comply with the requirements of ADR. Briefly the ‘FEA Alternative Method’ comprises the following key elements:
- Pressure testing of all empty aerosols by the can manufacturer to ensure that they do not deform when filled and leak at a rate less than 3.3 x 10-2 mbar.l.s-1.
- Quality Assurance procedures by the valve supplier to ensure that only valves that have all their components in place and that will be pressure stable and leak tight once crimped on a can are supplied to the filler.
- Quality Assurance procedures are used during handling and filling to check that only high quality aerosols are produced. Procedures include:
- Checks on the crimping equipment settings to maintain the correct valve crimp dimensions.
- In-line check-weighing to ensure overfilled aerosols are rejected.
- Leak testing of all filled aerosols to show that they do not leak at a rate ≥ 2.0 x 10-3 mbar.l.s-1 at 20°C
The VCA and BAMA both recommend that companies wishing to use an ‘alternative method’ to the Hot Water Bath test follow this system developed by FEA. Because it has already been proven to comply with the requirements of ADR the verification exercise would therefore be limited to demonstrating that the company has implemented and is adhering to a system that complies with the ‘FEA Alternative Method’.
- DESCRIPTION OF DETECTOR
R&R have developed two styles of microleak detection systems for the detection of micro leaks from aerosols. The two systems operate using the same vacuum decay principle but focus on different parts of the filled aerosol can.
The smallest microleak detection ‘head’ is presented to the top of a filled aerosol only, and will only detect leaks from the valve crimp or a faulty valve. As the cans have been pre-tested at the can manufacturer’s facility, leaks from the seam, shoulder or toe crimps will have been removed leaving the final crimp and valve as the only possible leakage points post filling. Clearly this is suitable for tin-plate cans as described in the approved alternative method.
The second larger leak detection head is designed to look for leaks from any part of the filled aerosol and fully encloses the whole can during test. The main benefit of whole can testing is leak detection on crimped seams and the side weld or stress fractures.
Each type of leak detection head has a dedicated controller which in turn communicates with the main machine PLC to accept or reject the can under test.
A dedicated reject unit will be fitted to the machine to reject cans that leak.
Both R&R microleak detection heads use a vacuum decay system for leak detection, which is described as a suitable method of leakproofness testing in the VCA’s Dangerous Goods Guidance note No. 002. The use of a vacuum decay system means that it will work for any propellant gas type, be it LPG, compressed air, nitrogen or CO2.
- TEST METHOD
Leaking aerosols were simulated by fitting an adjustable flow control device to a special the ‘threaded’ valve cup of an aerosol, which could be adjusted to hold open the valve to give the desired leak rate.
The leakage rate was established by adjusting the screw and observing the growth of a soap bubble against a caliper gauge set to 2.5mm. Once established the leakage rate was verified by HSD.
Next, the test aerosol was inserted into the test head and then observed to see whether the leak was detected.
The test aerosol was then rechecked in the same way as before to verify that it was still leaking at the required rate.
The test was repeated for a number of leaking and non-leaking cans and for both heads to verify that the systems would reliably detect the test aerosol.
This test protocol is broadly in-line with that proposed by BAMA in their draft guidelines to validating of leak detection systems for water-bathed aerosol dispensers.
1 HSD conclude that the systems as supplied by R&R are capable of fulfilling the requirements for the leak tester requirements of filled aerosols as part of the FEA ‘Alternative Method’ in compliance with the CDG regulations.
2 Installation of one of the R&R systems does not of itself guarantee full compliance with the FEA Alternative Method, only that part relating to aerosol leak detection.
3 HSD conclude that the R&R systems comply with the water-bath alternative test requirements of the BAMA standard however compliance of the entire filling operation with that standard is dependent on further measures and therefore not guaranteed by its installation alone.
P.R. Dewhirst C.Eng. M.I.Chem.E.
Loss Prevention Consultant Halliday, Stack & Dewhirst Ltd.