The battery charging process releases oxygen and hydrogen after a cell has achieved approximately 95% of its charge. The resultant risk is required to be assessed under Part 3.1 of the NSW Workplace Health and Safety Regulation 2011.
The NSW Work Health and Safety Regulation 2011 (WHS Reg) prescribes specific duties in relation to exposure standards for specific chemicals and mixtures and hazardous atmospheres at the workplace. Clause 51 to 52 of the regulation requires a person conducting a business or undertaking to manage risks to health and safety associated with a hazardous atmosphere at the workplace in accordance with Part 3.1, wherein:
An atmosphere is a hazardous atmosphere if:
- The atmosphere does not have a safe oxygen level, or
- The concentration of oxygen in the atmosphere increases the fire risk, or
- The concentration of flammable gas, vapour, mist or fumes exceeds 5% of the LEL for the gas, vapour, mist or fumes, or
- Combustible dust is present in a quantity and form that would result in a hazardous area
Airborne concentration of hydrogen gas can be measured using a range of direct reading instruments such as the Drager X-am 5000 with H2 sensor employed by Safe Environments, which can also pump air through Tygon tubing at heights with extendable carbon fibre poles. Hard installations can also be used and are recommended to provide continuous feedback on the airborne hydrogen gas concentration.
AS 3011.1 at Clause 2.1.5 Ventilation requires the hydrogen concentration by volume in a battery room or enclosure to be maintained below 2% and references AS 2676.1 Guide to the installation, maintenance, testing and replacement of secondary batteries in building Part 1: vented cells, to calculate airflow requirements. The airflow requirements are based on the number of battery cells, and the charging rate in amps.
It is best to stagger charging times to reduce the maximum airborne concentration. Battery charging rooms are at risk of the mechanical ventilation failing, which may lead to an increased build-up of hydrogen. Alarms must therefore be installed to provide a warning when the exhaust fan fails and high levels of hydrogen are encountered.
Potential hazards in battery charging rooms also include airborne sulphuric acid or potassium hydroxide, which can be avoided by wearing gloves and suitable eye protection when handling batteries. The risk is likely to be higher during summer months due to higher evaporation rates.
In addition to installing suitable hydrogen monitoring instruments, companies must also ensure employee awareness of the risks of hydrogen gas through training, Safe Work Method Statements (SWMS) and by promoting the use of PPE during battery charging.