Battery plants: why blood lead results do not replace air monitoring

A battery plant can have excellent blood lead results and a well-run medical surveillance program and still be in clear violation of OSHA's lead standard. The reason is that blood lead is not a record of what is in the air.

The mistake: letting blood lead testing replace air monitoring

OSHA's lead standard sets its own air monitoring requirement on its own schedule. After initial monitoring, how often you repeat it depends on the measured airborne lead concentration:

• At or above the action level: every 6 months
• Above the permissible exposure limit (PEL): every quarter
• You cannot leave the schedule until two consecutive results, at least 7 days apart, are below the action level

Blood lead results satisfy none of that. The initial monitoring must also establish exposure without regard to any respirator, which means the lead in the worker's breathing zone, not what got through the cartridge. Plants that switched to powered air-purifying respirators (PAPRs) and stopped air monitoring have a recordkeeping problem waiting for them.

The PEL is 50 micrograms per cubic meter of air (µg/m³), and the action level is 30 µg/m³. Records must be kept 40 years, or the length of employment plus 20 years.

→ How we monitor lead exposure

The blood lead triggers date from 1978

This is worth stating plainly, because it changes how you should read a good result.

The lead standard requires medical removal at a single blood lead of 60 micrograms per deciliter (µg/dL), or a three-test average of 50 µg/dL. Medical removal means taking the worker out of the lead job, and the worker may return below 40 µg/dL. Those numbers were set in 1978 and have never been revised.

Compare the values other organizations use:

• NIOSH defines an elevated blood lead level in adults at 5 µg/dL in its ABLES program.
• The reference value used alongside it, from the Council of State and Territorial Epidemiologists (CSTE), is now lower still at 3.5 µg/dL.
• ACGIH sets a guideline value for lead in blood of 30 µg/100 mL, the same as 30 µg/dL, which it calls a biological exposure index. It was adopted in 1995 and has not changed since.

A worker at 35 µg/dL is at 7 times the NIOSH elevated level, above the ACGIH biological exposure index and well inside the range OSHA accepts. All of those are true at once. Which one you manage to is your plant's decision, because the standard does not make it for you.

The other long-standing problem is lead going home with the worker. Change rooms, showers, separate lunchrooms and the ban on wearing work clothes home all exist because families of battery workers have been poisoned by lead on work clothes. That is what the housekeeping provisions of the lead standard are really for.

Formation and charging: two surveys in one room

Charging releases sulfuric acid mist as the cells gas. OSHA's PEL is 1 milligram per cubic meter of air (mg/m³). ACGIH's threshold limit value (TLV) is 0.2 mg/m³ on the thoracic fraction, the part of the mist fine enough to get past the throat, and ACGIH also places it in its A2 carcinogen category. The carcinogen classification applies to strong inorganic acid mists, not to liquid sulfuric acid, which is why the safety data sheet and the TLV seem to disagree.

Sampling acid mist properly takes a backup pad behind the mixed cellulose ester (MCE) filter, because not all of the mist stays on the filter. Some passes through, and the pad captures it.

The details differ by source. OSHA's current sampling instructions for sulfuric acid call for a backup pad impregnated with sodium carbonate, while the written analytical method (OSHA ID-113) describes a plain cellulose pad. That method is also only partially validated, not fully validated. Run the job with a bare filter cassette from the metals kit and you get a number that looks plausible, reads low and is useless.

The efficient approach is to sample for lead and acid mist on the same workers during the same shift. The sampling media differ, but it is one trip.

→ How we sample for acid mist

Cadmium, and a standard with its own medical surveillance

Plate making for nickel-cadmium (NiCd) batteries, pasting and recycling put you under OSHA's cadmium standard, which sets a PEL of 5 µg/m³ and an action level of 2.5 µg/m³. The standard has its own medical surveillance, built on cadmium in urine (in µg/g creatinine), beta-2-microglobulin and blood cadmium, not on a single number.

Cadmium damages the kidneys, so these tests look for early injury to the kidney tubules. They are not interchangeable with the lead program.

→ How we sample for cadmium

Lithium-ion: an entirely different chemical inventory

Electrode coating runs on the solvent 1-methyl-2-pyrrolidone (NMP), which has no OSHA PEL. ACGIH recommends 10 parts per million (ppm) with a skin notation, a flag that it can also be absorbed through the skin. NMP is also classified as a developmental toxicant, which makes it a question about your workforce as much as about the airborne concentration. The exposures occur at slurry mixing, at the coating head and during drying oven maintenance.

The hazard that gets missed is hydrogen fluoride. The electrolyte salt LiPF₆ breaks down into hydrogen fluoride (HF) on contact with moisture. Cell filling, formation, leak checks, teardown and any overheating event can release HF into the air, even in a plant whose chemical inventory has no acid. The OSHA PEL is 3 ppm, and the ACGIH TLV is 0.5 ppm as a time-weighted average (TWA) with a 2 ppm ceiling. Planning for an HF emergency is a different exercise from planning for a solvent emergency.

Handling cathode powder brings two more metals:

• Cobalt. The OSHA PEL is 0.1 mg/m³. ACGIH's TLV is 0.02 mg/m³ as inhalable dust, and ACGIH lists cobalt as a sensitizer, a substance the body can come to react to.
• Nickel compounds. OSHA has a single PEL of 1 mg/m³, which hides an ACGIH system that divides nickel into elemental, soluble and insoluble forms whose limits differ by more than ten times.

Recycling, and the reporting side

Battery breaking, desulfurization and smelting concentrate lead fume, and they can also add arsenic and antimony from the alloy metal. OSHA's arsenic standard sets a PEL of 10 µg/m³.

On the environmental side, lead falls under the Toxics Release Inventory (TRI), EPA's annual toxic chemical release reporting program. Lead is a persistent, bioaccumulative and toxic (PBT) chemical, so its reporting threshold is 100 pounds, with no de minimis exemption. The usual 25,000 and 10,000 pound thresholds do not apply, and no battery operation is under 100 pounds.

Form R is the full version of the TRI report. Arizona facilities that file one also owe the state a Toxic Data Report on the same July 1 deadline, and they must prepare a pollution prevention plan.

Lead-acid battery manufacturing also has its own federal air emission standard for smaller sources (EPA's Subpart PPPPPP), and secondary lead smelting is covered by Subpart X. Emission standard work is outside the four fields we work in.

→ How we handle Form R and TRI reporting · Arizona's pollution prevention plan and Toxic Data Report

What we do for battery plants

An air monitoring survey measures what your workers are breathing, and a noise survey measures the noise exposure of each job. For Form R, we make the threshold determination, run the calculations and file the report.